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A behavioral and anatomical examination of the intramodal and intramodal effects of early stimulation… Buhrmann, Kristin 1990

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A BEHAVIORAL AND ANATOMICAL EXAMINATION OF THE INTRAMODAL AND INTERMODAL EFFECTS OF EARLY STIMULATION HISTORY AND SELECTIVE POSTERIOR CORTICAL LESIONS IN THE RAT By K r i s t i n Buhrmann B . S c , The U n i v e r s i t y o f L e t h b r i d g e , 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA August 1990 (c) K r i s t i n Buhrmann, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of PL.06) Y The University of British Columbia Vancouver, Canada Date 2-i2. • 0&-SO  DE-6 (2/88) i i A B S T R A C T A BEHAVIORAL AND ANATOMICAL EXAMINATION OF THE INTRAMODAL AND INTERMODAL EFFECTS OF EARLY STIMULATION HISTORY AND SELECTIVE POSTERIOR CORTICAL LESIONS IN THE RAT by K r i s t i n Buhrmann The aim of t h i s study was to investigate the i n t r a - and intermodal impact of d i f f e r e n t kinds of early sensory experience on the development of s p e c i f i c neural/perceptual systems. The manipulations of the r a t s ' early experience involved a combination of early binocular deprivation through dark-rearing, somatosensory r e s t r i c t i o n through cauterization of mystacial v i b r i s s a e , and multimodal enrichment through rearing i n a complex environment. S p e c i f i c lesions to somatosensory (Pari) and v i s u a l (Oc2M) cortex i n d i f f e r e n t i a l l y reared animals were included i n an attempt to gain further insight into the p l a s t i c i t y surrounding manipulations of early stimulation h i s t o r y . Five tasks were used to assess these e f f e c t s of early rearing condition i n combination with l a t e r c o r t i c a l lesions. Behavioral assessment focused on the a b i l i t y of the animals to encode, abstract, and remember s p e c i f i c r e l a t i o n s h i p s between i i i s t i m u l i within the deprived modality i t s e l f , t h e i r a b i l i t y to do so with information presented i n other modalities, and on the basic species s p e c i f i c behavior. The only e f f e c t found was a main e f f e c t for rearing condition. B a s i c a l l y , complex-reared rats were more competent on several of the behavioral tasks than were dark-reared r a t s . However, t h i s r e s u l t provided l i t t l e behavioral support f o r ideas of modality interdependence. Dendritic p r o l i f e r a t i o n i s considered to be a general mechanism supporting behavioral change. The subsequent neuroanatomical assessment focused on d e n d r i t i c branching of neurons i n s p e c i f i c c o r t i c a l areas thought to be most affected by early environmental manipulations. Animals that were raised i n a complex environment, but had experienced early t a c t i l e r e s t r i c t i o n through cauterization of v i b r i s s a e , showed s i g n i f i c a n t l y more de n d r i t i c branching than animals from a l l other rearing conditions i n a l l c o r t i c a l areas measured. This f i n d i n g i s consistent with ideas of both i n t r a - and intermodal compensation following damage to an early developing modality, as well as behavioral demand acting as a s i g n i f i c a n t factor i n determining the impact of early somatosensory r e s t r i c t i o n . I t i s reasonable to assume that anatomical changes should be manifested behaviorally. Suggestions f o r smaller, more r e s t r i c t e d studies, that would be more e f f e c t i v e i n describing the behavioral impact of early manipulations of the environment, were outlined. i v TABLE OF CONTENTS Abstract i i L i s t of Tables v L i s t of Figures v i Introduction 1 Methods 23 Subjects 23 Environments and Rearing Conditions 23 Surgery 24 Behavioral Tasks 26 Grooming Behavior 28 Dodging and Wrenching 28 V i s u a l / T a c t i l e Novelty Discrimination 29 Water-based Spatial Learning Task 31 Water-based Concurrent Visual Discrimination Task...33 Histology and Anatomy 36 Results 40 Behavioral Tasks ...40 Grooming Behavior 40 Dodging and Wrenching 41 V i s u a l / T a c t i l e Novelty Discrimination 44 Water-based Spatial Learning Task 46 Water-based Concurrent V i s u a l Discrimination Task...49 Histology and Anatomy 53 V e r i f i c a t i o n of Lesion Location 53 Dendritic Arborization 58 Apical Dendrites 59 Ba s i l a r Dendrites 66 Discussion 67 Impact of Early Stimulation History on Behavior 67 Selective Posterior C o r t i c a l Lesions 75 Dendritic Arborization 78 Conclusions 81 References 83 V LIST OF TABLES Table 1. D e s c r i p t i o n of the b e h a v i o r a l impact of unimodal and multimodal environmental m a n i p u l a t i o n s 15 Table 2. D e s c r i p t i o n of the t r i a l s i n the Water-Based S p a t i a l L e a r n i n g Task 32 Table 3. D e s c r i p t i o n of the t r i a l s on Day 11 of the Water-Based Concurrent D i s c r i m i n a t i o n Task 35 v i LIST OF FIGURES F i g u r e 1. The r e p r e s e n t a t i o n of v i b r i s s a e r e c e p t o r s by t h e i r c o r r e s p o n d i n g b a r r e l formations i n the c o n t r a l a t e r a l primary somatosensory c o r t e x (Par 1) of the r a t 6 F i g u r e 2. The o n t o g e n e t i c sequence of emergence of sensory systems. (From G o t t l i e b , 1971) 8 F i g u r e 3. Connections of primary and secondary sensory r e g i o n s t o the p o s t e r i o r p a r i e t a l c o r t e x i n the r a t . (From Kolb, 1990) 17 F i g u r e 4. Design of the experimental groups i n c l u d e d i n the study 27 F i g u r e 5. A) Example of l a y e r V Pyramidal c e l l s drawn from somatosensory (Area P a r i ) , v i s u a l (Area Oc2M), and a u d i t o r y c o r t e x (Area T e l ) . B) I l l u s t r a t i o n of the c e n t r i f u g a l o r d e r i n g system; the r o o t segment i s the o r d e r 0 segment 38 F i g u r e 6. A) T o t a l d u r a t i o n of grooming i n seconds over the f i v e minute grooming t a s k f o r r a t s i n a l l f o u r r e a r i n g c o n d i t i o n s . B) T o t a l number of grooming components (body p a r t s ) groomed over the t o t a l d u r a t i o n of grooming 43 F i g u r e 7. R a t i o of t o t a l time spent e x p l o r i n g the n o v e l o b j e c t over t o t a l time spent e x p l o r i n g the f a m i l i a r o b j e c t d i s p l a y e d by r a t s i n the t h r e e s u r g i c a l c o n d i t i o n s on the T a c t i l e N o v e l t y D i s c r i m i n a t i o n Task 45 F i g u r e 8. A) Latency i n seconds t o f i n d the submerged p l a t f o r m a c r o s s T r i a l s 4, 8, 12, and 16 f o r animals i n a l l r e a r i n g c o n d i t i o n s . B) Latency and s t a n d a r d d e v i a t i o n t o f i n d the p l a t f o r m on T r i a l 4 f o r a l l r a t s i n a l l f o u r r e a r i n g c o n d i t i o n s 48 F i g u r e 9. Mean l a t e n c y i n seconds t o f i n d the cued submerged p l a t f o r m on T r a i n i n g Days 1, 5, and 10 f o r r a t s i n a l l f o u r r e a r i n g c o n d i t i o n s 50 F i g u r e 10. Mean number of t o t a l e r r o r s committed i n f i n d i n g the submerged p l a t f o r m on T r a i n i n g Days 1, 5, and 10 f o r r a t s i n a l l r e a r i n g c o n d i t i o n s 52 F i g u r e 11. Mean escape l a t e n c y i n seconds t o f i n d the cued p l a t f o r m on T r a n s f e r T r i a l s 5 and 6, f o r r a t s i n a l l r e a r i n g c o n d i t i o n s . These t r i a l s r e p r e s e n t the s i t u a t i o n where the o r i g i n a l cue p a i r s from the t r a i n i n g p o r t i o n of the c o n c u r r e n t d i s c r i m i n a t i o n t a s k are mixed 54 v i i Figure 12. Reconstruction of A) P a r i , primary somatosensory cortex containing the v i b r i s s a e barrel f i e l d s , and B) 0c2M, e x t r a s t r i a t e v i s u a l cortex lesions 56 Figure 13. A) Mean of mean number of de n d r i t i c branches for rats i n a l l rearing conditions i n area P a r i . B) Mean of mean number of higher order branching f o r rats i n a l l rearing conditions i n area Pari 61 Figure 14. A) Mean of mean number of de n d r i t i c branches found i n secondary v i s u a l cortex, area 0c2M for rats i n a l l rearing conditions. B) Summary of mean of mean number of higher order d e n d r i t i c branches for rats i n a l l four rearing conditions i n area 0c2M 63 Figure 15. A) Mean of mean number of den d r i t i c branching found i n primary auditory cortex, area T e l , a sensory system not d i r e c t l y manipulated, for rats i n a l l four rearing conditions. B) Summary of mean of mean number of higher order d e n d r i t i c branches f o r rats i n a l l four rearing conditions i n area Tel 65 1 I n t r o d u c t i o n For i n v e s t i g a t o r s i n t e r e s t e d i n the g e n e r a l p r i n c i p l e s u n d e r l y i n g b e h a v i o r a l p l a s t i c i t y , the e f f e c t s of e a r l y s t i m u l a t i o n h i s t o r y on the development of sensory and p e r c e p t u a l competencies have been an important and a c t i v e area of study ( A s l i n , 1981; Greenough, 1976; Tees 1976, 1986). The r o l e t h a t environmental i n p u t p l a y s i n determining the course of p e r c e p t u a l development i s m u l t i f a c e t e d . G o t t l i e b (1976, 1983) d e f i n e s t h r e e primary ways i n which e x p e r i e n t i a l and g e n e t i c f a c t o r s c o u l d t h e o r e t i c a l l y i n t e r a c t i n the development of p e r c e p t u a l a b i l i t i e s . Maintenance d e s c r i b e s the s i t u a t i o n where a p a r t i c u l a r p e r c e p t u a l a b i l i t y i s a l r e a d y f u l l y e s t a b l i s h e d , however, the subsequent appearance a s p e c i f i c environmental f a c t o r i s necessary t o m a i n t a i n the a b i l i t y . Should the organism not have the ex p e r i e n c e , the p e r c e p t u a l a b i l i t y d e c l i n e s . In f a c i l i t a t i o n the development of a p e r c e p t u a l a b i l i t y i s a c c e l e r a t e d or augmented by the a v a i l a b i l i t y of s p e c i f i c e x p e r i e n c e s . The r o l e of experience i s a l s o important i n the case of i n d u c t i o n . Here, the nature of a p e r c e p t u a l a b i l i t y would be a l t e r e d depending on s p e c i f i c e x periences a v a i l a b l e t o the organism. Other i n v e s t i g a t o r s ( A s l i n , 1981; Tees, 1990) have c o n t r i b u t e d t o f u r t h e r e l a b o r a t i o n s of the G o t t l i e b i a n framework d e s c r i b i n g the i n t e r a c t i o n between experie n c e and g e n e t i c s . A s l i n (1981) emphasizes t h a t the nature of e x p e r i e n c e t h a t i s i n f l u e n t i a l i s d i f f e r e n t a t d i f f e r e n t stages of development. 2 In any case, the use of t h r e e somewhat d i s t i n c t m a n i p u l a t i o n s of e a r l y experience - d e p r i v a t i o n , b i a s e d r e a r i n g , and enrichment - have emerged as techniques t o h e l p expose some of the i n t e r a c t i o n s between g e n e t i c and e x p e r i e n t i a l f a c t o r s . D i f f e r e n c e s , o r l a c k of d i f f e r e n c e s , found when comparing the beha v i o r of animals r e a r e d under d i f f e r e n t c o n d i t i o n s have e s t a b l i s h e d the r e l a t i v e c o n t r i b u t i o n s normally made by e x p e r i e n t i a l f a c t o r s t o s p e c i f i c d i s c r i m i n a t i v e b e h a v i o r s . With r e s p e c t t o competencies t h a t c o u l d be measured s h o r t l y a f t e r b i r t h , such techniques c o u l d be e a s i l y adapted t o examine whether sensory experience p l a y e d a r o l e i n t h e i r subsequent development. In many cases i n v o l v i n g the impact o f c o n t r o l l e d r e a r i n g , t h e r e appears t o be a common mammalian response t o such environmental manipulations (Tees, 1990), and the a l t r i c i a l (immaturely born) r a t wit h i t s r a p i d p o s t - n a t a l n e u r a l and b e h a v i o r a l development time frame have made i t a u s e f u l animal model f o r c o n t r o l l e d r e a r i n g r e s e a r c h . For a v a r i e t y o f reasons, i n c l u d i n g the r e l a t i v e ease with which one can a l t e r e a r l y v i s u a l s t i m u l a t i o n h i s t o r y , the r o l e p l a y e d by ex p e r i e n c e i n the p h y s i o l o g i c a l and neuroanatomical development of the v i s u a l system and r e l a t e d b e h a v i o r s has been the prime f o c u s of much of the work u t i l i z i n g c o n t r o l l e d r e a r i n g paradigms (reviewed by Boothe, V a s s d a l , & Schenk, 1986; M i t c h e l l & Timney, 1984; Tees 1986, 1990). E l i m i n a t i n g a l l v i s u a l s t i m u l a t i o n by r e a r i n g i n complete darkness has been a common environmental m a n i p u l a t i o n . Many of the e f f e c t s o f d a r k - r e a r i n g are observed a t the l e v e l of the c o r t e x ( M i t c h e l l & Timney, 3 1984). In p a r t , d a r k - r e a r i n g l e a v e s the c o r t e x i n a " n o n s p e c i f i e d s t a t e " , which r e t a i n s c o n s i d e r a b l e c a p a c i t y f o r change when d a r k - r e a r i n g i s f o l l o w e d by a p e r i o d of v i s u a l s t i m u l a t i o n (Freeman, M a l l a c h , & H a r t l y , 1981). However, the exten t of p o t e n t i a l r e c o v e r y o f t e n becomes l e s s as the l e n g t h of d e p r i v a t i o n p e r i o d i n c r e a s e s . V i s u a l d e p r i v a t i o n appears t o l e a d t o some atrophy o f c o r t i c a l f u n c t i o n ( f o r review, see M i t c h e l l & Timney, 1984). B e h a v i o r a l l y , some a b i l i t i e s appear u n a f f e c t e d by dark-r e a r i n g . For example, no s i g n i f i c a n t d i f f e r e n c e s between l i g h t and dark r e a r e d animals have been found on t h e i r a b i l i t y t o r e s o l v e d e t a i l (Friedman & Green, 1982). Other a b i l i t i e s , however, are a f f e c t e d . On t e s t s o f depth p e r c e p t i o n , v i s u a l l y guided behavior, and form p e r c e p t i o n , the performance of dark r e a r e d r a t s i s g e n e r a l l y reduced i n comparison t o c o n t r o l animals (Tees, 1990). I t i s important t o note t h a t although the competence of dark r e a r e d r a t s i s a d v e r s e l y a f f e c t e d , i t i s not e l i m i n a t e d . For example, i n a t e s t o f depth p e r c e p t i o n , dark r e a r e d r a t s are a b l e t o d i s c r i m i n a t e between the shallow and deep s i d e s of a v i s u a l c l i f f p r o v i d e d the d i f f e r e n c e between the two s i d e s i s a t l e a s t 20 cm. They perform s i g n i f i c a n t l y worse than l i g h t -r e a r e d c o n t r o l s , o n l y when t e s t e d on s m a l l e r d i f f e r e n t i a l depths. Aspects of v i s u a l l y guided behaviors appear t o be pres e r v e d i n d a r k - r e a r e d r a t s i n s p i t e o f t h e i r l a c k of v i s u a l e x p e r i e n c e . For example, d a r k - r e a r e d r a t s e x h i b i t l e v e l s of l i g h t s e e k i n g b e h a v i o r comparable t o those o f l i g h t - r e a r e d r a t s 4 (Tees, Midgley, & Bruinsma, 1980). However, when more complex v i s u a l s t i m u l i are u t i l i z e d , d a r k - r e a r e d r a t s e x h i b i t some l a c k of o r i e n t a t i o n a l r esponsiveness over a wide p a r t of t h e i r v i s u a l f i e l d s (Midgley & Tees, 1983). A s p e c i f i c e f f e c t o f dark-r e a r i n g i s a l s o seen i n form p e r c e p t i o n . Although, d a r k - r e a r e d r a t s are as a b l e as l i g h t - r e a r e d r a t s t o i s o l a t e f i g u r e from ground (Tees, 1968), a c q u i r e v a r i o u s k i n d s o f d i s c r i m i n a t i o n s i n v o l v i n g d i f f e r e n c e s i n o r i e n t a t i o n of v i s u a l s t i m u l i (Tees, 1979), and g e n e r a l i z e along the dimension of angular o r i e n t a t i o n (Tees, 1972), such v i s u a l l y d e p r i v e d animals take much longer than l i g h t - r e a r e d c o n t r o l s t o l e a r n p a t t e r n d i s c r i m i n a t i o n s when the d i f f e r e n c e s between p a t t e r n s i n v o l v e r e l a t i o n a l p r o p e r t i e s between s e t s of l i n e s (Tees & Midgley, 1982). Unimodal r e s t r i c t i v e c o n t r o l l e d r e a r i n g has a l s o been u t i l i z e d e x t e n s i v e l y but more s e l e c t i v e l y i n r e s p e c t t o another sensory system, the somatosensory system. Although the somatosensory system has d i v e r s e i n p u t s from a v a r i e t y o f unique r e c e p t o r s t r u c t u r e s , most i n v e s t i g a t i o n s have focused on the r e c e p t o r s s t i m u l a t e d by the m y s t a c i a l v i b r i s s a e of rodents (Gustafson & Felbain-Keramidas, 1977; Kaas, Merzenich, & K i l l a c k e y , 1983). The m y s t a c i a l pad r e p r e s e n t s the s i n g l e l a r g e s t p o r t i o n o f the somatotopic map of the somatosensory c o r t e x o f the r a t ( F i g u r e 1). Receptors l o c a t e d w i t h i n the h a i r - f o l l i c l e o f each v i b r i s s a p r o j e c t c o n t r a l a t e r a l l y t o an i n d i v i d u a l f i e l d of c o r t i c a l c e l l s r e f e r r e d t o as a " b a r r e l " because of i t s d i s t i n c t i v e shape (Welker, 1976; Woolsey & Van Der Loos, 1970). A g r e a t d e a l of p h y s i o l o g i c a l and anatomical 5 evidence (Kaas e t a l . , 1983) has accumulated on the r e o r g a n i z a t i o n , or p l a s t i c i t y , t h a t takes p l a c e f o l l o w i n g e a r l y sensory r e s t r i c t i o n r e s u l t i n g from the c a u t e r i z a t i o n and removal of v i b r i s s a e i n new born animals. Such d e a f f e r e n t a t i o n prevents the development of the b a r r e l o r g a n i z a t i o n a t the c o r t i c a l l e v e l and t h e r e seems t o be a s e n s i t i v e p e r i o d f o r these e f f e c t s i n v o l v i n g a "window of time", p o s s i b l y c l o s i n g between post n a t a l days 7-10. Although v i b r i s s a e are thought t o p l a y an important r o l e i n the i n t e r a c t i o n s of the r a t w i t h i t s environment, the intermodal b e h a v i o r a l e f f e c t s of v i b r i s s a e removal have not been comprehensively documented. E a r l y r e s e a r c h r e v e a l e d few types of b e h a v i o r t h a t are guided s o l e l y by the v i b r i s s a e (Gustafson & Felbain-Keramidas, 1977), a r e s u l t t h a t i s s u r p r i z i n g i n l i g h t o f the anatomical and p h y s i o l o g i c a l evidence. Rats appear t o be a b l e t o adopt d i f f e r e n t b e h a v i o r a l s t r a t e g i e s t o compensate f o r v i b r i s s a e l o s s . Those behaviors f o r which v i b r i s s a e are c o n s i d e r e d important, such as t a c t i l e d i s c r i m i n a t i o n and s e v e r a l types of locomotion, have a l l , t o some degree, s u r v i v e d v i b r i s s a l removal (Keramidas, 1976). The removal of v i b r i s s a e has been shown t o decrease the s i z e of gap i n an e l e v a t e d runway t h a t a r a t w i l l jump a c r o s s (Hutson & Masterton, 1986). The v i b r i s s a e extend the reach of the r a t ; removing them decreases t h e i r c o n t a c t w i t h the surrounding environment and thus decreases t h e i r range of movement. In a more r e c e n t study, a b a t t e r y of sensorimotor t e s t s was used i n an attempt t o i l l u m i n a t e some of the b e h a v i o r a l e f f e c t s of e a r l y v i b r i s s a l 6 F i g u r e 1. The r e p r e s e n t a t i o n of v i b r i s s a e r e c e p t o r s by t h e i r c o r r e s p o n d i n g b a r r e l formations i n the c o n t r a l a t e r a l primary somatosensory c o r t e x ( P a r i ) of the r a t . 0c2ML Normal Barrels 7 removal (Symons & Tees, i n p r e s s ) . A l l e a r l y dewhiskered animals, r e g a r d l e s s of r e a r i n g c o n d i t i o n , d i s p l a y e d attenuated o r i e n t a t i o n t o l i g h t t a c t i l e s t i m u l a t i o n t o the m y s t a c i a l pads themselves. In a d d i t i o n t o intramodal consequences of unimodal d e p r i v a t i o n t h e r e has been renewed i n t e r e s t i n intermodal consequences of unimodal r e s t r i c t i o n . D i f f e r e n t i a l experience i n one m o d a l i t y c o u l d have consequences f o r the development and f u n c t i o n i n g of o t h e r sensory systems ( B u r n s t i n e , Greenough & Tees, 1984; G o t t l i e b , 1971; Turkewitz & Kenny, 1982). G o t t l i e b (1971) o u t l i n e d an i n v a r i a n t sequence i n which sensory systems develop i n v e r t e b r a t e s ( F i g u r e 2 ) . The t a c t i l e system becomes f u n c t i o n a l f i r s t , f o l l o w e d by the o l f a c t o r y and a u d i t o r y systems, wi t h the v i s u a l system coming on l i n e l a s t . Turkewitz and Kenny (1982) suggested t h a t t h i s sequence may f a c i l i t a t e the o r g a n i z a t i o n of sensory systems and p r o v i d e the b a s i s f o r subsequent p e r c e p t u a l development. Instead of having t o contend w i t h incoming i n f o r m a t i o n from a l l sensory systems a t once, neonates would d e a l w i t h l i m i t e d i n f o r m a t i o n r e l a t e d t o the sensory m o d a l i t i e s t h a t are f u n c t i o n a l a t t h a t stage i n development. T h i s f i l t e r i n g o f i n f o r m a t i o n c o u l d a l s o be observed w i t h r e s p e c t t o the nature of s i g n a l s w i t h i n a s i n g l e m o d a l i t y . When a system f i r s t becomes f u n c t i o n a l , the n e u r a l system i s r e l a t i v e l y p r i m i t i v e . G r a d u a l l y , the system evolves and i s a b l e t o encode and u t i l i z e p r o g r e s s i v e l y more complex i n f o r m a t i o n r e c e i v e d w i t h i n t h a t sensory m o d a l i t y . These l i m i t a t i o n s , r e s u l t i n g from the staggered onsets of sensory F i g u r e 2. The o n t o g e n e t i c sequence of emergence of sensory systems. (From G o t t l i e b , 1971). visual auditory olfactory vestibular somatosensory 9 systems, p r o v i d e an e v o l v i n g s t r u c t u r e i n t o which environmental s t i m u l a t i o n can be o r g a n i z e d (e.g. Tees 1990). D i f f e r e n t i a l onset of f u n c t i o n i n g i n each m o d a l i t y seems t o reduce c o m p e t i t i o n d u r i n g development and r e s u l t s i n r e l a t i v e independence between emerging systems (Turkewitz & Kenny, 1982). Competition, both i n t r a - and i n t e r m o d a l , has an important impact on n e u r a l and b e h a v i o r a l ontogenies. For example, i n k i t t e n s when one eye i s p l a c e d a t a c o m p e t i t i v e disadvantage through s u t u r i n g , the nondeprived eye expands i t s " t e r r i t o r y " i n t o the n e u r a l space t h a t normally r e c e i v e s s t i m u l a t i o n from the d e p r i v e d eye (Cynader 1979; Wiesel & Hubel 1963). A s i m i l a r expansion i s a l s o observed i n the somatosensory n e u r a l r e p r e s e n t a t i o n i n r a t s . E l i m i n a t i n g a row o r column of m y s t a c i a l v i b r i s s a e i n rodents l e a d s t o d i s r u p t i o n of normal b a r r e l f o r m a t i o n . The b a r r e l s of the a d j a c e n t i n t a c t v i b r i s s a e expand i n t o the n e u r a l space t h a t normally r e c e i v e s s t i m u l a t i o n from the c a u t e r i z e d v i b r i s s a e (Van Der Loos & Woolsey 1973). Turkewit2 and Kenny (1982) have suggested t h a t the e a r l i e r s tages of development of a system are c h a r a c t e r i z e d by i n c r e a s i n g c o m p e t i t i o n w i t h i n t h a t system and l i m i t e d c o m p e t i t i o n between d i f f e r e n t sensory systems. As a new sensory system comes "on l i n e " intermodal c o m p e t i t i o n becomes more p r e v a l e n t . During t h i s time, intermodal competencies may develop as a r e s u l t of such c o m p e t i t i o n . For example, with r e s p e c t t o n e u r a l development, Cynader (1979) found a decrease i n the number of c e l l s responding t o v i s u a l s t i m u l a t i o n i n the deep (multimodal) l a y e r s of the s u p e r i o r c o l l i c u l u s of the c a t 10 f o l l o w i n g dark r e a r i n g . Presumably, dark r e a r i n g would have put the v i s u a l system a t a c o m p e t i t i v e disadvantage t o the a u d i t o r y and somatosensory systems, a l l o w i n g these systems t o have a g r e a t e r i n f l u e n c e on the responding of c e l l s i n t h a t area, and take over groups of c e l l s f o r m e r l y r e s p o n s i v e t o the v i s u a l system. At the l e v e l of the c o r t e x , l i m i t i n g somatosensory or v i s u a l i n p u t can r e s u l t i n hypertrophy of areas r e p r e s e n t i n g o t h e r sensory m o d a l i t i e s . In another study, b l i n d i n g r a t s through e n u c l e a t i o n , or l i m i t i n g somatosensory i n p u t through c a u t e r i z a t i o n of v i b r i s s a e a t b i r t h , l e d t o an i n c r e a s e i n d e n d r i t i c s p i n e d e n s i t y i n the a u d i t o r y c o r t e x when examined a t 25 days p o s t n a t a l l y (Ryugo, Ryugo, Globus, & K i l l a c k e y 1975). The somatosensory c o r t e x of e n u c l e a t e d animals, and the v i s u a l c o r t e x of c a u t e r i z e d r a t s d i d not show a s i m i l a r i n c r e a s e . However, when long-term dewhiskered r a t s were s t u d i e d a t a more mature age (270 d a y s ) , t h e r e was evidence of a t h i c k e n i n g of the v i s u a l c o r t e x (Keramidas, 1976). There i s l i m i t e d evidence on the s i g n i f i c a n c e of intermodal c o m p e t i t i o n a t the b e h a v i o r a l l e v e l . K i t t e n s w i t h reduced t a c t i l e i n p u t through c l i p p i n g of v i b r i s s a e were found t o d i s c r i m i n a t e between shallow and deep s i d e s of a v i s u a l c l i f f a t younger ages and w i t h g r e a t e r c o n s i s t e n c y than c o n t r o l s (Turkewitz, G i l b e r t , & B i r c h , 1974). Rats t h a t experienced e a r l y somatosensory r e s t r i c t i o n by v i b r i s s a e c a u t e r i z a t i o n take l o n g e r t o h a b i t u a t e t o repeated v i s u a l s t i m u l i and are more l i k e l y t o o r i e n t a t e t o s u b t l e changes i n these s t i m u l i than are c o n t r o l r a t s (Symons & Tees, i n p r e s s ) . T h i s was t r u e o n l y f o r 11 animals r e a r e d w i t h d a i l y access t o an e n r i c h e d environment. In another study, long-term dewhiskered r a t s were f a s t e r t o a c q u i r e two v i s u a l d i s c r i m i n a t i o n s than were i n t a c t animals (Keramidas, 1976). F i n a l l y , b l i n d e d mice r a i s e d i n t a c t i l e e n r i c h e d e a r l y environments showed a v i b r i s s a e - t r i g g e r e d p l a c i n g response t o a g r e a t e r d i s t a n c e than d i d s i g h t e d c o n t r o l s . The normal p a t t e r n of c o m p e t i t i o n between d e v e l o p i n g systems can a l s o be a l t e r e d by the premature a v a i l a b i l i t y of i n f o r m a t i o n from a sensory system. Kenny and Turkewitz (1986) examined the e f f e c t s of e a r l y e y e l i d opening on the r a t pups' homing be h a v i o r . I n i t i a l l y , homing has been shown t o be under the c o n t r o l of thermal and o l f a c t o r y cues (Freeman & R o s e n b l a t t , 1978). F o l l o w i n g eye opening, v i s u a l o r i e n t a t i o n t o the home i s g r a d u a l l y developed. I n t e r e s t i n g l y , these phases match the developmental sequence of sensory m o d a l i t i e s . When v i s u a l i n f o r m a t i o n i s made a v a i l a b l e e a r l i e r t h a t normal through s u r g i c a l l y opening the e y e l i d s , homing behavior p e r s i s t s a t an age when i t normally d e c l i n e s (Kenny & Turkewitz, 1986). A v a i l a b i l i t y o f v i s u a l i n p u t b e f o r e thermal and o l f a c t o r y p a t t e r n s o f homing were e s t a b l i s h e d r e s u l t e d i n the development of an abnormal v i s u a l l y based p a t t e r n of homing. E a r l y eye opening a l s o a f f e c t e d l a t e r development o f the o l f a c t o r y system. Those pups r e c e i v i n g e a r l y v i s u a l exposure d i d not d i s c r i m i n a t e between shavings from the home cage and shavings w i t h d i f f e r e n t odors a t an age where t h e i r l i t t e r mate c o n t r o l s were making such d i s c r i m i n a t i o n s (Celenza, Kenny, & Turkewitz, 1984). 12 Ideas about modality interdependence, such as the ones outlined above, lead to two hypotheses regarding potential outcomes of any early r e s t r i c t i o n of, or damage to, one modality, on the subsequent development of the remaining i n t a c t modalities: 1) early r e s t r i c t i o n of sensory input i n one modality could r e s u l t i n intermodal compensation due to lack of competition from t h i s r e s t r i c t e d modality; 2) early r e s t r i c t i o n of sensory input into an early developing modality might disrupt the emerging organizational framework necessary for a competency which involves signals of a l a t e r developing modality. Evidence to support the f i r s t hypothesis has been presented above i n the discussion of competition. Limited behavioral support for the second hypothesis i s also a v a i l a b l e . For example, on a task of auditory l o c a l i z a t i o n , early blinded rats performed more poorly than l a t e blinded or sighted rats (Spigelman, 1969). Obviously, i n p a r t i c u l a r instances evidence for one of these hypotheses doesn't preclude the discovery of evidence f o r the other cases. P a r t i c u l a r competencies and sensory systems could be d i f f e r e n t i a l l y affected by the manipulations of early stimulation h i s t o r y (Tees, 1990). Presumably, because the somatosensory modality i s the f i r s t to develop, the impact of early r e s t r i c t i o n of t h i s modality could p o t e n t i a l l y be the greatest. As mentioned e a r l i e r , the co n t r o l l e d rearing paradigm has also been used by investigators who have focused on the e f f e c t s produced by multimodal complex rearing (Juraska, 1990; Rosenzweig & Bennett, 1977). Whereas r e s t r i c t i v e manipulations 13 are h y p o t h e s i z e d t o impede the development of p e r c e p t u a l competencies and b i a s e d r e a r i n g t o a l t e r i t i n a s p e c i f i c way, exposure t o a g e n e r a l complex environment i s t r a d i t i o n a l l y viewed as a c c e l e r a t i n g development. T y p i c a l l y , an complex environment c o n s i s t s of d a i l y exposure, i n groups, t o a l a r g e cage i n which t h e r e are a v a r i e t y of v i s u a l , t a c t i l e , and a u d i t o r y s t i m u l u s o b j e c t s f o r the animals t o i n t e r a c t w i t h . P o s i t i v e r e s u l t s from exposure t o a complex environment have been r e p o r t e d r e g a r d l e s s of the age a t which exposure o c c u r r e d ; however, the most dramatic e f f e c t s have r e s u l t e d from exposure d u r i n g the e a r l y developmental p e r i o d . In comparison t o r a t s r e a r e d under normal l a b o r a t o r y cage c o n d i t i o n s , r a t s r e a r e d i n e n r i c h e d environments show i n c r e a s e s i n the weight and t h i c k n e s s of the c o r t e x , i n the number of synapses and d e n d r i t i c s p i n e s per neuron, as w e l l as i n the o v e r a l l amount of d e n d r i t i c b r a n c h i n g i n the c o r t e x (Rosenzweig & Bennett, 1977). I n t e r e s t i n g l y , many of these same c e l l u l a r i n d i c e s decrease f o l l o w i n g dark r e a r i n g (Tees, 1990). However, the hypertrophy t h a t r e s u l t s from e a r l y complex r e a r i n g i s not seen i n a l l c o r t i c a l a r e a s . Dark r e a r i n g and complex r e a r i n g seem t o p r e f e r e n t i a l l y a f f e c t neurons i n the temporal and p a r i e t a l a s s o c i a t i o n c o r t e x , but not those i n the f r o n t a l c o r t e x (Greenough, Volkmar, & J u r a s k a , 1973). B e h a v i o r a l l y , r a t s r e a r e d i n a complex environment are s u p e r i o r t o c o n t r o l r a t s i n t h e i r performance on a v a r i e t y of t a s k s , i n c l u d i n g r e v e r s a l , a l t e r n a t i o n , and e s p e c i a l l y maze ( s p a t i a l ) t a s k s (Greenough & J u r a s k a , 1979). 14 B u m s t i n e e t a l . (1984) have argued t h a t i n c r e a s i n g environmental complexity augments ongoing b e h a v i o r a l demand. C l e a r l y , the demands p l a c e d on a s u b j e c t l i v i n g i n a l a b o r a t o r y environment are d i f f e r e n t from those e x i s t i n g f o r animals l i v i n g i n a n a t u r a l environment. B e h a v i o r a l d i f f e r e n c e s and d e f i c i e n c i e s might go u n n o t i c e d simply because the demands p l a c e d on the animal are not s u f f i c i e n t t o r e v e a l them. Intermodal compensation, and i t s r e l a t e d n e u r a l s u b s t r a t e s of f u n c t i o n a l r e a l l o c a t i o n and compensatory hypertrophy, r e s u l t i n g from d e p r i v a t i o n of one k i n d of sensory i n p u t , might be more e v i d e n t i n animal s t u d i e s with more demanding c o n d i t i o n s , both i n r e a r i n g environment and t e s t s i t u a t i o n ( B u r n s t i n e e t a l . , 1984; Tees, 1990). Whatever the u n d e r l y i n g mechanisms, i n c r e a s i n g b e h a v i o r a l demand would be an important i n v e s t i g a t i v e t o o l i n l o o k i n g a t the changes r e s u l t i n g from c o n t r o l l e d r e a r i n g s i t u a t i o n s . The degree t o which development of p e r c e p t u a l competencies was a l t e r e d by m a n i p u l a t i o n s of e a r l y experience i n c l u d i n g dewhiskering, dark r e a r i n g , and complex r e a r i n g , seems t o be more d i f f u s e than t h a t observed w i t h s p e c i f i c c o r t i c a l l e s i o n s (Tees, 1990). However, some modules seem more a f f e c t e d than o t h e r s (Table 1). The o p e r a t i o n s t h a t were v u l n e r a b l e t o changes i n e a r l y s t i m u l a t i o n h i s t o r y c o u l d be c h a r a c t e r i z e d as r e q u i r i n g t r a d e - o f f s between an a p p r e c i a t i o n of a s p e c t s of the environment and remembering s p e c i f i c f e a t u r e s w h i l e i g n o r i n g o t h e r s . These competencies seem t o i n v o l v e memory, a t t e n t i o n and a p p r e c i a t i o n of s p a t i a l a s p e c t s of the environment. In t h i s 15 Impact of Multimodal and Unimodal Environmental  M a n i p u l a t i o n s : B e h a v i o r a l Evidence* L i m i t e d E f f e c t C o n s i d e r a b l e E f f e c t 1. A b i l i t y t o r e s o l v e d e t a i l ( G r a t i n g s ) A b i l i t y t o r e c o g n i z e s t a t i o n a r y p a t t e r n s on the b a s i s o f r e l a t i o n s h i p between l i n e s (contour s e p a r a t i o n , contour i n t e r a c t i o n ) 2. A b i l i t y t o r e c o g n i z e v i s u a l s t i m u l i on the b a s i s o f angular o r i e n t a t i o n cues A b i l i t y t o a c q u i r e and remember s p a t i a l map of environment and t o na v i g a t e t o i n v i s i b l e t a r g e t s A b i l i t y t o o r i e n t (respond) t o e x t e r n a l movement A b i l i t y t o l o c a l i z e and respond t o l a r g e v i s u a l s t i m u l i A b i l i t y t o o r i e n t t o s p a t i a l and temporal changes i n p a t t e r n o r v i s u a l events 5. A b i l i t y t o r e c o g n i z e crossmodal a t t r i b u t e of d u r a t i o n and i n t e n s i t y of a u d i t o r y and v i s u a l events A b i l i t y t o r e c o g n i z e crossmodal a t t r i b u t e of l o c a t i o n o f a u d i t o r y and v i s u a l events * P a r t i a l l i s t o f competencies whose development i s a l t e r e d by multimodal complex r e a r i n g o r unimodal r e s t r i c t i v e r e a r i n g . The evidence supports the i d e a t h a t the impact of e a r l y s t i m u l a t i o n h i s t o r y i s l i m i t e d i n the case of the a b i l i t i e s l i s t e d on the l e f t where as i t i s c o n s i d e r a b l e i n the case of those l i s t e d on the r i g h t (from Tees, 1990). Table 1. D e s c r i p t i o n of the b e h a v i o r a l impact of multimodal and unimodal environmental m a n i p u l a t i o n s . 16 r e g a r d , l e s i o n s t u d i e s on the f u n c t i o n i n g of e x t r a s t r i a t e , p o s t e r i o r p a r i e t a l , and temporal c o r t e x suggest t h a t these c o r t i c a l r e g i o n s may be important t o the i n t e g r i t y of such competencies (Kolb, 1990). Our knowledge of the intermodal consequences of e a r l y unimodal r e s t r i c t i o n i s s e v e r e l y l i m i t e d . Although t h e r e i s l i m i t e d neuroanatomical support f o r both of the Turkewitz and Kenny (1982) hypotheses on the p o t e n t i a l outcomes o f e a r l y r e s t r i c t i o n of one modality, l i t t l e s u i t a b l e b e h a v i o r a l evidence e x i s t s . O b v i o u s l y , the anatomical and p h y s i o l o g i c a l d i f f e r e n c e s s hould be r e f l e c t e d i n b e h a v i o r a l d i f f e r e n c e s . More b e h a v i o r a l evidence i s r e q u i r e d f o r a c l e a r e r p i c t u r e of what c o r t i c a l o p e r a t i o n s are i n v o l v e d i n a r a t ' s p e r c e p t u a l r e a c t i o n s . One promising s t r a t e g y t o t e s t i d e a s about the t a r g e t of e x p e r i e n t i a l l y induced p l a s t i c i t y i s the d i r e c t use of s p e c i f i c s u r g i c a l i n t e r v e n t i o n i n c o n j u n c t i o n w i t h m a n i p u l a t i o n of e a r l y s t i m u l a t i o n h i s t o r y . In such an e f f o r t , we need t o focus on those s t r u c t u r e s t h a t b e h a v i o r a l (and n e u r a l ) evidence i n d i c a t e might be a l t e r e d s i g n i f i c a n t l y by c o n t r o l l e d r e a r i n g . In t h i s study we have focused on two areas of the p o s t e r i o r c o r t e x : somatosensory c o r t e x (Par 1) and e x t r a s t r i a t e c o r t e x (Oc2M). C o r t i c a l and s u b c o r t i c a l connections are shown i n F i g u r e 3. 1) Area Oc2M P a r t of area Oc2M a d j o i n s the medial border of O c l , and has a l s o been termed area 18, area 18b, o r medial p e r i s t r i a t e 17 F i g u r e 3. Connections of primary and secondary sensory r e g i o n s t o the p o s t e r i o r p a r i e t a l c o r t e x i n the r a t . (From Kolb, 1990). 18 c o r t e x . F u r t h e r r o s t r a l l y i t a d j o i n s the r o s t r o m e d i a l boundary of Ocl and t h e r e seems t o correspond b e t t e r w i t h p a r t of p o s t e r i o r p a r i e t a l c o r t e x (area 7 ) . Area 0c2M r e c e i v e s a p r o j e c t i o n from O c l and from the l a t e r a l p o s t e r i o r nucleus (Dean, 1990). Two v i s u a l maps are c o n t a i n e d w i t h i n the area, both o f which emphasize the p e r i p h e r a l f i e l d (Espinoza & Thomas, 1983; O l a v a r r i a & Montero, 1984). The p r e c i s e r o l e o f area 0c2M i n r a t s can p r e s e n t l y o n l y be s p e c u l a t e d on (Dean, 1990). In the m a j o r i t y o f l e s i o n s t u d i e s area Oc2M i s not removed alone, but as p a r t of l a r g e r l e s i o n s i n combination w i t h o t h e r c o r t i c a l v i s u a l areas. However, when area Oc2M i s i n c l u d e d i n a g i v e n l e s i o n , b e h a v i o r a l d e f i c i t s appear on two types of t a s k s : those i n v o l v i n g response t o t r a n s i e n t (suddenly appearing o r moving) s t i m u l i and those i n v o l v i n g a n a l y s i s o f p e r i p h e r a l s p a t i a l cues f o r n a v i g a t i o n . Midgley and Tees (1981) found p o s t e r i o r c o r t e x l e s i o n s , i n c l u d i n g area Oc2M, reduced r e s p o n s i v e n e s s t o p a t t e r n s of l i g h t f l a s h e s . L e s i o n i n g areas O c l , 0c2M, and Oc2L t o g e t h e r produced d i f f i c u l t y i n d e t e c t i n g l i g h t onset, both p e r i p h e r a l l y and c e n t r a l l y (Overton c i t e d i n Dean, 1986). Recent f i n d i n g s (Overton & Dean, i n pr e s s ) suggest t h a t l e s i o n s removing o n l y area 0c2M may reduce s e n s i t i v i t y t o dim l i g h t f l a s h e s . In another study where o n l y area 0c2M was l e s i o n e d , r a t s were a b l e t o l e a r n a b r i g h t n e s s d i s c r i m i n a t i o n , but a c q u i s i t i o n of a bla c k - w h i t e p a t t e r n d i s c r i m i n a t i o n was r e t a r d e d (McDaniel & T e r r e l l W a l l , 1988). 19 Both Goodale and Dale (1981) and Foreman and Stevens (1982) found l a r g e l e s i o n s t o the p o s t e r i o r p a r i e t a l c o r t e x t o impair l e a r n i n g on the r a d i a l arm maze s p a t i a l t a s k . Smaller p o s t e r i o r p a r i e t a l l e s i o n s , which i n c l u d e d both the r o s t r a l p o r t i o n of 0c2M and 0c2L produced d e f i c i t s on both the water maze and the r a d i a l arm maze (Kolb & Walkey, 1987). More s p e c i f i c l e s i o n s which i n c l u d e d o n l y area 0c2M r e s u l t e d i n impaired performance by l e s i o n e d animals on the normal M o r r i s water maze procedure as w e l l as on the landmark v e r s i o n of the water maze ta s k (Kolb, p e r s o n a l communication). Area 0c2M may a l s o f u n c t i o n t o i n t e g r a t e s p a t i a l cues from d i f f e r e n t m o d a l i t i e s . F o l l o w i n g b i l a t e r a l removal of area 0c2M, Pinto-Hamuy, O l v a r r i a , G u i c -Robles, Morgues, N a s s a l , and P e t i t (1987) found t h a t r a t s were unable t o d i s c r i m i n a t e between p a i r s of compound v i s u a l and somatic s t i m u l i . 2) Area Par 1 Primary somatosensory c o r t e x , area Par 1, c o n t a i n s a somatotopic r e p r e s e n t a t i o n or map of the r a t ' s body. I t i s l o c a t e d a n t e r i o r t o v i s u a l c o r t e x , a d j a c e n t t o and a c t u a l l y p a r t i a l l y o v e r l a p p i n g the motor c o r t e x . Par 1 appears t o be s e l e c t i v e f o r performance i n sensory t a s k s which r e q u i r e an a c t i v e movement component (Chapin & L i n , 1990). Hudson and Masterton (1986) found t h a t the a b i l i t y o f the r a t t o c o l l e c t s i t u a t i o n - r e l e v a n t i n f o r m a t i o n w i t h i t s v i b r i s s a e i s l o s t a f t e r the a b l a t i o n of the c o r r e s p o n d i n g c o r t i c a l b a r r e l s . In t h e i r study, r a t s would jump a gap i n an e l e v a t e d runway a f t e r p a l p a t i n g the f a r s i d e w i t h t h e i r v i b r i s s a e o n l y when 20 c o n t r a l a t e r a l Par 1 remained i n t a c t . In a d d i t i o n , damage t o t h i s area appears t o impair performance on t a s k s of p a l p i t a t i o n , h a p t i c e x p l o r a t i o n , a c t i v e touch, t a c t i l e p l a c i n g , and hopping (Chapin & L i n , 1990). In e f f e c t , area Par 1 i s thought t o be the s i g h t o f an i n t e g r a t i o n of i n f o r m a t i o n from cutaneous and p r o p r i o c e p t i v e somatosensory s u b m o d a l i t i e s w i t h i n f o r m a t i o n from the motor c o r t e x . As mentioned e a r l i e r , complex r e a r i n g and dark r e a r i n g seem t o a f f e c t f u n c t i o n s i n which e x t r a s t r i a t e c o r t e x would p l a y a s i g n i f i c a n t r o l e . As f a r as dewhiskering i s concerned, s u b s t a n t i a l c o r t i c a l changes are observed i n Par l wit h e a r l y dewhiskering; thus a s u r g i c a l i n t e r v e n t i o n t h a t i t s e l f f o c uses on t h i s r e g i o n c o u l d p r o v i d e i n t e r e s t i n g i n f o r m a t i o n . W i l l s e l e c t i v e l e s i o n s o f these c o r t i c a l r e g i o n s have more of an impact on d a r k - r e a r e d than on complex-reared? We c e r t a i n l y know t h a t p r e o p e r a t i v e environments do have an e f f e c t on the impact of non-sensory c o r t i c a l l e s i o n s and r e l a t e d t a s k s (Kolb 1990). W i l l Oc2M l e s i o n s have l e s s of an impact on d a r k - r e a r e d than l i g h t - r e a r e d animals? The evidence suggests t h a t the combination of d a r k - r e a r i n g and s u p e r i o r c o l l i c u l u s l e s i o n s (which p r o j e c t s t o e x t r a s t r i a t e c o r t e x ) , but not the combination of dark r e a r i n g and O c l l e s i o n s , has a s e r i o u s impact f o r the development of visuomotor o r i e n t a t i o n s k i l l s ( F i n d l a y , Marder, & Cordon, 1980). In l o o k i n g a t the impact of e a r l y d e v e l o p i n g m o d a l i t i e s w i t h r e s p e c t t o a l a t e r d e v e l o p i n g one, the somatosensory system i s an i d e a l c a n d i d a t e i f dewhiskering does 21 have intramodal consequences. Exposure t o complex r e a r i n g ( i e . i n c r e a s i n g b e h a v i o r a l demand), sh o u l d i l l u m i n a t e or augment the e f f e c t s of e a r l y somatosensory and/or v i s u a l r e s t r i c t i o n and produce the g r e a t e s t p o t e n t i a l f o r evidence of intermodal compensation. Removal of area 0c2M w i l l a l s o serve t o h e l p d e l i n e a t e the s p e c i f i c f u n c t i o n s of t h i s a r e a . In o r d e r t o assess the consequences of e a r l y experience and s e l e c t i v e c o r t i c a l l e s i o n s , a b a t t e r y of f i v e t e s t s was used. These t e s t s encompassed both s p e c i e s s p e c i f i c and l e a r n e d b e h a v i o r s . The t h r e e s p e c i e s s p e c i f i c t a s k s were p a r t of a s h o r t t e s t b a t t e r y t h a t was a d m i n i s t e r e d p o s t - o p e r a t i v e l y . There i s some evidence t o i n d i c a t e t h a t f o l l o w i n g e a r l y c o r t i c a l l e s i o n s , s p a r i n g of f u n c t i o n i s more common on l e a r n i n g t a s k s than on t e s t s of s p e c i e s t y p i c a l b e h a v i o r (Kolb & Whishaw, 1989). T h i s i s p o s s i b l y because on many t e s t s of l e a r n i n g , more than one s t r a t e g y can be used. The t e s t s of s p e c i e s t y p i c a l b e h a v i o r s are i n c l u d e d i n t h i s study t o determine i f the impact of e a r l y sensory d e p r i v a t i o n on these b e h a v i o r s i s s i m i l a r t o t h a t of e a r l y c o r t i c a l l e s i o n s . Tasks i n c l u d e d were measures of grooming beh a v i o r , p r o t e c t i o n of food, and e x p l o r a t i o n of novel o b j e c t s i n the environment. The two l e a r n i n g t a s k s were s e l e c t e d on the b a s i s of being s e n s i t i v e t o p o s t e r i o r p a r i e t a l c o r t e x f u n c t i o n . A v a r i a t i o n of the M o r r i s Water Maze ta s k , developed by Symons and Tees ( i n p r e s s ) , was used t o assess s p a t i a l memory. V a r i a t i o n s of t h i s t a s k have been used t o assess the e f f e c t s of v a r i o u s b r a i n l e s i o n s (Kolb & Walkey, 1987), and the ontogeny of s p a t i a l 22 behavior (Rudy, S t a d l e r - M o r r i s , & A l b e r t , 1987). In t h i s t a s k r a t s are r e q u i r e d t o f i n d a submerged p l a t f o r m hidden i n a pool of water u s i n g the a v a i l a b l e proximal and d i s t a l cues. T h i s task w i l l a s s ess d i f f e r e n c e s i n v i s u a l s p a t i a l b ehavior caused by d i f f e r e n c e s i n r e a r i n g c o n d i t i o n and s p e c i f i c l e s i o n s . To e v a l u a t e v i s u a l discrimination/memory, a second v a r i a t i o n of the M o r r i s Water Maze was used. Again, r a t s are r e q u i r e d t o f i n d a submerged p l a t f o r m . However, i n t h i s v e r s i o n , the l o c a t i o n of the p l a t f o r m i s s i g n a l e d by proximal cues of d i f f e r e n t p a t t e r n s . S u c c e s s f u l d i s c r i m i n a t i o n o f , and memory f o r , two p a i r s of cues i s r e q u i r e d t o l o c a t e the p l a t f o r m . An i n c r e a s e i n d e n d r i t i c a r b o r i z a t i o n has been c o r r e l a t e d w i t h enhanced b e h a v i o r a l a b i l i t i e s f o l l o w i n g complex r e a r i n g (Rosenzweig & Bennett, 1977), as w e l l as w i t h s p a r i n g of f u n c t i o n f o l l o w i n g e a r l y c o r t i c a l damage (Kolb, 1989, Kolb & Whishaw, 1989). In order t o a s sess the e f f e c t of e a r l y r e a r i n g environment on c o r t i c a l d e n d r i t i c branching, b r a i n s of c o n t r o l animals from each r e a r i n g c o n d i t i o n were s t a i n e d by the G o l g i -Cox method ( G l a s e r & Van Der Loos, 1981; Kolb & McClimmons, 1986). C e l l s from somatosensory, v i s u a l , and a u d i t o r y c o r t e x were drawn and analyzed. 23 Methods Su b j e c t s The s u b j e c t s were 84 male r a t s , from 19 l i t t e r s , of the Long-Evans (Rattus Norvegicus) s t r a i n , born and r e a r e d a t the biopsychology c o l o n i e s a t the U n i v e r s i t y o f B r i t i s h Columbia. The g e n e r a l r e a r i n g c o n d i t i o n s have been d e s c r i b e d p r e v i o u s l y (Tees, 1968). The r a t s were r a i s e d i n p l a s t i c m a t e r n i t y b i n s , (25 x 47 x 20 cm), u n t i l 21 days of age. At t h i s time they were weaned and p l a c e d i n groups of 3-6 i n hanging wire mesh cages (66 x 25 x 18 cm). Ad l i b i t u m food ( P u r i n a Rat Chow) and water were a v a i l a b l e . At the time of t e s t i n g , r a t s were separated i n t o s i n g l e hanging mesh wire cages (20 x 25 x 18 cm). T e s t i n g began a t approximately 100 days of age. A l l r a t s weighed between 350 and 500 g a t the time of t e s t i n g . Environments and Rearing conditions Beginning on p o s t - n a t a l day 1-3, h a l f o f the animals (42 r a t s from nine l i t t e r s ) were a s s i g n e d t o be r e a r e d i n complete darkness. C o n d i t i o n s f o r dark r e a r i n g have been d e s c r i b e d p r e v i o u s l y (Tees, 1968). Dark-reared (DR) animals remained i n dark c o n d i t i o n s f o r the d u r a t i o n o f the study. The remaining animals (42 r a t s from t e n l i t t e r s ) were r e a r e d i n the l i g h t and g i v e n e n r i c h e d (complex) (CR) r e a r i n g e x p e r i e n c e . The unique environmental c o n d i t i o n s f o r complex r e a r e d s u b j e c t s began a t 20 days of age. Exposure c o n t i n u e d f o r a minimum of two hours a day u n t i l t he animals were 49 days o f 24 age. T h i s d a i l y p e r i o d of e n r i c h e d environmental exposure has been r e p o r t e d t o be as e f f e c t i v e as long exposure, a t l e a s t i n terms of many n e u r a l and b e h a v i o r a l measures (Rosenzweig & Bennett, 1977; Rosenzweig, Love, & Bennett, 1968). The complex environment c o n s i s t e d of a t a l l , wire mesh chamber (180 x 92 x 62 cm) w i t h a S a n i c e l covered f l o o r and two S a n i c e l covered b r i d g e s , l o c a t e d approximately 20 and 40 cm above the f l o o r . Wire mesh ramps connected the b r i d g e s w i t h one another and with the bottom of the chamber. The environment was f i l l e d w i t h an assortment of t o y s and o b j e c t s of v a r y i n g s i z e s , shapes, and t e x t u r e s , some of which a l s o produced n o i s e when manipulated by the animals. O b j e c t s were changed and moved around d a i l y (Greenough & Green, 1981). Hanging from the s h e l v e s , ramps, and c e i l i n g were b e l l s and chimes which a l s o produced sound when co n t a c t e d . Two such environments e x i s t e d . Groups were p l a c e d i n each f i e l d on a l t e r n a t i n g days. Complex r e a r e d animals maintained a 12:12 hour l i g h t / d a r k schedule throughout the experiment. B e h a v i o r a l t e s t i n g was performed d u r i n g the animals' l i g h t c y c l e . Syrgery One h a l f of both the dark r e a r e d and complex r e a r e d animals underwent complete removal of t h e i r m y s t a c i a l v i b r i s s a e through c a u t e r i z a t i o n of the v i b r i s s a e f o l l i c l e s . In o r d e r t o ensure t h a t v i b r i s s a e removal occurs b e f o r e the i n i t i a l development of the p o s t eromedial b a r r e l f i e l d a l l animals were operated on w i t h i n 3 days of b i r t h (Kerimidas, 1976). To a v o i d p l a c i n g 25 dewhiskered pups a t a c o m p e t i t i v e disadvantage i n comparison t o i n t a c t l i t t e r m a t e s , animals were a s s i g n e d t o undergo the c a u t e r i z a t i o n procedure by l i t t e r . L i t t e r s were assig n e d randomly. F i v e l i t t e r s i n the l i g h t r e a r e d c o n d i t i o n (21 r a t s ) and f i v e l i t t e r s i n the dark r e a r e d c o n d i t i o n (21 r a t s ) underwent c a u t e r i z a t i o n . Pups were separated from t h e i r dams and a n e s t h e t i z e d w i t h a combination o f c o l d ( i c e ) and Halothane vapor. Animals were then maintained on i c e d u r i n g . s u r g e r y . Each v i b r i s s a was i n d i v i d u a l l y l o c a t e d with a d i s s e c t i n g microscope. A t h i n (98 micrometer) wire connected t o a DC l e s i o n maker (Grass) was i n s e r t e d i n t o the f o l l i c l e . The f o l l i c l e was then l e s i o n e d u s i n g a 150 V c u r r e n t w i t h an i n t e n s i t y o f 2 ma (Van Der Loos & Woolsey, 1973). The wire r e p r e s e n t e d the n e g a t i v e source while the p l a t e the animal r e s t e d on d u r i n g the surgery was the p o s i t i v e source. C o n t r o l animals were a n e s t h e t i z e d as w e l l , but the c a u t e r i z a t i o n p rocess was omi t t e d . A l l pups were warmed t o normal body temperature b e f o r e b e i n g r e t u r n e d t o t h e i r dams i n t h e i r home cages. At 90 days of age r a t s underwent a second s e t of s u r g i c a l i n t e r v e n t i o n s . Animals were randomly a s s i g n e d a c r o s s l i t t e r s t o one o f two l e s i o n groups or t o the l e s i o n c o n t r o l group. Rats were a n e s t h e t i z e d u s i n g sodium p e n t o b a r b i t a l (100 mg/kg i.p.) and operated on under s t e r i l e c o n d i t i o n s . The p a r i e t a l c o r t e x l e s i o n s were intended t o b i l a t e r a l l y remove the area c o n t a i n i n g the b a r r e l f i e l d s (Par 1). A s k u l l opening was made from 1.5 mm t o 3 mm p o s t e r i o r t o bregma, and from 3 mm t o 7 mm l a t e r a l from 26 the m i d l i n e . The exposed b r a i n was removed through a s p i r a t i o n . The e x t r a s t r i a t e c o r t e x l e s i o n s were intended t o b i l a t e r a l l y remove area 0c2M ( Z i l l e s , 1990). The s k u l l opening was made from 3 mm t o 7 mm p o s t e r i o r t o bregma, and from 1.5 mm t o 3 mm l a t e r a l from the m i d l i n e . C o n t r o l animals were a n e s t h e t i z e d and the s k i n i n c i s e d and s u t u r e d . Surgery was f o l l o w e d by a one week re c o v e r y p e r i o d . The d i f f e r e n c e s i n e a r l y r e a r i n g c o n d i t i o n s combined wi t h the e a r l y s u r g i c a l i n t e r v e n t i o n ( c a u t e r i z a t i o n ) r e s u l t e d i n f o u r i n i t i a l experimental groups. The groups were as f o l l o w s : CR normal, CR c a u t e r i z e d , DR normal, DR c a u t e r i z e d . There were 21 animals i n each group. Animals from these o r i g i n a l f o u r groups were then randomly a s s i g n e d t o one of the t h r e e " s u r g i c a l " c o n d i t i o n s : 0c2M, Par 1, or c o n t r o l . The g e n e r a l d e s i g n of the study was a 4 x 3 f a c t o r i a l . The f o u r environment types r e p r e s e n t e d one f a c t o r and s u r g i c a l o r l e s i o n c o n d i t i o n the second. Thus, as shown i n F i g u r e 4, the f i n a l d e s i g n had 12 experimental groups, w i t h seven r a t s i n each group. B e h a v i o r a l Tasks The e f f e c t s o f e a r l y r e a r i n g and l e s i o n s on the animals were b e h a v i o r a l l y assessed by a v a r i e t y of s p e c i e s s p e c i f i c and d i s c r i m i n a t i o n t a s k s . Species s p e c i f i c b e h a v i o r s were examined through a s h o r t t e s t b a t t e r y a d m i n i s t e r e d f o l l o w i n g r e c o v e r y from s u r g e r y , a t approximately 100 days of age. The b a t t e r y c o n s i s t e d of t h r e e separate t a s k s : grooming, dodging and 27 F i g u r e 4. Design of the experimental groups i n c l u d e d i n the study. t Goirit FG l i * FG FG 28 wrenching, and a v i s u a l / t a c t i l e d i s c r i m i n a t i o n t a s k . A l l t e s t s i n the b a t t e r y were g i v e n i n the same t e s t i n g room, over a p e r i o d of 4 days. The grooming, v i s u a l / t a c t i l e d i s c r i m i n a t i o n and dodging and wrenching t a s k s were a l l t e s t e d i n the same c y l i n d r i c a l , P l e x i g l a s s chamber. The c y l i n d e r was 50 cm deep wi t h a diameter of 50 cm. The r a t s were h a b i t u a t e d t o the c y l i n d e r and the t e s t room i n d i v i d u a l l y f o r a t l e a s t two 15 minute s e s s i o n s i n the days p r i o r t o t e s t i n g . Short T e s t B a t t e r y 1) grooming Rats were submersed i n water t o thoroughly wet t h e i r f u r and then p l a c e d i n the p r e v i o u s l y d e s c r i b e d chamber. Animals were then v i d e o t a p e d f o r 5 minutes. Videotapes were score d f o r the number of grooming sequences, the number of grooming components, and the t o t a l d u r a t i o n of grooming (Whishaw, Kolb, & S u t h e r l a n d , 1983). 2) Dodging and Wrenching The dodging and wrenching paradigm was o r i g i n a l l y developed by Whishaw and Tomie (1987) as a measure of a n a t u r a l l y o c c u r r i n g b e h a v i o r observed when r a t s are group-housed. B a s i c a l l y , i t i n v o l v e s c o m p e t i t i o n f o r a l i m i t e d amount of food. A r a t without food w i l l attempt t o s t e a l (rob) food from a r a t w i t h food. The r a t w i t h food w i l l attempt t o p r o t e c t i t by dodging away. A normal dodge i s when the r a t t u r n s away 180 degrees c o n t r a l a t e r a l t o the approaching robber. Besides the 29 normal dodge, t h e r e are s e v e r a l o t h e r l e s s f r e q u e n t l y o c c u r r i n g responses t o a robbery attempt. The v i c t i m can t w i s t away (a c o n t r a l a t e r a l dodge of l e s s than 180 degrees), run forward, k i c k the approaching robber, or backward dodge (a dodge over and around the r o b b e r ) . A f i n a l response i s the u n s u c c e s s f u l p r o t e c t i o n of the food p e l l e t r e s u l t i n g i n a robbery. Rats were food d e p r i v e d o v e r n i g h t t o ensure t h a t they were motivated t o p r o t e c t the food a t the time of t e s t i n g . Two animals were then p l a c e d i n the t e s t i n g chamber t o g e t h e r and one was g i v e n a p e l l e t of food ( P u r i n a Rat Chow). The f i r s t t e n responses of the r a t w i t h the food p e l l e t t o the approach of the robber were vid e o t a p e d . Responses were c a t e g o r i z e d as one of 6 p o s s i b l e responses, and the frequency of the normal dodge was compared t o the frequency o f a l l o t h e r responses. 3) V i s u a l and T a c t i l e "Novelty" D i s c r i m i n a t i o n A v e r s i o n of t h i s t a s k was r e c e n t l y d e s c r i b e d by Ennanceur and Delacour (1988). T h i s t a s k i s p r e d i c a t e d on the f a c t t h a t r a t s normally p r e f e r n o vel s t i m u l i . When presented w i t h two o b j e c t s , one n o v e l , the other f a m i l i a r , the r a t w i l l tend t o spend more time e x p l o r i n g the n o v e l o b j e c t . T h i s i n d i c a t e s t h a t they remember the o r i g i n a l o b j e c t and are a b l e t o d i s t i n g u i s h i t from the novel o b j e c t . In our v e r s i o n of the t a s k t h e r e were two separate d i s c r i m i n a t i o n s t e s t e d , one v i s u a l , the second t a c t i l e . Rats were exposed f o r t h r e e minutes t o a p a i r o f i d e n t i c a l o b j e c t s , i n the c y l i n d r i c a l , P l e x i g l a s s chamber used i n p r e v i o u s 30 t e s t i n g . They were then removed f o r a 60 second i n t e r - t r i a l i n t e r v a l , and then were g i v e n a second t h r e e minute t e s t . Exposure d u r i n g t h i s p e r i o d was t o a "mixed" p a i r of o b j e c t s , one of which was i d e n t i c a l t o the two o b j e c t s used i n the f i r s t t r i a l , w h i le the oth e r was a new o b j e c t t o which the r a t had not p r e v i o u s l y been exposed. The o b j e c t s themselves were made of wood, and f o u r exemplars of each d i f f e r e n t o b j e c t were used. For the v i s u a l v e r s i o n of the t a s k o b j e c t s were d i f f e r e n t t h r e e - d i m e n s i o n a l shapes: i s o s c e l e s t r i a n g l e s and c y l i n d e r s . A l l o b j e c t s i n t h i s group were p a i n t e d b l u e and had the same o v e r a l l s u r f a c e area and volume. The o b j e c t s used f o r the t a c t i l e d i s c r i m i n a t i o n were two-inch cubes. Four exemplars are smooth s u r f a c e d and the remaining f o u r , rough s u r f a c e d . The rough s u r f a c e was achieved by g l u e i n g sand onto a l l s i d e s . A l l cubes, smooth and rough were subsequently p a i n t e d ( b l a c k ) . To e l i m i n a t e o l f a c t o r y cues an o b j e c t was used i n o n l y one t r i a l f o r each r a t and a l l o b j e c t s were washed a f t e r each use. The two d i s c r i m i n a t i o n t e s t s were g i v e n over two c o n s e c u t i v e days. The order of the t a s k s was v a r i e d randomly: h a l f the r a t s were presented the v i s u a l d i s c r i m i n a t i o n t a s k f i r s t , w h i l e the remainder the t a c t i l e d i s c r i m i n a t i o n t a s k . The p r e s e n t a t i o n of o b j e c t s w i t h i n each t a s k was a l s o randomly v a r i e d . The amount of time spent e x p l o r i n g each o b j e c t on each t e s t was measured. Behavior was i d e n t i f i e d as e x p l o r a t o r y when the nose was a t a d i s t a n c e of 2 cm o r l e s s t o the o b j e c t , o r when the v i b r i s s a e were i n c o n t a c t w i t h the o b j e c t . The r a t i o 31 of t o t a l time spent e x p l o r i n g the new o b j e c t t o t o t a l time spent e x p l o r i n g the o l d o b j e c t was c a l c u l a t e d and recorded. Water-Based S p a t i a l Memory Task A p r o c e d u r a l v a r i a t i o n of the water maze t a s k developed by M o r r i s (1981) was used t o e v a l u a t e s p a t i a l memory. The apparatus c o n s i s t e d of a white, c i r c u l a r f i b e r g l a s s pool with a diameter of 1.8 meters and a depth of 60 cm. The p o o l was f i l l e d t o 35 cm w i t h water a t room temperature (approximately 21 degrees C). White w a t e r c o l o r p a i n t was added t o the water t o make i t opaque. The p l a t f o r m was a l a r g e p l a s t i c j a r , 32 cm t a l l and 9 cm i n diameter a t the l i d . Wire mesh was a t t a c h e d t o the t o p of the j a r and the j a r was f i l l e d w i t h stones f o r weight. The e n t i r e p l a t f o r m s t r u c t u r e was p a i n t e d white t o render i t i n v i s i b l e i n the opaque water. A b l u e racquet b a l l (Deuce Court) p a i n t e d with white s t r i p e s was used as a proximal cue and was a t t a c h e d by a 30 cm s t r i n g t o a sheet metal anchor. T h i s allowed the cue t o be p l a c e d on the p l a t f o r m or t o f l o a t f r e e l y depending on the nature of the t r i a l . The e n t i r e apparatus r e s i d e d i n a t e s t i n g room wi t h a number of conspicuous d i s t a l cues a v a i l a b l e . The t e s t i n g c o n s i s t e d of 18 t r i a l s conducted over t h r e e days. A summary of t r i a l s i s shown i n Table 2. On the f i r s t day each r a t was g i v e n two 90 sec h a b i t u a t i o n t r i a l s w i t h no p l a t f o r m (P) or cue (C) p r e s e n t . On the second day, t e s t i n g began. The second day c o n s i s t e d of e i g h t t r i a l s . For the f i r s t f o u r t r i a l s , the p l a t f o r m i s l o c a t e d i n quadrant 1 (North West) 32 t r i a l number t r i a l type d e s c r i p t i o n 1 C l / P l Cue l o c a t e d on t o p of quadrant 1 (northwest) p l a t f o r m • i n 2 C l / P l Cue l o c a t e d on top of p l a t f o r m i n Q l . 3 C l / P l Cue l o c a t e d on t o p of p l a t f o r m i n Q l . 4 C l / P l Cue l o c a t e d on top of p l a t f o r m i n Q l . 5 C3/P1 Cue l o c a t e d i n quadrant 3 ( s o u t h e a s t ) . P l a t f o r m i n quadrant 1 (northwest). 6 C3/P1 Cue i n Q3. P l a t f o r m i n Q l . 7 C3/P1 Cue i n Q3. P l a t f o r m i n Q l . 8 C3/P1 Cue i n Q3. P l a t f o r m i n Q l . 9 C3/P3 Cue l o c a t e d on t o p of p l a t f o r m i n quadrant 3. 10 C3/P3 Cue on top of p l a t f o r m i n Q3 • 11 C3/P3 Cue on top of p l a t f o r m i n Q3 • 12 C3/P3 Cue on top of p l a t f o r m i n Q3 • 13 -/P3 No cue. P l a t f o r m l o c a t e d i n Q3. 14 -/P3 No cue. P l a t f o r m l o c a t e d i n Q3. 15 -/P3 No cue. P l a t f o r m l o c a t e d i n Q3. 16 -/P3 No cue. P l a t f o r m l o c a t e d i n Q3. Table 2. D e s c r i p t i o n of the t r i a l s i n the Water-Based S p a t i a l L e a r n i n g Task 33 and the proximal cue i s p l a c e d on top of i t . On t r i a l s 5-8, the cue i s p l a c e d i n quadrant 3 (South East) w h i l e the p l a t f o r m remains i n quadrant 1. On the second day of t e s t t r i a l s 9-16 were run. For t r i a l s 9-12 the p l a t f o r m was moved beneath the cue i n quadrant 3. On t r i a l s 13-16 the cue was removed from the p o o l . The animals were r e l e a s e d on each t r i a l from one of the f o u r p o l e s i n a pseudorandom sequence. Escape l a t e n c y was rec o r d e d . Whether or not animals touched the cue d u r i n g t r i a l s 5-8, when the cue was l o c a t e d i n an " i n c o r r e c t " quadrant, was a l s o r e c o r d e d . The e n t i r e t r i a l was videotaped f o r a f u r t h e r more d e t a i l e d a n a l y s i s of b e h a v i o r . When a r a t encountered the p l a t f o r m , i t was p e r m i t t e d t o remain t h e r e f o r 10 seconds. I f the p l a t f o r m was not l o c a t e d w i t h i n 90 seconds the t r i a l was terminated, and the r a t removed and g i v e n a s c o r e of 90 seconds. Water-Based Concurrent V i s u a l D i s c r i m i n a t i o n Task A second v a r i a t i o n o f the M o r r i s Water Maze was used t o e v a l u a t e v i s u a l discrimination/memory per se (Kolb, Buhrmann & McDonald, 1989). The apparatus and p l a t f o r m were the same as used f o r the s p a t i a l memory t a s k . Four a i r f i l l e d rubber b a l l s , approximately 10 cm i n diameter were p a i n t e d i n d i f f e r e n t p a t t e r n s i n b l a c k and white and used as the cues w i t h which t o l e a r n the t a s k . The f o u r s t i m u l i were presented i n p a i r s of two. In p a i r one the p o s i t i v e cue, (the cue s i g n a l l i n g the l o c a t i o n of the p l a t f o r m ) , was white w i t h l a r g e b l a c k s p o t s , 34 while the n e g a t i v e cue had b l a c k and white h o r i z o n t a l s t r i p e s approximately 1.5 cm wide. In the second p a i r the p o s i t i v e cue had b l a c k and white v e r t i c a l s t r i p e s one c e n t i m e t e r wide w h i l e the n e g a t i v e cue was s o l i d grey. T r a i n i n g c o n s i s t e d of 80 t r i a l s run over 10 days. Over the e i g h t t r i a l s i n each t e s t day, each p a i r of s t i m u l i was used on a l t e r n a t e t r i a l s . L o c a t i o n of the p o s i t i v e cue (escape p l a t f o r m ) and the n e g a t i v e cue were randomly switched between quadrants t h r e e (South East) and f o u r (South West) of the p o o l . On each t e s t day the p l a t f o r m was i n each quadrant an equal number of times. Release p o i n t on each t r i a l was v a r i e d . The r a t s were r e l e a s e d from one of the f o u r p o l e s i n a pseudorandom sequence. Rats were always r e l e a s e d f a c i n g the w a l l of the p o o l . A t r i a l was over when the r a t mounted the p l a t f o r m or a f t e r 90 seconds had e l a p s e d , whichever came f i r s t . I f the r a t mounted the p l a t f o r m , i t was allowed t o remain on i t f o r 10 seconds. The l a t e n c y t o f i n d the p l a t f o r m was recorded. An e r r o r was r e c o r d e d i f the r a t c o n t a c t e d or attempted t o mount the n e g a t i v e cue o r i f the r a t c i r c l e d the n e g a t i v e cue as i f s e a r c h i n g f o r the escape p l a t f o r m . F o l l o w i n g the completion of t r a i n i n g , an a d d i t i o n a l e i g h t t r a n s f e r t r i a l were run on Day 11. T r a n s f e r t e s t s were run t o see what the r a t l e a r n e d d u r i n g t r a i n i n g and how i t would r e a c t when c o n f r o n t e d w i t h c o n d i t i o n s d i f f e r e n t from those t h a t e x i s t e d i n t r a i n i n g . The t r a n s f e r day a l s o c o n s i s t e d of 8 t r i a l s , summarized i n Table 3. In the f i r s t two t r i a l s o n l y the 35 Day 11-Transfer T r i a l s T r i a l 1 No n e g a t i v e cue. P l a t f o r m cued o n l y by the presence o f the p o s i t i v e cue 1. T r i a l 2 Same as T r i a l 1 u s i n g p o s i t i v e cue 2. T r i a l 3 Normal t r i a l t o s e t up f o r next t r i a l . Both the p o s i t i v e and n e g a t i v e cues ( p a i r 2) pr e s e n t . T r i a l 4 No p o s i t i v e cue. P l a t f o r m cued o n l y by the ( d i s t a l ) presence of the neg a t i v e cue 2. T r i a l 5 O r i g i n a l p a i r s mixed. P o s i t i v e cue from P a i r 1, ne g a t i v e cue from P a i r 2. T r i a l 6 Same as T r i a l 5, u s i n g the remaining two cues, p o s i t i v e cue 2 and ne g a t i v e cue 1. T r i a l 7 O r i g i n a l p a i r i n g o f p a i r 2. L o c a t i o n of cues and p l a t f o r m n ovel t o those used i n t r a i n i n g . T r i a l 8 Same procedure as T r i a l 8, u s i n g two a d d i t i o n a l novel l o c a t i o n s . T able 3. D e s c r i p t i o n o f t r i a l s on Day 11 of the Water-Based Concurrent D i s c r i m i n a t i o n Task. 36 p o s i t i v e was p r e s e n t . Negative cues were not p r e s e n t . T r i a l 3 and 4 t e s t e d the e f f e c t s of removing the p o s i t i v e cue. The l o c a t i o n of the p l a t f o r m was "cued" o n l y by the l o c a t i o n of the negative cue. In t r i a l s 5 and 6 the p a i r s were rearranged. The p o s i t i v e cue from the f i r s t p a i r was coupled w i t h the n e g a t i v e cue from the second, and the n e g a t i v e cue from p a i r one was p a i r e d w i t h the p o s i t i v e cue from p a i r two. The remaining t r i a l s t e s t e d the e f f e c t s o f changing the l o c a t i o n of the cues and p l a t f o r m t o novel p o s i t i o n s i n the p o o l . H i s t o l o g y and Anatomy F o l l o w i n g the completion of b e h a v i o r a l t e s t i n g animals i n the complex-reared, complex-cauterized, d a r k - r e a r e d , and dark-r e a r e d c a u t e r i z e d c o n t r o l groups were a n e s t h e t i z e d with sodium p e n t o b a r b i t a l and p e r f u s e d i n t e r c a r d i a l l y with 0.9% s a l i n e . The b r a i n s were removed and immersed whole i n 50 ml of Golgi-Cox s o l u t i o n ( G l a s e r & Van Der Loos, 1981). The s o l u t i o n was changed a f t e r two days and the b r a i n s were l e f t i n the dark f o r an a d d i t i o n a l 14-16 days. The b r a i n s were then p l a c e d i n a 30% s o l u t i o n o f sucrose f o r t h r e e t o f i v e days. The b r a i n s were then c u t i n t o 100 um s e c t i o n s w i t h a vibratome and mounted onto 2% g e l a t i n e - c o a t e d s l i d e s . B r a i n s were n u m e r i c a l l y coded so neurons c o u l d be drawn " b l i n d " . Neurons were drawn u s i n g a W i l d - L e i t z Combistereo Scope, w i t h a drawing tube attachment. D e n d r i t e s were c l e a r l y d e f i n e d i n the c o r t e x . Ten pyramidal c e l l s , f i v e on each s i d e , were drawn from l a y e r V c e l l s o f somatosensory (Par 1), v i s u a l 37 F i g u r e 5. A) Example of l a y e r V Pyramidal c e l l s drawn from somatosensory (Area P a r i ) , v i s u a l (Area 0c2M), and a u d i t o r y (Area T e l ) c o r t e x . B) I l l u s t r a t i o n of the c e n t r i f u g a l o r d e r i n g system? the r o o t segment i s the order 0 segment. 39 (Oc2M), and a u d i t o r y (Te 1) c o r t e x ( F i g u r e 5A). Layer V was s e l e c t e d because r e a r i n g c o n d i t i o n has been shown t o a f f e c t d e n d r i t i c branching of l a y e r V pyramidal c e l l s i n temporal and p a r i e t a l c o r t e x (Greenough, Volkmar, & Juraska, 1973). The d e n d r i t i c branching p a t t e r n was q u a n t i f i e d u s i n g the c e n t r i f u g a l o r d e r i n g system ( U y l i n g s , Van P e l t , Verwer, & McConnel, 1989). C e n t r i f u g a l o r d e r i n g i n d i c a t e s the t o p o l o g i c a l d i s t a n c e from the r o o t . I t s t a r t s w i t h numbering o r d e r from the d e n d r i t i c o r i g i n and i n c r e a s e s the order by one beyond each b i f u r c a t i o n ( F i g u r e 5B). Higher order branching was c o n s i d e r e d t o be a l l branching beyond order 6. Branching was summarized a c r o s s h i g h e r o r d e r s . Because a p i c a l d e n d r i t e s p r o j e c t through d i f f e r e n t l a y e r s w h i l e b a s i l a r d e n d r i t e s p r o j e c t w i t h i n the same l a y e r as the c e l l body, a p i c a l and b a s i l a r d e n d r i t e s were q u a n t i f i e d and analyzed s e p a r a t e l y . The animals i n the remaining ( l e s i o n e d ) experimental groups were a l s o a n e s t h e t i z e d w i t h sodium p e n t o b a r b i t a l and p e r f u s e d i n t e r c a r d i a l l y w i t h 0.9% p h y s i o l o g i c a l s a l i n e f o l l o w e d by 10% formal s a l i n e . B r a i n s were bloc k e d around the l e s i o n and s l i c e d through the l e s i o n e d area a t 40 um s e c t i o n s . S e c t i o n s were mounted on 1% g e l a t i n - c o a t e d s l i d e s . To v e r i f y the e x t e n t and l o c a t i o n of the l e s i o n s , s l i d e s were analyzed and l e s i o n s r e c o n s t r u c t e d under a microscope. 40 R e s u l t s B e h a v i o r a l Data To reduce the p r o b a b i l i t y of Type I e r r o r , the b e h a v i o r a l data were i n i t i a l l y assessed w i t h a m u l t i v a r i a t e a n a l y s i s of v a r i a n c e (MANOVA). A repeated measures Rearing C o n d i t i o n x L e s i o n Group MANOVA was conducted on the data generated i n a l l f i v e b e h a v i o r a l t a s k s (30 dependent v a r i a b l e s ) . Those animals f o r which t h e r e were incomplete data (15) were e l i m i n a t e d from the a n a l y s i s . To c r e a t e equal c e l l n's, data from an a d d i t i o n a l 9 animals were randomly e l i m i n a t e d (Glass & Hopkins, 1984). The t o t a l number of animals i n the a n a l y s i s was 60, 5 i n each group. O v e r a l l , the e f f e c t f o r R e a r i n g C o n d i t i o n was s i g n i f i c a n t , F(6,53) = 1.521, p < 0.05 (Wilks's lambda). However, no f u r t h e r s i g n i f i c a n t e f f e c t s were found f o r L e s i o n Group or Rearing x L e s i o n i n t e r a c t i o n . The s i g n i f i c a n t r e s u l t f o r Rearing C o n d i t i o n was f o l l o w e d up w i t h u n i v a r i a t e analyses of v a r i a n c e (ANOVA) f o r a l l dependent v a r i a b l e s . For the u n i v a r i a t e t e s t s , data were c o l l a p s e d a c r o s s a l l L e s i o n Groups w i t h i n each Rearing C o n d i t i o n . Short Test B a t t e r y 1) Grooming An a n a l y s i s of v a r i a n c e was used t o assess each of the t h r e e measures generated by the r a t s i n the f i v e minute grooming t e s t . The t h r e e measures were: (1) the t o t a l number of grooming sequences; (2) the t o t a l l a t e n c y spent grooming; (3) 41 the t o t a l number of grooming components. Although no s i g n i f i c a n t e f f e c t was found f o r the t o t a l number of grooming sequences over the f i v e minutes, the e f f e c t of Rearing C o n d i t i o n was s i g n i f i c a n t on both the t o t a l l a t e n c y spent grooming, F ( l , 5 9 ) = 3.397, p < 0.05, and the t o t a l number of grooming components, F ( l , 5 9 ) = 3.055, p < 0.05 ( F i g u r e 6 ). However, post-hoc comparisons (Tukey's HSD) d i d not f i n d s i g n i f i c a n t d i f f e r e n c e s between any p a i r i n g s of r e a r i n g c o n d i t i o n groups f o r e i t h e r v a r i a b l e . S i g n i f i c a n c e was found f o r both measures u s i n g a planned orthogonal c o n t r a s t which compared data pooled a c r o s s d a r k - r e a r e d and complex-reared groups: t o t a l l a t e n c y , F ( l , 5 6 ) = 10.13, p < 0.01; t o t a l number of components, F ( l , 5 6 ) = 8.862, p < 0.01. Thus, i t appears t h a t over the f i v e minute grooming t e s t , complex-reared (CR) r a t s groom l o n g e r , and demonstrate more grooming components than do d a r k - r e a r e d (DR) r a t s . 2) Dodaina and Wrenching C a u t e r i z a t i o n and/or d a r k - r e a r i n g (or s e l e c t i v e p o s t e r i o r c o r t i c a l l e s i o n s ) d i d not seem t o have any e f f e c t on the competence of a r a t t o p r o t e c t i t s food from o t h e r r a t s attempting t o s t e a l i t . The number of s u c c e s s f u l r o b b e r i e s a c r o s s a l l the dodging and wrenching t r i a l s t o t a l l e d l e s s than 10 out of a p o s s i b l e 600. D i d r a t s from d i f f e r e n t r e a r i n g c o n d i t i o n s make d i f f e r e n t types of responses i n a v o i d i n g food robbery attempts? The r a t i o of normal dodges t o a l l other p o s s i b l e responses was analyzed, and no s i g n i f i c a n t e f f e c t f o r R e a r i n g C o n d i t i o n was found. I t i s i n t e r e s t i n g t o note, 42 F i g u r e 6. A ) T o t a l d u r a t i o n of grooming i n seconds over the f i v e minute grooming t a s k f o r r a t s i n a l l f o u r r e a r i n g c o n d i t i o n s . B) T o t a l number of grooming components (body p a r t s ) groomed over the t o t a l d u r a t i o n of grooming. 43 A B CO •*-> c CD c o Q. E o O CD E 3 DR DRC CR CRC Rearing Condition DR DRC CR CRC Rearing Condition 4 4 however, t h a t the o v e r a l l i n c i d e n c e of dodging responses observed here d i f f e r e d from t h a t r e p o r t e d i n the study by Whishaw (1988). In the o r i g i n a l study by Whishaw, r a t s responded t o the robber s i t u a t i o n by a normal dodge more than 90% of the time. In t h i s study, r a t s responded w i t h a normal dodge o n l y 66% o f the time. 3) V j s y a l and TadtUe Novelty Discrimination A f t e r a t h r e e minute exposure t o p a i r s of i d e n t i c a l o b j e c t s , r a t s were s i m u l t a n e o u s l y presented w i t h a f a m i l i a r and a n o v e l o b j e c t and g i v e n t h r e e minutes t o e x p l o r e the p a i r . A u n i v a r i a t e a n a l y s i s of v a r i a n c e was conducted on the r a t i o of t o t a l time spent e x p l o r i n g the n o v e l o b j e c t t o t o t a l time spent e x p l o r i n g the f a m i l i a r o b j e c t . O v e r a l l , r a t s spent n e a r l y twice as long e x p l o r i n g the novel o b j e c t i n both the v i s u a l (mean = 1.86) and the t a c t i l e (mean - 1.71) c o n d i t i o n s . However, the impact of R e a r i n g C o n d i t i o n was not s i g n i f i c a n t f o r e i t h e r c o n d i t i o n . T h i s i n d i c a t e s t h a t the a b i l i t y t o d i s c r i m i n a t e between novel and f a m i l i a r o b j e c t s used i n the t a c t i l e and v i s u a l c o n d i t i o n s of t h i s t a s k i s not a f f e c t e d by c a u t e r i z a t i o n and/or dark r e a r i n g . Although t h e r e was not a s i g n i f i c a n t o v e r a l l L e s i o n Group e f f e c t i n the MANOVA, a l l u n i v a r i a t e ANOVAS f o r type of l e s i o n were run. One of the few s i g n i f i c a n t r e s u l t s r e v e a l e d , was on the t a c t i l e d i s c r i m i n a t i o n t a s k , F(2,48) = 4.356, p < 0.05 ( F i g u r e 7 ) . Post-hoc comparisons (Tukey's HSD) r e v e a l e d t h a t r a t s w i t h P a r i (somatosensory) l e s i o n s spent l e s s time e x p l o r i n g 45 F i g u r e 7. R a t i o of t o t a l time spent e x p l o r i n g the novel o b j e c t over t o t a l time spent e x p l o r i n g the f a m i l i a r o b j e c t d i s p l a y e d by r a t s i n the t h r e e s u r g i c a l c o n d i t i o n s on the T a c t i l e Novelty D i s c r i m i n a t i o n Task. 4 -r 3.8 -3.6 -3.4 -3.2 -3.0 -Control Pan Oc2M Lesion Group 46 the novel o b j e c t than d i d e i t h e r 0c2M ( v i s u a l ) l e s i o n e d o r c o n t r o l animals, p < 0.05. I t should again be noted t h a t because the o v e r a l l t e s t f o r r e a r i n g c o n d i t i o n was not s i g n i f i c a n t , t h i s r e s u l t f o r t a c t i l e d i s c r i m i n a t i o n , although i n t e r e s t i n g and p r e d i c t e d , i s somewhat suspect, and c o u l d be the r e s u l t of chance alone. Water-Based S p a t i a l Memory Task The l a t e n c y of r a t s from the f o u r r e a r i n g c o n d i t i o n s t o f i n d t h e submerged p l a t f o r m was compared on the f o u r t h , e i g h t h , t w e l f t h , and s i x t e e n t h t r i a l s . As c o n d i t i o n s were i d e n t i c a l f o r t r i a l s 1-4, 5-8, e t c . , o n l y the l a s t t r i a l i n each b l o c k of f o u r t r i a l s was assessed ( F i g u r e 8A). A s i g n i f i c a n t e f f e c t f o r Re a r i n g C o n d i t i o n was found f o r T r i a l Four, F(3,48) = 3.173, p < 0.05 ( F i g u r e 8B). Post-hoc comparisons (Tukey's HSD) d i d not r e v e a l any s i g n i f i c a n t d i f f e r e n c e s between r a t s r a i s e d i n the f o u r r e a r i n g c o n d i t i o n s . However, o v e r a l l the two dar k - r e a r e d groups were s i g n i f i c a n t l y d i f f e r e n t from the two complex-reared groups, F ( l , 5 6 ) = 8.588, p < 0.01 (Planned Orthogonal C o n t r a s t ) . I t appears t h a t CR r a t s showed f a s t e r escape l a t e n c i e s on t r i a l f o u r than d i d DR animals i n d i c a t i n g t h a t perhaps the CR r a t s had l e a r n e d the i n i t i a l t e s t c o n d i t i o n more thoroughly than d i d DR r a t s . No o t h e r s i g n i f i c a n t d i f f e r e n c e s were found on the remaining t r i a l s . On these t r i a l s DR r a t s d i d not appear t o be more d i s r u p t e d by the changing experimental c o n d i t i o n s than were CR animals. Although DR r a t s d i d not l e a r n the i n i t i a l t e s t c o n d i t i o n as q u i c k l y as d i d CR r a t s , t h e i r l e a r n i n g o f the 47 F i g u r e 8. A) Latency i n seconds t o fimd the submerged p l a t f o r m a c r o s s t r i a l s 4, 8, 12, and 16 f o r animals i n a l l f o u r r e a r i n g c o n d i t i o n s . B) Latency and standard d e v i a t i o n t o f i n d the p l a t f o r m on t r i a l 4 f o r r a t s i n the f o u r r e a r i n g c o n d i t i o n s . 48 A B 70 65 _ 60 CD 55 52 50 >, 45 40 35 30 o cz CD CO £ 25 CO o CO U J 20 15 10 5 0 trial 4 trial 8 trial 12 trial 16 Trial DR DRC CR C R C Rearing Condition 49 subsequent experimental c o n d i t i o n s was not impaired. Water-Based Concurrent V i s u a l D i s c r i m i n a t i o n Over t e n days of t r a i n i n g , r a t s had t o l e a r n t o d i s c r i m i n a t e between p a i r s o f v i s u a l cues t o l o c a t e the submerged p l a t f o r m . F o l l o w i n g the completion of ten t r a i n i n g days, r a t s were run (Day 11) on e i g h t d i f f e r e n t t r a n s f e r t r i a l s i n which they were c o n f r o n t e d w i t h s t i m u l u s c o n d i t i o n s d i f f e r e n t from those t h a t e x i s t e d d u r i n g t r a i n i n g . U n i v a r i a t e a n a l yses were run f o r : (1) escape l a t e n c y on t r a i n i n g days 1, 5, and 10; (2) t o t a l e r r o r s on t r a i n i n g days 1, 5, and 10; (3) escaped l a t e n c y f o r a l l e i g h t t r a n s f e r t r i a l s ; (4) t o t a l e r r o r s f o r t r a n s f e r t r i a l s 3 through 8. S i n c e no e r r o r s were committed by any r a t on t r a n s f e r t r i a l s 1 and 2, these c o n d i t i o n s were e l i m i n a t e d from the o r i g i n a l MANOVA a n a l y s i s and a l l subsequent u n i v a r i a t e a n a l y s e s . The data f o r t r a i n i n g days r e p r e s e n t an average s c o r e o f the e i g h t t r i a l s run each day. For t r a n s f e r t r i a l s each data p o i n t r e p r e s e n t s a s i n g l e t r i a l . A s i g n i f i c a n t e f f e c t f o r r e a r i n g c o n d i t i o n was found on T r a i n i n g Day 1, F(3,48) - 2.79, p < 0.05, and on T r a i n i n g Day 5, F(3,48) = 7.661), p < 0.001 ( F i g u r e 9 ) . A planned comparison between both DR and both CR groups f o r Day 1 was s i g n i f i c a n t , F ( l , 5 6 ) = 7.998, p < 0.01, i n d i c a t i n g t h a t r a t s from DR groups took lo n g e r t o f i n d the hidden p l a t f o r m than d i d r a t s from CR groups. Post hoc a n a l y s i s (Tukey's HSD) d i d not r e v e a l s i g n i f i c a n t d i f f e r e n c e s between any p a i r of r e a r i n g c o n d i t i o n s f o r t h i s t r a i n i n g day. For T r a i n i n g Day 5 the post-hoc 50 F i g u r e 9. Mean l a t e n c y i n seconds t o f i n d the cued submerged p l a t f o r m on T r a i n i n g Days 1, 5, and 10 f o r r a t s i n f o u r r e a r i n g c o n d i t i o n s . Day1 Day5 Day10 Training Day 51 comparisons d i d f i n d s i g n i f i c a n t d i f f e r e n c e s between i n d i v i d u a l groups. A l l p a i r i n g s of CR and CRC groups w i t h DR and DRC groups were s i g n i f i c a n t (Tukey's HSD, a l l p's < 0.05). Again, a l l DR groups were l e s s e f f e c t i v e than CR groups. No s i g n i f i c a n t d i f f e r e n c e s i n escape l a t e n c i e s were found between Rearing C o n d i t i o n s on T r a i n i n g Day 10. I t appears t h a t , although the DR groups were slower t o a c q u i r e the t a s k , by the l a s t day of t r a i n i n g , t h e i r escape l a t e n c i e s d i d not d i f f e r s i g n i f i c a n t l y from those of CR groups. In a n a l y z i n g t h e number of e r r o r s committed on the same t r a i n i n g days, a s i g n i f i c a n t e f f e c t f o r Rearing C o n d i t i o n was o b t a i n e d o n l y f o r T r a i n i n g Day 10, F(3,48) = 3.505, p < 0.05 ( F i g u r e 10). Post-hoc comparisons (Tukey's HSD) found the CR animals t o make s i g n i f i c a n t l y more e r r o r s than the DR animals. T h i s r e s u l t i s e s p e c i a l l y i n t e r e s t i n g i n l i g h t of the n o n s i g n i f i c a n t r e s u l t f o r escape l a t e n c y on the same t r a i n i n g day. I t appears t h a t by Day 10, although t h e CR group i s as qui c k t o f i n d the p l a t f o r m as a l l o t h e r groups, they make s i g n i f i c a n t l y more e r r o r s than a t l e a s t the DR group i n the p r o c e s s . I t s h o u l d be noted t h a t although t h i s r e s u l t f o r number of e r r o r s was s i g n i f i c a n t , i t was the o n l y time t h a t any of the groups d i f f e r e d s i g n i f i c a n t l y on e r r o r s a c r o s s any of the t r a i n i n g o r t r a n s f e r t r i a l s . Post-hoc u n i v a r i a t e ANOVA's were conducted t o assess e r r o r s committed on T r a i n i n g Days 8 and 9, days not i n c l u d e d i n the o r i g i n a l a n a l y s i s . No s i g n i f i c a n t d i f f e r e n c e s between r e a r i n g c o n d i t i o n s were found, making the r e s u l t f o r Day 10 somewhat sus p e c t . 52 F i g u r e 10. Mean number of t o t a l e r r o r s committed i n f i n d i n g the submerged p l a t f o r m on T r a i n i n g Days 1, 5, and 10 f o r r a t s i n a l l r e a r i n g c o n d i t i o n s . CO o 4 UJ o l _ CD - O E 3 -2 -c a> 1 0 Z m Day1 1 m Day5 • DR •0 DR'C m CR O C R C 1 Day10 Training Day 53 A n a l y s i s of escape l a t e n c i e s a c r o s s the e i g h t t r a n s f e r t r i a l s r e v e a l e d s i g n i f i c a n t e f f e c t of Rearing C o n d i t i o n o n l y on t r a n s f e r t r i a l s where the o r i g i n a l cue p a i r s were mixed: T r i a l 5, F(3,48) = 5.187, p < 0.01; t r i a l 6, F(3,48) = 3.714, p < 0.05 ( F i g u r e 11). Post-hoc comparisons f o r T r i a l 5 found DRC animals to be s i g n i f i c a n t l y slower than both CR and CRC groups. On T r i a l 6, the DR group took s i g n i f i c a n t l y l onger t o f i n d the p l a t f o r m than the CR group (Tukey's HSD, a l l p's < 0.05. No oth e r s i g n i f i c a n t e f f e c t s f o r escape l a t e n c y were found on any of the other t r a n s f e r t r i a l c o n d i t i o n s , such as on T r i a l s 7 and 8 where the l o c a t i o n s o f the cues and p l a t f o r m were n o v e l t o those used i n t r a i n i n g . From these r e s u l t s i t appears t h a t mixing the cue p a i r s d i s r u p t e d the performance of the DR groups more than CR groups, but o n l y i n terms of escape l a t e n c y . U n i v a r i a t e a n a l y s i s of v a r i a n c e f o r e r r o r s committed on t r a n s f e r t r i a l s t h r e e through e i g h t were a l l n o n s i g n i f i c a n t . Escape l a t e n c y proved t o be a more s e n s i t i v e assay of e a r l y r e a r i n g c o n d i t i o n s than e r r o r s . Histological and Anatomica1: V e r i f i c a t i o n of L e s i o n L o c a t i o n B r a i n s were b l o c k e d and s e c t i o n e d a t 40 microns through the ex t e n t of the c o r t i c a l l e s i o n . Mounted s e c t i o n s were analyzed v i s u a l l y t o v e r i f y the ex t e n t of the l e s i o n . R e c o n s t r u c t i o n s of r e p r e s e n t a t i v e a b l a t i o n s are shown i n F i g u r e 12. G e n e r a l l y the l e s i o n s were w e l l p l a c e d . However, some v a r i a t i o n of l e s i o n 54 F i g u r e 11. Mean escape l a t e n c y i n seconds t o f i n d the cued p l a t f o r m on T r a n s f e r T r i a l s 5 and 6, f o r r a t s i n a l l r e a r i n g c o n d i t i o n s . These t r i a l s r e p r e s e n t s i t u a t i o n where the o r i g i n a l cue p a i r s from the t r a i n i n g p o r t i o n of the Water-Based Concurrent D i s c r i m i n a t i o n Task are mixed. TrlalS Trlal6 Trial Q 55 F i g u r e 12. R e c o n s t r u c t i o n of A) P a r i , primary somatosensory c o r t e x c o n t a i n i n g the v i b r i s s a e b a r r e l f i e l d s , and B) 0c2M, e x t r a s t r i a t e v i s u a l c o r t e x l e s i o n s . 57 58 s i z e was observed i n both P a r i (somatosensory) and 0c2M ( v i s u a l ) l e s i o n s . M i c r o s c o p i c e v a l u a t i o n s of the s e c t i o n e d b r a i n s r e v e a l e d t h a t o n l y a few of the i n j u r i e s produced d i r e c t damage to s t r u c t u r e s below the l e v e l of the corpus collosum. As w e l l , approximately one t h i r d of the l e s i o n s d i d not completely remove a l l of the intended c o r t i c a l a r e a. To determine i f v a r i a t i o n i n s i z e of l e s i o n was c o r r e l a t e d w i t h behavior, b e h a v i o r a l data f o r l e s i o n e d animals were r e a n a l y z e d . A r e p e a t e d measures MANOVA compared the b e h a v i o r a l outcomes of r a t s c l a s s i f i e d as having " l a r g e " , "complete", or " s m a l l " l e s i o n s w i t h i n each L e s i o n Group. The a n a l y ses d i d not r e v e a l a s i g n i f i c a n t r e l a t i o n s h i p between l e s i o n s i z e and b e h a v i o r i n the case of e i t h e r P a r i o r 0c2M l e s i o n e d animals. In g e n e r a l , l e s i o n s i z e was not seen t o a f f e c t performance i n any c o n s i s t e n t way. The b e h a v i o r a l measures taken of r a t s with l a r g e or s m a l l l e s i o n s were not found t o be q u a n t i t a t i v e l y d i f f e r e n t from those of more a c c u r a t e l y l e s i o n e d animals. T h e r e f o r e , l e s i o n s i z e probably does not account f o r a s i g n i f i c a n t amount of the b e h a v i o r a l v a r i a n c e found i n t h i s study. impact o f R e a ring C o n d i t i o n on D e n d r i t i c A r b o r i z a t i o n The e f f e c t of d i f f e r e n t r e a r i n g c o n d i t i o n s on d e n d r i t i c a r b o r i z a t i o n was assessed s e p a r a t e l y f o r a p i c a l and b a s a l e r d e n d r i t e s . Data were ob t a i n e d from f i v e r a t s i n each r e a r i n g c o n d i t i o n f o r a t o t a l of 20 r a t s . The animals i n c l u d e d i n the anatomical assessment d i d were the l e s i o n c o n t r o l animals. 59 These were the same as animals as those t h a t d i d not r e c e i v e c o r t i c a l s u r g i c a l i n t e r v e n t i o n i n the b e h a v i o r a l a n a l y s i s . i ) A p i c a l Dendrites To assess e x t e n t of d e n d r i t i c a r b o r i z a t i o n i n t h r e e sensory c o r t i c a l areas a one f a c t o r (Rearing C o n d i t i o n ) repeated measures MANOVA was conducted ( t o t a l of 6 o r d e r s of branching x 3 areas = 18 dependant v a r i a b l e s ) . The a n a l y s i s r e v e a l e d a s i g n i f i c a n t e f f e c t of r e a r i n g c o n d i t i o n on o v e r a l l e x t e n t of a r b o r i z a t i o n , F(3,16) = 11.889, p < 0.001. T h i s r e s u l t was f o l l o w e d up by a repeated measures ANOVA f o r each a r e a . In area P a r i , somatosensory c o r t e x , s i g n i f i c a n t e f f e c t s were found f o r r e a r i n g c o n d i t i o n , F(3,16) = 5.365, p < 0.01, and f o r the i n t e r a c t i o n of r e a r i n g c o n d i t i o n x order of branching, F(5,80) = 4.212, p < 0.001 ( F i g u r e 13A). Post-hoc a n a l y s i s of these data i n d i c a t e d t h a t the CRC group showed s i g n i f i c a n t l y more o v e r a l l a p i c a l a r b o r i z a t i o n averaged a c r o s s a l l o r d e r s of b r a n c h i n g i n Area P a r i than the DR and the DRC group. As w e l l , both CR groups showed s i g n i f i c a n t l y more h i g h o r d e r (order 6) branching than both of the DR groups (Tukey's HSD, a l l p's < 0.05) ( F i g u r e 13B). The a n a l y s i s f o r area Oc2M, v i s u a l c o r t e x , d i d not r e v e a l a main e f f e c t f o r r e a r i n g c o n d i t i o n . However, a s i g n i f i c a n t i n t e r a c t i o n between r e a r i n g c o n d i t i o n and order of branching was found, F(5,80) = 2.037, p < 0.05 ( F i g u r e 14A). Post-hoc comparisons (Tukey's HSD) found the CRC group t o have s i g n i f i c a n t l y more h i g h e r order branching t h a t any o t h e r group, 6 0 F i g u r e 13. A) Mean of mean number of d e n d r i t i c branches f o r r a t s i n a l l r e a r i n g c o n d i t i o n s i n area P a r i . B) Mean of mean number of h i g h e r order branching f o r a l l r e a r i n g c o n d i t i o n s i n area P a r i . 00 Mean Number of Branches > Mean Number of Branches 62 F i g u r e 14. A) Mean of mean number of d e n d r i t i c branches found i n secondary v i s u a l c o r t e x , area 0c2M, f o r r a t s i n a l l r e a r i n g c o n d i t i o n s . B) Summary of mean of mean number of h i g h e r order d e n d r i t i c branches f o r r a t s i n a l l r e a r i n g c o n d i t i o n s i n area 0c2M. DO Mean Number of Branches Mean Number of Branches 64 F i g u r e 15. A) Mean of mean number of d e n d r i t i c branching found i n primary a u d i t o r y c o r t e x , area T e l , a sensory system not d i r e c t l y manipulated, f o r r a t s i n a l l r e a r i n g c o n d i t i o n s . B) Summary of mean of mean number of h i g h e r order d e n d r i t i c branches f o r r a t s i n a l l r e a r i n g c o n d i t i o n s i n area T e l . DO Mean Number of Branches > Mean Number of Branches 66 p < 0.05 ( F i g u r e 14B). A s i g n i f i c a n t e f f e c t f o r r e a r i n g c o n d i t i o n was found i n area T e l , a u d i t o r y c o r t e x , F(3,16) = 8.115, p < 0.01. The CRC group showed s i g n i f i c a n t l y more a r b o r i z a t i o n a c r o s s a l l o r d e r s of branching i n primary a u d i t o r y c o r t e x than any o t h e r group (Tukey's, p < 0.05). As shown i n F i g u r e 15A the a n a l y s i s again r e v e a l e d a s i g n i f i c a n t r e a r i n g c o n d i t i o n x o r d e r of branching i n t e r a c t i o n , F(5,80) = 7.532, p < 0.001. Post-hoc comparisons found s i g n i f i c a n t l y more h i g h e r o r d e r branching i n the CRC group than any o t h e r group (Tukey's, p < 0.05) ( F i g u r e 15B). D e n d r i t i c a r b o r i z a t i o n i n a l l t h r e e c o r t i c a l areas was s i g n i f i c a n t l y g r e a t e r i n the two CR groups than i n the two DR groups: Area P a r i , F ( l , 1 6 ) = 15.417, p < 0.01; Area Oc2M, F ( l , 1 6 ) = 4.522, p < 0,05; Area T e l , F ( l , 1 6 ) = 11.829, p < 0.01 (Planned Orthogonal C o n t r a s t ) . There were no s i g n i f i c a n t d i f f e r e n c e s i n any c o r t i c a l area when c a u t e r i z e d and i n t a c t groups were compared. 2) Basilar Dendrites A one f a c t o r repeated measures MANOVA, the same as was used f o r a p i c a l d e n d r i t e s , was conducted t o assess a r b o r i z a t i o n of b a s i l a r d e n d r i t e s . No s i g n i f i c a n t main o r i n t e r a c t i o n e f f e c t s were found. 67 D i s c u s s i o n Impact of E a r l y s i m u l a t i o n H i s t o r y on Behavior In s t u d y i n g the r e l a t i o n s h i p between b r a i n and behavior one approach i s t o a l t e r the environment i n which the b r a i n normally develops and then c h a r t how n e u r a l and b e h a v i o r a l outcomes change. The f o u r r e a r i n g c o n d i t i o n s i n c l u d e d i n t h i s study combined enhancement and d e p r i v a t i o n of the somatosensory and/or v i s u a l systems. One of the purposes f o r u n d e r t a k i n g t h i s study was t o determine the i n t r a - and intermodal impact of the d i f f e r e n t i a l r e a r i n g c o n d i t i o n s on b e h a v i o r . The o v e r a l l e f f e c t f o r R e a r ing C o n d i t i o n was s i g n i f i c a n t , i n d i c a t i n g t h a t e a r l y m a n i p u l a t i o n of the somatosensory and v i s u a l systems d i d have an impact on performance of b e h a v i o r a l t a s k s . F u r t h e r a n a l y s i s of the i n d i v i d u a l t a s k s assessed the intramodal e f f e c t s of e a r l y sensory r e s t r i c t i o n as w e l l as served as a d i r e c t t e s t of the modality-interdependence model proposed by Turkewitz and Kenny (1982). The two main hypothesis a r i s i n g from t h i s model ar e : 1) e a r l y r e s t r i c t i o n of sensory i n p u t i n one m o d a l i t y c o u l d r e s u l t i n intermodal compensation due t o l a c k of c o m p e t i t i o n from t h i s r e s t r i c t e d m o d a lity; 2) e a r l y r e s t r i c t i o n of sensory i n p u t i n t o an e a r l y d e v e l o p i n g m o d a l i t y might d i s r u p t the emerging o r g a n i z a t i o n a l framework necessary f o r a competency which i n v o l v e s s i g n a l s of a l a t e r d e v e l o p i n g m o d a l i t y . L i t t l e support f o r e i t h e r h y p o t h e s i s was found i n the p r e s e n t b e h a v i o r a l a n a l y s i s . 68 V i s u a l d e p r i v a t i o n through r e a r i n g i n t o t a l darkness has p r e v i o u s l y been shown t o slow a c q u i s i t i o n of v a r i o u s non v i s u a l -s p a t i a l t a s k s (Tees, Midgley, & N e s b i t , 1981). As expected, a d i f f e r e n c e between dark and complex r e a r e d r a t s i n escape l a t e n c y t o l o c a t e the hidden p l a t f o r m was found. S u r p r i s i n g l y , t h i s d i f f e r e n c e was p r e s e n t o n l y on t r i a l f o u r . Dark r e a r e d r a t s appeared t o have more d i f f i c u l t y than complex r e a r e d r a t s o n l y i n l e a r n i n g the i n i t i a l r e l a t i o n s h i p between the proximal and d i s t a l cues and the p l a t f o r m . F o l l o w i n g t h i s phase, however, the r e l a t i o n s h i p between cues was changed an a d d i t i o n a l t h r e e times. On subsequent t r i a l s , dark r e a r e d r a t s were not s i g n i f i c a n t l y worse a t adapting t o these changes and l e a r n i n g the new r u l e s f o r l o c a t i n g the p l a t f o r m than were complex r e a r e d r a t s . The impact of dark r e a r i n g on the v i s u a l - s p a t i a l a b i l i t i e s and v i s u a l l y guided behavior i n t h i s study seems, at b e s t , t o be l i m i t e d . I f r e s t r i c t i o n of sensory i n p u t t o an e a r l y d e v e l o p i n g m o d a l i t y d i s r u p t s the o r g a n i z a t i o n a l framework necessary f o r a s p a t i a l competency i n v o l v i n g s i g n a l s i n a l a t e r d e v e l o p i n g m o d a l i t y , then the c a u t e r i z e d animals would be expected t o be l e s s c apable. E a r l y t a c t i l e r e s t r i c t i o n through c a u t e r i z a t i o n of v i b r i s s a e had no e f f e c t on v i s u a l - s p a t i a l b e h a v i o r as assessed by the p r e s e n t v e r s i o n of the water maze t a s k . Even when e a r l y dewhiskered animals were a l s o d a r k - r e a r e d , performance was not a f f e c t e d . However, e x p e c t i n g e a r l y somatosensory r e s t r i c t i o n t o a f f e c t s p a t i a l b e h a v i o r assumes developmental dependence between these c a p a c i t i e s . I t may be 69 t h a t t a c t i l e i n p u t i s unnecessary f o r the development of normal v i s u a l - s p a t i a l b e havior. I f the o r g a n i z a t i o n and development of s p a t i a l behavior i s p r i m a r i l y dependent on the a p p r o p r i a t e v i s u a l i n p u t , then t a c t i l e r e s t r i c t i o n would be of no consequence t o s p a t i a l b e h a v i o r s . I t has been suggested i n the l i t e r a t u r e t h a t v i s u a l i n p u t i s of primary importance f o r d e v e l o p i n g a p p r o p r i a t e s p a t i a l b ehavior ( B u r n s t i n e e t a l , 1984, Tees e t a l , 1981). The Water-based Concurrent D i s c r i m i n a t i o n Task produced s i m i l a r r e s u l t s t o those found w i t h the S p a t i a l L e a r n i n g Task. Long term dewhiskering through c a u t e r i z a t i o n d i d not q u a l i t a t i v e l y a f f e c t the a b i l i t y t o v i s u a l l y r e c o g n i z e and remember which o b j e c t w i t h i n the two p a i r s of v i s u a l s t i m u l i was a s s o c i a t e d w i t h the hidden p l a t f o r m . When c a u t e r i z e d r a t s were compared t o i n t a c t groups i n the same v i s u a l c o n d i t i o n ( i e . DR c a u t e r i z e d v s . DR, CR c a u t e r i z e d v s . CR), c a u t e r i z e d groups d i d not take l o n g e r t o reach the p l a t f o r m , nor d i d they commit more e r r o r s i n the p r o c e s s , than d i d i n t a c t r a t s . T h i s was t r u e f o r both t r a i n i n g and t r a n s f e r t r i a l s . Again, as f a r as s t i m u l i are concerned, t h i s i s an almost p u r e l y v i s u a l l y based t a s k . These r e s u l t s might i n d i c a t e t h a t t a c t i l e i n p u t i s not necessary f o r the development o f the a b i l i t y t o r e s o l v e v i s u a l d e t a i l , d i s c r i m i n a t e between d i f f e r e n t p a t t e r n s , and remember d i f f e r e n c e s between p a t t e r n s . Furthermore, because t a c t i l e cues are not necessary t o s o l v e the problem f a c i n g the r a t s , t a c t i l e r e s t r i c t i o n was of no consequence t o a d u l t performance. 70 As expected, dark-rearing d i d seem to have an e f f e c t on performance on t h i s task. Although dark-rearing has not been shown to a f f e c t the a b i l i t y of rats to resolve d e t a i l per se (Friedman & Green, 1982), they do take longer to acquire various kinds of pattern discriminations (Tees, 1979). This delayed a c q u i s i t i o n i s r e f l e c t e d i n the analysis of latency on t r a i n i n g days 1, 5, and 10. CR rats are able to discriminate and remember the two pairs by day 5, while the same l e v e l s of performance are not achieved by DR groups u n t i l day 10. The poor performance of DR rats may r e f l e c t a problem i n the a b i l i t y to concurrently learn and remember two p o s i t i v e s t i m u l i , not d i f f i c u l t y with resolving differences between s t i m u l i . The r e s u l t s of the analysis of transfer t r i a l s indicated that DR rats were more disrupted by mixing the o r i g i n a l cue pairs than were CR r a t s . This too i s consistent with the r e s u l t s of DR rats taking longer to acquire pattern discriminations (Tees, 1979). Although the rule didn't change for these t r i a l s , that i s p o s i t i v e cues from previous t r i a l s remained as p o s i t i v e cues, the pairings did change, r e s u l t i n g i n a novel pattern discrimination facing the r a t . One factor that may have influenced the r e s u l t s i s that t h i s task was run following the completion of the s p a t i a l learning task. Having had previous experience with a water maze task, rats had already learned that there was a submerged platform i n the pool. Although i t i s u n l i k e l y that t h i s had s i g n i f i c a n t impact on the f i n a l outcome (Kolb & Walkey, 1987), i t i s possible d i f f e r e n t strategies to locate the platform may 71 have been employed i n the i n i t i a l a c q u i s i t i o n phase. Naive animals may have taken longer t o l e a r n t h i s t a s k had they not have had p r e v i o u s experience w i t h the water maze s i t u a t i o n . A l t e r n a t i v e l y , having t o s w i t c h from a p l a c e l e a r n i n g t a s k t o a v i s u a l d i s c r i m i n a t i o n t a s k w h i l e i n the same t e s t i n g environment, c o u l d w e l l have been expected t o be more d i s r u p t i v e t o s p e c i f i c animals w i t h d i f f e r e n t e a r l y r e s t r i c t i v e s t i m u l a t i o n h i s t o r i e s . The remaining t h r e e t a s k s were t e s t s of s p e c i e s s p e c i f i c b e h a v i o r s . The r e s u l t s of the grooming t a s k proved t o be somewhat s u r p r i z i n g . O v e r a l l , CR r a t s groomed more body components and f o r l o n g e r p e r i o d than d i d DR animals. DR and CR d i d not, however, d i f f e r i n the number o f grooming segments they i n i t i a t e d . There i s some evidence t o suggest t h a t f o l l o w i n g e a r l y c o r t i c a l l e s i o n s , s p a r i n g o f f u n c t i o n i s more common on l e a r n i n g t a s k s than of t e s t s of s p e c i e s t y p i c a l b e h a v i o r s (Kolb & Whishaw, 1989). D a r k - r e a r i n g may have had a s i m i l a r e f f e c t on the n a t u r a l l y o c c u r r i n g b e h a v i o r of grooming. However, as the c o r t i c a l impact o f e a r l y dark o r complex-rearing i s thought t o be more d i f f u s e , (Tees, 1990), t h i s i s u n l i k e l y . Although the r a t s had spent an equal amount of time b e i n g handled and h a b i t u a t e d t o the chamber, i t i s p o s s i b l e t h a t the experience of b e i n g i n the chamber, even under the dim l i g h t i n g c o n d i t i o n s , was much more d i s t r a c t i n g f o r the DR r a t s than i t was f o r the CR r a t s , e s p e c i a l l y s i n c e t h i s was the f i r s t b e h a v i o r a l t a s k a l l animals were t e s t e d on. I t i s p o s s i b l y f o r t h i s reason t h a t , although equal number o f grooming sequences 72 were i n i t i a t e d f o r a l l groups, the DR r a t s d i d not c a r r y through as t h o r o u g h l y . Other experiments, however, show DR r a t s t o be as s u c c e s s f u l as o t h e r groups on i n i t i a l v i s u a l d i s c r i m i n a t i o n t a s k s (Tees, 1990). Dewhiskering and/or d a r k - r e a r i n g had no s i g n i f i c a n t impact on performance on the Dodging and Wrenching paradigm. The a b i l i t y of r a t s t o s u c c e s s f u l l y defend t h e i r food was u n a f f e c t e d by r e a r i n g c o n d i t i o n . The type of response e l i c i t e d by a v i c t i m when c h a l l e n g e d by a robber was a l s o c o n s i s t e n t a c r o s s a l l r e a r i n g c o n d i t i o n s , although d i f f e r e n t from the o r i g i n a l f i n d i n g s by Whishaw and Tomie (1987). As acute dewhiskering and b l i n d i n g have not been found t o have an impact on performance i n the Dodging and Wrenching t a s k (Buhrmann & Tees, unpublished) i t i s u n l i k e l y t h a t the r e s u l t s on t h i s t a s k can be e x p l a i n e d by intermodal compensation o c c u r r i n g d u r i n g development. I t may be more p l a u s a b l e t o conclude t h a t success on t h i s t a s k i s dependent on i n p u t s not a f f e c t e d by v i s u a l o r v i b r i s s a l sensory m a n i p u l a t i o n s . There was no s i g n i f i c a n t e f f e c t f o r r e a r i n g c o n d i t i o n i n e i t h e r the t a c t i l e o r v i s u a l c o n d i t i o n s of the n o v e l t y d i s c r i m i n a t i o n t a s k . In both c o n d i t i o n s r a t s d i d spend almost t w i c e as long e x p l o r i n g the n o v e l o b j e c t as they d i d the f a m i l i a r o b j e c t . For the t a c t i l e c o n d i t i o n , the presence of v i b r i s s a e d u r i n g development d i d not appear t o be important t o the a b i l i t y t o r e c o g n i z e and remember the t e x t u r a l d i s c r i m i n a t i o n u t i l i z e d i n these c a s e s . S i n c e c a u t e r i z a t i o n r e s t r i c t s sensory i n p u t o n l y from the r e c e p t o r s l o c a t e d i n the 73 v i b r i s s a e f o l l i c l e s intramodal compensation may have occurred. To discriminate between novel and f a m i l i a r t a c t i l e l y d i s t i n c t objects, cauterized subjects could be r e l y i n g on input from other somatosensory receptors. Results on the v i s u a l condition are i n accordance with the r e s u l t s of the water based v i s u a l discrimination task. DR rats were not impaired i n t h e i r a b i l i t y to resolve the differences between these shapes. Cauterization also had no e f f e c t on performance on t h i s task. Early t a c t i l e r e s t r i c t i o n does not appear to intermodally impact on the development of t h i s a b i l i t y e i t h e r . Perhaps, i f the t e s t s t i m u l i used f o r t h i s task had been more complex, differences between d i f f e r e n t rearing conditions may have been revealed. In a cubic volume discrimination task, enriched golden hamsters were able to make learning transfers to more d i v e r s i f i e d t e s t s i t u a t i o n s than were standard subjects (Thinus-Blanc, 1982). In comparing the behavioral outcomes of the four rearing conditions, pairwise post-hoc comparisons often d i d not reveal any s i g n i f i c a n t differences between any of the groups. S i g n i f i c a n t r e s u l t s f o r univariate ANOVA's were explained only by combining the data from the DR and DRC groups and comparing that to the combined data from the CR and CRC groups. There were never any s i g n i f i c a n t differences found between cauterized and i n t a c t groups reared within the same " v i s u a l " rearing (dark-reared or complex-reared) condition. The main rearing condition e f f e c t can be narrowed down to an e f f e c t for dark-rearing r e l a t i v e to complex-rearing. 74 The minimal behavioral e f f e c t s f o r cauterization could be used as support f o r the idea of intermodal compensation. As the somatosensory system i s the e a r l i e s t system to develop, early r e s t r i c t i o n could be compensated f o r by other l a t e r developing systems. If intermodal compensation had occurred, the behavioral impact of early cauterization would be minimal, as was observed. However, another p o s s i b i l i t y i s that intramodal, not intermodal, compensation has occurred. Cauterization as a method of early r e s t r i c t i o n of the somatosensory system may not be a s u f f i c i e n t manipulation. Although i n t a c t v i b r i s s a e are believed to be very important to the normal functioning of the rat , and that the end points of t h e i r c o r t i c a l projections (the c o r t i c a l b a r r e l f i e l d s ) account f o r a f u l l 30% of primary somatosensory cortex, 70% of primary somatosensory cortex i s s t i l l receiving input from a wide v a r i e t y of somatosensory receptors. Not even the r e s t r i c t i o n of input from the mystacial area i s complete. Projections from sensory receptors located i n the skin around the v i b r i s s a e are s t i l l inputting into the cortex (Kaas et a l , 1983). Before i t i s necessary to consider intermodal compensation as an explanation f o r the lack of d e f i c i t s demonstrated by the cauterized groups, the p o s s i b i l i t y of intramodal compensation occurring should be considered. Previous research has shown that following v i b r i s s a e loss behaviors f o r which v i b r i s s a e are considered important a l l to some degree survive v i b r i s s a e removal (Kerimidas, 1976). For example, rats w i l l learn to jump across a gap i n an elevated 75 platform to receive a food reward (Hutson & Masterton, 1986). V i b r i s s a l removal decreases the width of the gap a r a t would jump, presumably because without t h e i r v i b r i s s a e , they could not bridge (make contact with the other side) as large a gap. However, as long as the f a r side could be contacted with the snout (which contains many other somatosensory receptors besides the v i b r i s s a e receptors), the r a t would jump the gap. Thus, the rat has compensated (although not completely) for v i b r i s s a l loss by using input from other somatosenory receptors. Perhaps when looking at the impact of early somatosensory r e s t r i c t i o n on the development of other sensory systems, i t would be more e f f e c t i v e to use a more complete form of somatosensory r e s t r i c t i o n . Options such as cuttin g the common somatosensory pathway through the thalamus, or l a t e r common t r a c t s projecting to the cortex, should be explored a means of giving a more complete picture of the i n t e r - and intramodal e f f e c t of early somatosensory r e s t r i c t i o n . Selective Posterior C o r t i c a l Lesions A second approach to the study the r e l a t i o n s h i p between brain and behavior i s to "perturb" the a b i l i t i e s of the r a t by inducing s e l e c t i v e lesions, and observe how behavior changes. C o r t i c a l areas are f u n c t i o n a l l y d i s t i n c t d i v i s i o n s of the brain. Restricted lesions can produce very s p e c i f i c and i r r e v e r s i b l e changes i n behavior (Kaas, 1987). The l a t e r addition of s e l e c t lesions to Pari (somatosensory) and 0c2M (visual) cortex was to serve two purposes i n t h i s study. The f i r s t was an attempt to 7 6 gain further insight into the p l a s t i c i t y surrounding manipulations of early rearing environment. If there were an interactions between l e s i o n group and rearing condition, then a clearer picture of the i n t r a - and intermodal e f f e c t s of early somatosensory and v i s u a l deprivation would be attained. The second purpose for including the l e s i o n groups was an attempt to further delineate the functions that are l o c a l i z e d i n areas Pari and 0c2M. The analysis did not reveal a s i g n i f i c a n t e f f e c t f o r les i o n group. There was also no e f f e c t f o r the in t e r a c t i o n of les i o n type and rearing condition. In general, the behavioral a b i l i t i e s (as r e f l e c t e d i n performance on the tasks) of rats with eith e r v i s u a l or somatosensory c o r t i c a l lesions were not s i g n i f i c a n t l y d i f f e r e n t from those of t h e i r comparable control groups. Inconsistency of l e s i o n s i z e as revealed by h i s t o l o g i c a l examination may have eliminated l e s i o n e f f e c t s . To assess t h i s p o s s i b i l i t y , the behavioral performances of rats c l a s s i f i e d as having small, large, or accurate lesions were compared. The analyses were conducted separately for Pari and Oc2H le s i o n groups. There were no consistent e f f e c t s f o r ei t h e r l e s i o n . Although the performance of rats with d i f f e r e n t l e s i o n s i z e s did d i f f e r s i g n i f i c a n t l y from each other on two or three out of the 32 dependent measures considered, these e f f e c t s did not reveal a pattern. For instance, the rats with larger lesions were not always the worst o f f , nor were those with the smaller lesions the le a s t impaired. This was true f o r both area Pari (somatosensory) and area 0c2M (visual) cortex. For t h i s 77 reason, i t does not appear that the s i z e and/or accuracy of the lesions played a central r o l e i n the o v e r a l l outcome of t h i s study. A second p o s s i b i l i t y i s that the behavioral t e s t s were not se n s i t i v e to functions of the c o r t i c a l areas focused on i n t h i s study, and therefore, no behavioral d e f i c i t s were observed. Task s e l e c t i o n i s d i f f i c u l t when the behavioral impact of s e l e c t i v e lesions i s simply not well documented. For instance, as area 0c2M i s most commonly part of a large c o r t i c a l l e s i o n i n combination with other c o r t i c a l v i s u a l areas, the precise function of area 0c2M can only be speculated on (Dean, 1990). A f i n a l a l t e r n a t i v e i s that the e f f e c t for l e s i o n may not have been s i g n i f i c a n t simply because there were so many factors included i n the study (Glass & Hopkins, 1984). Subtle adverse e f f e c t s could e a s i l y have been l o s t because of nature of the analysis. Furthermore, the nature of the dependent measures was such that not a l l the measures were expected to r e s u l t i n the same d i r e c t i o n of an e f f e c t f o r each l e s i o n group across a l l rearing conditions. Some of the tasks were included i n the battery of behavioral t e s t s because i t was thought that they would s p e c i f i c a l l y be s e n s i t i v e to somatosensory cortex function, some were thought to be more v i s u a l l y based, while f o r others there was more of a p o s s i b i l i t y for an i n t e r a c t i o n between the factors of rearing and l e s i o n . With so many variables, so many experimental groups, and l i m i t e d numbers of subjects i n each group, the power to f i n d any differences between groups was severely diminished. Only the strongest and 78 most robust e f f e c t s or interactions would have survived such an analysis. One s i g n i f i c a n t r e s u l t worth mentioning i n sp i t e of the nonsignificant o v e r a l l l e s i o n e f f e c t i s the r e s u l t on the t a c t i l e condition of the novelty discrimination task. Rats with Pari (somatosensory) cortex lesions spent less time exploring the novel object than did both the v i s u a l l y lesioned and control groups. Although t h i s may be a chance finding, other researchers have found s i m i l a r r e s u l t s following somatosensory lesions. An e a r l i e r study by Finger (1978) found rats with b i l a t e r a l lesions of the somatosensory cortex to be less able to make te x t u r a l discriminations than non-lesioned animals. Dendritic Arborization The f i n a l purpose of t h i s study was to t e s t ideas of modality interdependence and intermodal compensation at an anatomical l e v e l . Dendritic p r o l i f e r a t i o n may be a general mechanism supporting behavioral change (Greenough, 1976, 1986; Kolb, 1989). Rearing condition was found to have a s i g n i f i c a n t impact on d e n d r i t i c arborization, but only f o r a p i c a l dendrites. In comparison to dark-rearing, environmental enhancement through rearing i n a complex environment increased a p i c a l d e n d r i t i c branching i n somatosensory, v i s u a l , and auditory cortex. These findings extend previous reports of increased d e n d r i t i c branching i n animals reared i n complex environments (Greenough & Juraska, 1979; Greenough & Volkmar, 1973; Juraska, 1990; Rosenzweig & Bennett, 1978). 79 To give a more complete picture of the intermodal e f f e c t s of dark-rearing, i t would be i n t e r e s t i n g to ra i s e DR rats i n the enclosed complex environment. Although input to the v i s u a l system would s t i l l be r e s t r i c t e d , input to remaining sensory systems would be enhanced. This could p o t e n t i a l l y impact on the development of these sensory modalities, possibly decreasing the e f f e c t of dark-rearing. Long term dewhiskering through cauterization also led to an increase i n d e n d r i t i c branching, but only f o r CR animals. In comparison to other rearing conditions, there was an increase i n higher order a p i c a l d e n d r i t i c branching f o r the CR cauterized group i n a l l three c o r t i c a l areas measured. The differences may be confined to higher order branches because the lower order branches are more f u l l y developed at the time d i f f e r e n t i a l rearing begins (Greenough & Volkmar, 1973). These r e s u l t s provided anatomical evidence f o r modality interdependence. Long-term t a c t i l e r e s t r i c t i o n through cauterization led to increased higher order d e n d r i t i c branching i n auditory and v i s u a l cortex. This finding i s consistent with two hypotheses about early experience and perceptual development: 1) decreased competition during development from an early developing system ( i n t h i s case the somatosensory system) leads to increased competency i n a l a t e r developing modalities (Burnstine et a l , 1984; Turkewitz 4 Kenny, 1982); and 2) behavioral demand i s a s i g n i f i c a n t factor i n determining the impact of early somatosensory r e s t r i c t i o n (Burnstine et a l , 1984). Neurons and neural connections are i n competition with 80 each other for space and s u r v i v a l (Kaas, 1987). Experience activates and reinforces c e r t a i n pathways, while others f a l l into disuse. Those not used by the system are gradually eliminated (Aoki & Siekevitz, 1988; Kolb & Whishaw, 1989). As d e n d r i t i c p r o l i f e r a t i o n has been proposed to be a general mechanism supporting behavioral change (Kolb, 1989; Kolb & Whishaw, 1989), increasing behavioral demand may be a s i g n i f i c a n t factor i n compensation f o r early damage. The r e s u l t f o r somatosensory cortex provides evidence for intramodal compensation f o r early sensory r e s t r i c t i o n . The p r e v a i l i n g view i s that d e n d r i t i c arborization i s decreased by decreasing afferents to the cortex (Juraska, 1986, Kolb & Whishaw, 1989; Rosenzweig, Bennett & Diamond, 1972). If afferents are removed early i n l i f e , and d e n d r i t i c atrophy f a i l s to occur, then an increase i n afferent stimulation from other sources i s maintaining the d e n d r i t i c i n t e g r i t y (Kolb & Whishaw, 1989). Since cauterization represents only p a r t i a l deafferentation of a l l somatosensory afferents, the increase i n higher order branching i n somatosensory cortex may be supported by increased stimulation from other somatosensory afferents, undamaged by early cauterization. I t i s reasonable to assume that anatomical changes are manifested behaviorally. CR rats were found to show increased d e n d r i t i c branching i n comparison to DR rat s i n a l l c o r t i c a l areas measured. This difference was r e f l e c t e d i n the behavioral r e s u l t s . On tasks where there were s i g n i f i c a n t differences i n l e v e l of performance, DR rats were generally worse o f f than were 81 CR r a t s . Given the extreme difference i n rearing condition, however, these differences may not have been as great as one might expect. The behavioral data c o l l e c t e d i n t h i s study did not completely p a r a l l e l the anatomical r e s u l t s found f o r cauterized r a t s . Under anatomical examination, CRC rats showed increased branching o v e r a l l i n auditory cortex, and higher order i n auditory and somatosensory cortex. On behavioral measures, they did not d i f f e r s i g n i f i c a n t l y from other groups. These r e s u l t s may be r e f l e c t i v e of the behavioral t e s t s used i n t h i s study not being s e n s i t i v e enough to detect subtle differences that may follow cauterization. Conclusions At the anatomical l e v e l , the present study provides limited support f o r the idea of intermodal compensation following r e s t r i c t i o n of an early developing sensory modality. Animals experiencing early r e s t r i c t i o n to the t a c t i l e system through cauterization of the v i b r i s s a e show increased higher order branching i n a l l sensory c o r t i c a l areas measured. Decreasing competition during development leads to increased competency i n l a t e r developing modalities. This difference, however, i s present only when behavioral demand i s augmented through rearing in a complex environment, i n d i c a t i n g that rearing environment i s a s i g n i f i c a n t f a c t o r i n determining the impact of early somatosensory r e s t r i c t i o n . Although the anatomical differences due to early stimulation h i s t o r y were not mirrored by behavioral differences, 82 conducting anatomical and behavioral examinations i n conjunction with each other w i l l r e s u l t i n a clear e r picture of the rel a t i o n s h i p between the brain and behavior (Kolb & Whishaw, 1989). U t i l i z i n g better behavioral assays of these s e l e c t i v e c o r t i c a l lesions w i l l c e r t a i n l y help. 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