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A behavioural examination of the intramodal and intemodal consequences of long-term tactile restriction… Symons, Lawrence André 1988

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A BEHAVIOURAL EXAMINATION OF THE INTRAMODAL AND INTERMODAL CONSEQUENCES OF LONG-TERM TACTILE RESTRICTION BY VIBRISSAE REMOVAL IN RATS By Lawrence Andre Symons B.A., The U n i v e r s i t y of B r i t i s h Columbia, 1985 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 P s y c h o l o g y ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g 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 1988 (c) Lawrence Andre Symons, 1988 In p r e s e n t i n g this thesis in part ia l f u l f i lmen t o f t h e requ i remen ts fo r an a d v a n c e d d e g r e e at t h e Univers i ty o f Bri t ish C o l u m b i a , I agree that t h e Library shall m a k e it f ree ly available fo r re ference and s tudy . I f u r the r agree tha t pe rmiss ion fo r ex tens ive c o p y i n g o f th is thesis fo r scholar ly p u r p o s e s may be g r a n t e d by the h e a d o f m y d e p a r t m e n t o r b y his o r her representa t ives . It is u n d e r s t o o d that c o p y i n g o r pub l i ca t i on o f th is thesis fo r f inancia l ga in shall n o t b e a l l o w e d w i t h o u t m y w r i t t e n pe rm iss ion . D e p a r t m e n t o f P s y c h o l o g y  T h e Univers i ty o f Brit ish C o l u m b i a 1956 M a i n Ma l l Vancouve r , Canada V 6 T 1Y3 D a t e A u g . 2St lQfifi  DE-6(3 /81) A B S T R A C T A BEHAVIOURAL EXAMINATION OF THE INTRAMODAL AND INTERMODAL CONSEQUENCES OF LONG-TERM TACTILE RESTRICTION BY VIBRISSAE REMOVAL IN RATS. by Lawrence Andre Symons Despite the extensive work done on the neural consequences of t a c t i l e r e s t r i c t i o n very l i t t l e is known about the behavioural consequences of th i s manipulation. In the present investigation, an assessment was made of the effects of early, long-term t a c t i l e r e s t r i c t i o n by b i l a t e r a l removal of the mystacial vibrissae on the subsequent somatosensory capacities of rats ( i . e . the intramodal consequences) as well as i t s effects on visu a l and s p a t i a l capacities ( i . e . the intermodal consequences). As well, rearing environment (enriched vs. normal) and type of surgery (vibrissae removal by cauterization of f o l l i c l e s or by plucking) were examined to determine s p e c i f i c factors that might influence the eff e c t of early, long-term vibrissae removal. Five tasks were used to assess these e f f e c t s . The f i r s t two tasks assessed the intermodal consequences of vibrissae removal. Visual competence was assessed by measuring the habituation of orientation to repeated vi s u a l stimuli and the i i i dishabituation to subtle changes in these s t i m u l i . A version of the Morris (1981) water maze was used to assess the ra t s ' s p a t i a l a b i l i t i e s . The results of these two tasks revealed limited evidence for intermodal e f f e c t s . In terms of habituation to vis u a l orientation, rats that had had their vibrissae removed by cauterization and were subsequently reared with d a i l y access to an enriched environment required more t r i a l s to habituate to the presentation of repeated v i s u a l s t i m u l i . As well, these rats were the only group to dishabituate to a subtle change in the s t i m u l i . No e f f e c t of vibrissae removal was found in the s p a t i a l task, and environmental enrichment during development enhanced performance on this task, apparently through increased attention to d i s t a l cues by rats reared in t h i s condition. The remaining three tasks assessed the motoric and somatosensory effects of t a c t i l e r e s t r i c t i o n . No e f f e c t was found on the performance of the Puzzle Latch Box test in which the rats were required to manipulate various latches to obtain a food reward. As well, no s i g n i f i c a n t e f f e c t was observed in reactions to the tying of pieces of wire to the rats' wrists. However, early, long-term vibrissae removal (by cauterization of f o l l i c l e s or by plucking) attenuated orientation to contacts of the mystacial pad i t s e l f . This effect was dissociated from t a c t i l e r e a c t i v i t y ; a l l rats exhibited eye-flinch responses to taps on t h i s area. These results suggest that early, long-term t a c t i l e r e s t r i c t i o n has s i g n i f i c a n t behavioural consequences for the iv somatosensory system as well as the v i s u a l system. These data also provide limited evidence for theories of modality interdependence as well as yielding basic information concerning the role of the mystacial v i b r i s s e in the behaviour of the rat. Richard C. Tees, Ph.D. V TABLE OF CONTENTS Introduction 1 Rationale 15 Methods 21 Visual Orientation Task 26 Spatial Memory Task 32 Manipulatory Behaviour ...36 Bracelet Task 38 Snout Contact Orientation 38 Results 39 Visual Orientation Task 39 Spatial Behaviour 44 Puzzle Latch Box.... 52 Bracelet Task 52 Snout Contact Orientation 59 Discuss ion 62 Conclusions 71 References 74 vi LIST OF TABLES Table A The number of subjects assigned to each condition 25 Table B Description of the t r i a l s in the water maze task. (Cue postion and platform position are described. A schematic drawing showing the quadrant posistions appears in upper right corner) 35 Table C Mean number of t r i a l s in which orientation occurred for the three v i s u a l s t i m u l i . Solid display in t r i a l s 1-10; rapidly flashing display in t r i a l s 11-20; slowly flashing display in t r i a l s 21-30 43 Table D Percentage of enriched and normally reared animals that contacted the cue in the "incorrect" quadrant on t r i a l s 7 and 8 51 Table E Method of manipulation used to open the three latch types (A=butterfly latch; B=bolt latch; C=shielded b u t t e r f l y latch--see F i g . 7. Numbers represent percentage of animals using that manipulation.) 56 v i i LIST OF FIGURES Fi g u r e 1 The ontogenetic sequence of emergence of four sensory systems. (From G o t t l i e b , 1983) 7 F i g u r e 2 Diagram of the apparatus used to t e s t v i s u a l or i e n t a t ion 28 F i g u r e 3 Schematic of the p r e s e n t a t i o n of v i s u a l s t i m u l i d u r i n g the t h i r t y t r i a l s i n the v i s u a l o r i e n t a t i o n task 30 F i g u r e 4 Mean su p p r e s s i o n r a t i o s f o r r a t s i n a l l c o n d i t i o n s . T r i a l s 1-10: s o l i d d i s p l a y . T r i a l s 11-20: r a p i d l y f l a s h i n g d i s p l a y . T r i a l s 21-30: s l o w l y f l a s h i n g d i s p l a y . (A s u p p r e s s i o n r a t i o of zero i n d i c a t e s complete s u p p r e s s i o n of l i c k i n g whereas a s u p p r e s s i o n r a t i o of 0.5 r e p r e s e n t s no s u p p r e s s i o n of l i c k i n g ) 41 F i g u r e 5 Latency i n seconds to 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 f o r a l l c o n d i t i o n s 47 F i g u r e 6 Latency i n seconds to 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 f o r a l l e n r i c h e d and normally reared animals 49 v i i i Figure 7 Latencies in seconds to open latches. ("ENRICHED" and "NORMAL" refer to rearing environment; "C" and "P" refer to cauterized surgical procedure and plucked surgical procedure respectively.) 54 Figure 8 Panel A: Panel B: Latency in seconds to contact the wire bracelets. Latency in seconds to remove one of the wire bracelets. ("ENRICHED" and "NORMAL" refer to rearing environment; "C" and "P" refer to cauterized surgical procedure and plucked surgical procedure respectively.) 58 Figure 9 Frequency of orientations to l i g h t taps on the snout with a sur g i c a l swab according to condition. ("ENRICHED" and "NORMAL" refer to rearing environment; "C" and "P" refer to cauterized s u r g i c a l procedure and plucked su r g i c a l procedure respectively. ) 61 ix ACKNOWLEDGEMENTS I Thank the members of my t h e s i s committee f o r t h e i r help i n p r e p a r i n g t h i s manuscript. S p e c i a l thanks goes to t h e s i s s u p e r v i s o r , Dr. Ric h a r d Tees, f o r h i s pa t i e n c e and perseverance. I g r a t e f u l l y acknowledge the a i d of the f o l l o w i n g i n d i v i d u a l s i n h e l p i n g me get t h i s done: Mike Dunbar, Rob F a l c o n e r , Jordan Hanley, L u c i l l e Hoover, Mike Laycock, B r i a n Moorehead, Nick P f e i f f e r , and R a f a e l , whose l a s t name I've f o r g o t t e n . T h i s t h e s i s i s de d i c a t e d to my wife , G i l l i a n , without whom t h i s would not have been accomplished. 1 I n t r o d u c t i o n The e f f e c t s of e a r l y s e n s o r y e x p e r i e n c e on the development of p e r c e p t u a l c a p a b i l i t i e s and t h e i r n e u r a l s u b s t r a t e s has l o n g been one of the most i m p o r t a n t and a c t i v e t o p i c s of s t u d y f o r 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 n e u r a l and b e h a v i o u r a l p l a s t i c i t y (Greenough, 1976; M i s t r e t t a & B r a d l e y , 1978; Tees, 1976;1986). In most cases the foc u s has been on the e x a m i n a t i o n of the impact of e a r l y and/or l o n g - t e r m d e p r i v a t i o n of a s e n s o r y m o d a l i t y on subsequent i n t r a m o d a l competencies ( e . g . , M i t c h e l l & Timney, 1984). As w e l l , e x a m i n a t i o n has been made of the e f f e c t s of e a r l y or l o n g -term m u l t i m o d a l s e n s o r y enrichment on b r a i n and b e h a v i o u r (e.g. Greenough & Green, 1981). For a v a r i e t y of r e a s o n s , i n c l u d i n g the r e l a t i v e ease w i t h 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 e x p e r i e n c e i n the 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 u r s has been a prime t a r g e t of most of the i n v e s t i g a t i v e a c t i v i t y (Tees, 1976). T h i s work has been r e v i e w e d e x t e n s i v e l y (Boothe, V a s s d a l , & Schenk, 1986; M i t c h e l l and Timney, 1984; Tees, 1986). The most common method of m a n i p u l a t i n g e a r l y v i s u a l e x p e r i e n c e has been b i n o c u l a r v i s u a l d e p r i v a t i o n by e y e l i d s u t u r i n g or d a r k - r e a r i n g . The g e n e r a l f i n d i n g i s t h a t v i s u a l e x p e r i e n c e d u r i n g a " s e n s i t i v e p e r i o d " e a r l y i n ontogeny i s n e c e s s a r y f o r normal v i s u a l competence i n terms of s p e c i f i c n e u r a l (e.g. Blakemore & Van S l u y t e r s , 1975) and b e h a v i o u r a l 2 measures (e.g., Tees, 1979). Another area of recent interest i s the part played by stimulation history in the development of the somatosensory system (Kaas, Merzenick, & Killackey, 1983). While a considerable amount of work has been done on the effects of deafferentation of body surface areas of limbs or hands (e.g. Johnson, Hamilton, Hsung, & U l i n s k i , 1972), most of the research has focused on the manipulation of sensory input to the mystacial vibrissae of rodents (Gustafson & Felbain-Keramidas, 1977). The v i b r i s s a e - t a c t i l e system appears to be an extremely important source of environmental information for rodents and many other mammals. In the rat, the mystacial pad represents the single largest portion of the somatotopic map of the somatosensory cortex (Keramidas,1976). As well, the v i b r i s s a e - t a c t i l e system is highly receptotopically organized from the periphery through to the cortex (Welker, 1971; 1976). The vibrissae are arranged in rows along the snout of rodents. This organization i s followed almost exactly from the peripheral innervation to the contralateral thalamus and to area 1 of the contralateral somatosensory cortex (SmI) (Belford & Killackey, 1979). At the le v e l of the cortex (and, to a lesser extent, in the thalamus), each vibrissae projects to an individual f i e l d of c e l l s referred to as a 'barrel' because of i t s d i s t i n c t i v e shape (Woolsey & Van Der Loos, 1970). As is the case with the vi s u a l system, early deprivation has severe effects on the development of the 3 somatosensory system. In terms of neuroanatomical development, many of the effects of early r e s t r i c t i o n are analagous to the effects of binocular deprivation of the vi s u a l system (Weller & Johnson, 1975). Destruction by cauterization of the vibrissae and their receptor organs before postnatal day 5 (Weller & Johnson, 1975; Woolsey, Anderson, Wann, & Stanfield, 1979) leads to a disruption of the barrel formations in the cortex (Van Der Loos & Woolsey, 1973). While the number of neurons in the barrel f i e l d remains the same, the 'barrel' organization of the c e l l s is completely abolished (Kaas et a l . , 1983). A reduction in dendrit i c spine density in t h i s area i s also seen (Ryugo, Ryugo, & Killackey, 1975). Peripheral destruction after day 5 has been reported to have no disruptive effects on these barrel formations (Weller & Johnson, 1975). Interestingly, the effects of early t a c t i l e deprivation on the presence or absence of barrel formations appears to be e n t i r e l y dependent on the destruction of the receptor organs in the vibrissae f o l l i c l e s . Long-term c l i p p i n g (see Hand, 1982) or removal by depilatory (Weller & Johnston, 1975) of the vibrissae does not lead to disruption of the barrel formations. However, Simons and Land (1987) recently reported that although c l i p p i n g does not disrupt the cytoarchitectonic structure of the barrel formations, i t does lead to 'functional' disruption. Chronic trimming of vibrissae v i r t u a l l y abolished electrophysiological responding of c e l l s in the barrel formations corresponding to those 4 v i b r i s s a e . W hile the s t u d y of the n e u r o a n a t o m i c a l e f f e c t s of e a r l y t a c t i l e r e s t r i c t i o n has become a major a r e a of r e s e a r c h , our knowledge of the ' f u n c t i o n a l ' b e h a v i o u r a l s i g n i f i c a n c e of t h i s m a n i p u l a t i o n i s v i r t u a l l y n o n - e x i s t e n t (see G u s t a f s o n & F e l b a i n - K e r a m i d a s , 1977). A major r e a s o n f o r t h i s i g n o r a n c e i s the r e s u l t of our l a c k of u n d e r s t a n d i n g of what the v i b r i s s a e system a c t u a l l y does. Beyond s p e c u l a t i o n t h a t the v i b r i s s a e may p r o v i d e s e n s o r y i n f o r m a t i o n f o r n o c t u r n a l a n i m a l s or a n i m a l s w i t h poor v i s i o n (Boudreau & T s u c h i t a n i , 1972) v e r y l i t t l e s y s t e m a t i c r e s e a r c h has been performed on t h i s system. G u s t a f s o n and F e l b a i n - K e r a m i d a s (1977) do make a number of undocumented o b s e r v a t i o n s on the e f f e c t s of e a r l y v i b r i s s e c t o m y on b e h a v i o u r . V i b r i s s e c t o m i z e d a n i m a l s show f a s t e r t r a n s i t s of a b a l a n c e beam and d e c r e a s e d t h i g m o t a x i c b e h a v i o u r compared w i t h c o n t r o l s . These a u t h o r s s p e c u l a t e t h a t these e f f e c t s may r e s u l t from a s h i f t t o the use of v i s u a l cues i n the t a c t i l e - r e s t r i c t e d a n i m a l s . While i t might be e x p e c t e d t h a t s e n s o r y i n p u t p l a y s an i m p o r t a n t r o l e i n normal i n t r a m o d a l development, some t h e o r i s t s have r e c e n t l y suggested t h a t d i f f e r e n t i a l e x p e r i e n c e i n one m o d a l i t y might a l s o have consequences f o r the development of o t h e r s e n s o r y systems (e.g. B u r n s t i n e , Greenough, and Tees, 1984; G o t t l i e b , 1971; Tees, 1976; T u r k e w i t z and Kenny, 1982). The concept of m o d a l i t y i n t e r d e p e n d e n c e i s by no means new, however. B e r k e l e y d e s c r i b e d the n e c e s s i t y of i n t e r m o d a l e x p e r i e n c e f o r the development of s p a t i a l p e r c e p t i o n i n 1709. As w e l l , t h e r e 5 are numerous apocryphal reports of heightened auditory or t a c t i l e a b i l i t i e s in blind individuals (see Burnstine et a l . , 1984). This second area of interest--the impact of stimulation history in one modality on the c a p a b i l i t i e s of another--has been the brunt of the more recent writings concerning modality interdependence. Much of th i s interest by developmental psychobiologists has been spurred by the writings of Gottlieb and of Schneirla. Gottlieb's (1971;1976) seminal works described the pattern of ontogeny of mammalian and avian sensory functions. In a l l cases examined he found an invariant sequence of emergence of the onset of function of the modalities: t a c t i l e development occurred f i r s t followed, in order, by vestibular, olfactory, auditory, and v i s u a l development (see f i g . 1). It may be the case that t h i s sequence of emergence allows for the independent and isolated development of each sensory system, making modality interdependence in development unlike l y . However, Schneirla (1965) proposed that c o n t i n u i t i e s in development exist ; the organization of one modality may be dependent upon the l e v e l of organization of an already established modality. Turkewitz, G i l b e r t , and Birch (1974) and Turkewitz and Kenny (1982) have proposed that the widespread appearance of thi s sequential development of sensory systems might have emerged because, as a r e s u l t , competition is reduced between sensory systems, allowing each system to develop in r e l a t i v e independence. As well, t h i s sequence of development allows later-maturing systems to u t i l i z e information from those 6 F i g u r e 1. The o n t o g e n e t i c sequence of emergence of f o u r s e n s o r y systems. (From G o t t l i e b , 1983). ONTOGENETIC SEQUENCE OF DEVELOPMENT Of FOUR SENSORY SYSTEMS Per iod of D e v e l o p m e n t / X " o» Entire Sy i lem ej immolron O N S E T " ronge ot . n d . v d u o l / \ T r o c k i n g D . K r . m . n o l . o n e l T v o r i o b i l i t y unknown or ien ta to rv inhib i t ion or eic i tot ion ct ongomg activi ty A U 0 I T O * Y l o c a l i s a t i o n D t t c r i m i n o f ion • ! < . o n c n r o t * o n i n h i b i t i o n or e i o t o t t o n of onao«no, O C t t v i f y VESTIBULAR ^/^S^ P o t t - R o t a t i o n o l H«od N y t t o g m w i Ocu lo r N y t t o g m u t »»C O ' W t a t i o n or r i g h t i n g C U T A N C O U S Spr«od of Sensit ivi ty t o R* i t o ' l o d y »»c oro l or m o v t r*gH)n »*n»itiv« 8 already developed (Turkewitz & Kenny, 1982). The underlying assumption of th i s position is that competition between modalities can, and does occur. The sequential development of systems allows e a r l i e r developing systems to organize themselves in r e l a t i v e (but not complete) independence and later systems to be assimilated into the now established frameworks. Based on this argument, disruption of one modality can have consequences for the development of another. Reduction of input to one modality should lead to decreased competition for a spared modality, thus leading (possibly) to increased competence of the l a t t e r . Another p o s s i b i l i t y is that r e s t r i c t i o n of an early developing modality w i l l disrupt the "organizational framework" that a later emerging modality may need for i t s own development. In th i s second case, a decline in competence of the later developing system would be predicted. There is some evidence that competition is a powerful force in ontogeny. In terms of the intramodal consequences of deprivation, Hubel and Wiesel (1963) showed that monocular deprivation had a much more severe and long-lasting e f f e c t than binocular deprivation. These researchers and others have since shown that t h i s e f f e c t is due to decreased competition from the deprived eye, thus allowing the non-deprived eye to 'gain control' of the other's c o r t i c a l areas (cf. Cynader, 1979). Monocular deprivation has been shown to give the non-deprived eye a perceptual advantage as well--at least in terms of vernier acuity (Freeman & Bradley, 1980). Intramodal competition is also found in the development of 9 the somatosensory system of mice. As mentioned p r e v i o u s l y , removal of s e l e c t v i b r i s s a e from the m y s t a c i a l pad of mice leads to the d i s r u p t i o n of t h e i r b a r r e l formations i n the somatosensory co r t e x (Van Der Loos & Woolsey, 1973) . The remaining v i b r i s s a e ' s " b a r r e l " formations move i n t o the re g i o n s t h a t would have been occupied by the d e p r i v e d v i b r i s s a e ( H a r r i s & Woolsey, 1981; K i l l a c k e y & Erzurumlu, 1982). Evidence i s a l s o a v a i l a b l e t h a t intermodal c o m p e t i t i o n i s a l s o a s i g n i f i c a n t f a c t o r i n ne u r a l development. For example, Cynader (1979), i n examining s i n g l e u n i t r e c o r d i n g s of c e l l s i n the s u p e r i o r c o l l i c u l u s (SC) of c a t s , found t h a t d a r k - r e a r i n g had a s i g n i f i c a n t e f f e c t on some v i s u a l l y - d r i v e n c e l l s . C e l l s i n the s u p e r f i c i a l l a y e r s of the SC continued to be d r i v e n by v i s u a l i n p u t . However, i n the deeper r e g i o n s , where multimodal u n i t s are mostly found, dark-r e a r i n g v i r t u a l l y a b o l i s h e d the presence of v i s u a l l y d r i v e n c e l l s while the percentage of c e l l s d r i v e n by other m o d a l i t i e s i n c r e a s e d (Rauschecker & H a r r i s , 1983). Cynader (1979) i n t e r p r e t e d t h i s f i n d i n g as r e s u l t i n g from a competitive advantage gained by the a u d i t o r y and somesthetic inputs to the r e g i o n as a f u n c t i o n of the l o s s of v i s u a l s t i m u l a t i o n . Ryugo, Ryugo, Globus, and K i l l a c k e y (1975) found s i m i l a r e f f e c t s a t the l e v e l of the c o r t e x . For example, b l i n d i n g r a t s a t b i r t h y i e l d e d an inc r e a s e d d e n s i t y of d e n d r i t i c s p i n e s i n the a u d i t o r y c o r t e x of those animals 25 days l a t e r . Ryugo et a l . (1975) a l s o found evidence of intermodal 10 consequences re s u l t i n g from t a c t i l e r e s t r i c t i o n . Cauterization of v i b r i s s a f o l l i c l e s at b i r t h led to augmented dendritic spine density in the auditory cortex but not the v i s u a l cortex. While Ryugo et a l . (1975) proposed that these intermodal effects may be i n i t i a l l y limited to the auditory cortex due to i t s e a r l i e r development, Burnstine et a l . (1984) have speculated that their results might be due to the r e l a t i v e l y slow development of compensatory e f f e c t s . Since Ryugo et a l examined their animals at a very young age (25 days), the effects on v i s u a l cortex may well have been seen in the case of older tactile-deprived ra t s . Indeed, v i s u a l cortex thickening has been seen in adult rats (270 days of age) subjected to long-term dewhiskering (Keramidas, 1976) The behavioural evidence for intermodal competition i s somewhat less convincing. Burnstine et a l (1984) in an extensive review of both the human and animal l i t e r a t u r e , found that, in general, the hypothesis of intermodal competition after early unimodal deprivation is borne out. For instance, rats blinded at b i r t h have been shown to perform better on a non-spatial auditory learning task than rats blinded at adulthood or sighted control animals (Spigelman & Bryden, 1967). However, Tees and Cartwright (1972) found that dark-reared rats were not s i g n i f i c a n t l y handicapped nor any better at learning a simple conditioned avoidance response to auditory s t i m u l i . As well, others have reported no v i s u a l d e f i c i t s or enhancements due to auditory deprivation (MacDougall & Rabinovitch, 1971). The range of 11 tests employed in studying these e f f e c t s , however, leaves a l o t to be desired. There is also fragmentary behavioural evidence concerning the intermodal influence of t a c t i l e deprivation. Keramidas (1976) in accordance with the v i s u a l cortex data discussed previously, found that long-term dewhiskering of rats led to faster learning of a v i s u a l form discrimination (triangle vs square) and a grating discrimination (2.2 cm vs 1.6 cm stripes) on a jumping stand task. As well, Turkewitz, Gi l b e r t , and Birch (1974) found e a r l i e r and superior performance on a v i s u a l c l i f f task in cats that had had their vibrissae clipped from b i r t h . However, as Turkewitz et a l note, since a control group of animals that was clipped at the time of testing was not run, the results may be due to the intact cats choosing to use t a c t i l e before v i s u a l information (cf. Schiffman, Lore, Passafuime, and Neeb, 1970). Thus the results may be attributed to differences in the information available at the time of testing rather than to actual differences in attention or competency. Approaching the issue from a somewhat d i f f e r e n t angle, Kenny and Turkewitz (1986) examined the effects of premature visua l stimulation on the homing behaviour of rat pups. Their reasoning was that since homing behaviour came under the control of d i f f e r e n t sensory systems as they emerged, premature v i s u a l stimulation (through surgically-induced eyelid opening) may lead to a disruption in the behaviour due to precocious competition with the senses normally used to guide the behaviour. Early eye-opening led to an e a r l i e r use 12 of v i s u a l cues and a decrease in olfactory a b i l i t i e s . Thus, in terms of the intermodal competition hypothesis, early eye-opening has s i g n i f i c a n t e f f ects in the development of other modal i t ies. There i s , then, some evidence for one of the hypotheses regarding modality interdependence (Turkewitz & Kenny, 1982). Reduction of input in one modality, does, in most cases, lead to increased competence in the processing a b i l i t i e s of other modalities. This e f f e c t appears to be mediated by competitive interactions. However, the evidence is incomplete and sometimes contradictory. Fragmentary evidence also exists for the second hypothesis of Turkewitz and Kenny's (1982) proposition. Based on Schneirla (1965), they proposed that disruption of a modality necessary for the i n i t i a l development of an "organizational framework" for a behaviour might adversely a f f e c t the subsequent l e v e l of competence of that behaviour even in response to signals in other modalities (Burnstine et a l . , 1984). An important assumption of th i s model i s that disruption would presumably be most e f f e c t i v e early in ontogeny, before an organizational framework i s f u l l y established. The evidence for th i s hypothesis comes primarily from studies of s p a t i a l behaviour. Spigelman demonstrated that early-blinded rats performed more poorly than sighted or late-blinded rats in an auditory l o c a l i z a t i o n task (Spigelman, 1969; Spigelman & Bryden, 1967). Similar results have been found for performance on the Hebb-Williams maze (Hebb, 1947). Tees, Midgley, and 13 N e s b i t (1981) a l s o found t h a t d a r k - r e a r i n g had an adverse e f f e c t on l e a r n i n g i n a 17-arm r a d i a l maze. Burnsti n e et a l ' s (1984) review of the human l i t e r a t u r e a l s o f o l l o w s the same theme: e a r l y b l i n d are poorer at s p a t i a l tasks than l a t e b l i n d or s i g h t e d s u b j e c t s . Some i n c o n s i s t e n c i e s do e x i s t , however. Gamboni (1964) found that dark-reared r a t s perform b e t t e r on a Krech hypothesis maze than l i g h t - r e a r e d c o n t r o l s . A l s o , Sutherland and Dyck (1984) found t h a t e a r l y b l i n d i n g l e d to improved l e a r n i n g of an a u d i t o r y v e r s i o n of the Morris (1981) water maze. F i n a l l y , Meyer, Feo Ramos, and F e r r e s - T o r r e s (1976) r e p o r t e d i n c r e a s e d d e n d r i t i c spine d e n s i t y i n the CAl hippocampus and dentate gyrus of dark-reared r a t s . Both these areas have been i m p l i c a t e d i n s p a t i a l behaviour (O'Keefe & Nadel, 1978). I t i s i n t e r e s t i n g to note t h a t there are v i r t u a l l y no s t u d i e s concerning the e f f e c t s of d e p r i v a t i o n of m o d a l i t i e s other than v i s i o n on s p a t i a l behaviour. T h i s may be due to the importance most t h e o r i s t s place on v i s i o n f o r the development of s p a t i a l a b i l i t i e s (e.g. Gibson, 1969). Als o the adverse e f f e c t s due to v i s u a l d e p r i v a t i o n seen by some re s e a r c h e r s i s somewhat c o n t r a d i c t o r y to the hypothesis proposed by Turkewitz and Kenny (1982). In t h i s case, a l a t e d e v e l o p i n g modality appears to be p r o v i d i n g i n f o r m a t i o n f o r e a r l i e r ones (Burnstine et a l . , 1984). Most r e s e a r c h e r s a t t r i b u t e the e f f e c t s of v i s u a l d e p r i v a t i o n on s p a t i a l behaviour to the a t t e n u a t i o n of c o r t i c a l development seen i n v i s u a l l y d e p rived animals (see Tees et a l . , 1979). However, 14 the hypothesis of Turkewitz and Kenny (1982) is that disruption of an e a r l i e r developing system (and, therefore, i t s organizational framework) should lead to disruptions in later developing systems. While i t c e r t a i n l y may be the case that appropriate vis u a l functioning is the necessary precursor to normal s p a t i a l behaviour, no systematic study of the e f f e c t s of e a r l i e r developing modality r e s t r i c t i o n on s p a t i a l behaviour has been performed. Another aspect of intermodal competition that has not been systematically explored i s the role that behavioural demand might play (Burnstine et a l . , 1984). In most of the animal studies, the animals were reared in r e l a t i v e l y environmentally impoverished conditions. As Burnstine et a l . (1984) note, the laboratory cage does not correspond very well with the complex world encountered by deaf or blind humans. Behavioural demand i s an important requisite of normal sensorimotor development (Hein, 1980; Held and Hein, 1963). As well, increased demand, through environmental enrichment, has s i g n i f i c a n t e f f ects on c o r t i c a l c e l l development (Greenough & Green, 1981), overal l brain si z e , and c o r t i c a l a c t i v i t y (Rosenzweig & Bennett, 1978). These effects occur only after actual behavioural interaction with the enriched environment. Ferchmin, Bennett, and Rosenzweig (1975) found no s i g n i f i c a n t c o r t i c a l a c t i v i t y differences between animals placed inside enclosures in enriched environments and normally cage reared animals. There is some evidence that behavioural demand may play a role in intermodal competition. Krech, Rosenzweig, and 15 Bennett (1963) found t h a t n e o n a t a l l y b l i n d e d r a t s r a i s e d i n complex environments had a heavier somesthetic c o r t e x and i n c r e a s e d a c e t y l c h o l i n e s t e r a s e a c t i v i t y i n n o n - v i s u a l c o r t i c a l areas than s i g h t e d r a t s r a i s e d i n s i m i l a r environments. The b e h a v i o u r a l s i g n i f i c a n c e of t h i s r e s u l t i s s p e c u l a t i v e , but given the evidence from other sources t h a t environmental enrichment leads to improved performance i n a v a r i e t y of tasks (e.g. Forgus, 1954; Greenough, Madden, & Fleischmann, 1972; Juraska, Henderson, and M u l l e r , 1984), i t seems l i k e l y t h a t the e f f e c t s found by Krech et a l . (1963) may be of some f u n c t i o n a l importance. I n t e r e s t i n g l y , Krech et a l (1963) a l s o found t h a t the enucleated e n r i c h e d , animals had heavier v i s u a l c o r t i c e s than the r e s t r i c t e d , non-sighted c o n t r o l s . T h i s f i n d i n g suggests t h a t some ' f u n c t i o n a l r e a l l o c a t i o n ' (Burnstine et a l , 1984) may be o c c u r r i n g . The v i s u a l areas may be p r o c e s s i n g i n f o r m a t i o n from other m o d a l i t i e s . F i n a l l y , Burnstine et a l . (1984) rep o r t e d an unpublished study that found t h a t b l i n d e d mice r a i s e d i n e n r i c h e d environments showed a w h i s k e r - t r i g g e r e d p l a c i n g response at a f u r t h e r d i s t a n c e than s i g h t e d c o n t r o l s . Rat i o n a l e The evidence f o r the modality-interdependence model proposed by Turkewitz, G i l b e r t , and B i r c h (1974) and Turkewitz and Kenny (1982) i s suggestive but incomplete. The present study i s a d i r e c t t e s t of the two main hypotheses a r i s i n g from t h i s model: 1) t h a t e a r l y r e s t r i c t i o n of one 16 modality w i l l lead to compensation (Burnstine et a l . , 1984) in another modality; and 2) that early r e s t r i c t i o n of sensory input in one modality might disrupt the 'organizational framework' of a behaviour that i s required for appropriate subsequent competence in another modality. The test involves examining the effects of early t a c t i l e r e s t r i c t i o n through disruption of the mystacial vibrissae of rats . Vibrissae are present in a l l rodents and many other mammals, suggesting i t s important contribution to the fitness of these species. As mentioned previously, the mystacial pad is the single largest part of the somatotopic map of the somatosensory cortex of the rat (Keramidas, 1976), and the vibrissae t a c t i l e system is highly organized at a l l levels of projection from the periphery to the cortex (Welker, 1971; 1976). These facts i l l u s t r a t e the extreme (al b e i t poorly understood) importance of thi s system to the rat. Given th i s evidence, the excellent physiological evidence and the fragmentary behavioural evidence, i t seems l i k e l y that disruption of thi s system would have important consequences for developing ra t s . Also, the t a c t i l e system is the e a r l i e s t emerging sensory modality (Gottlieb, 1971). Thus, disruption of thi s system d i r e c t l y examines the second ( i . e . 'organizational framework') hypothesis of Turkewitz and Kenny (1982). Presumably, i f disruption of the t a c t i l e system hinders the development of some framework (e.g. for s p a t i a l behaviour--Bogardus & Henke, 1911) then performance in subsequently emerging modalities should be impaired. Also, since i t is 17 e s t a b l i s h e d t h a t p e r i p h e r a l t a c t i l e r e s t r i c t i o n l e a d s , at the ver y l e a s t , to a b o l i s h e d n e u r a l a c t i v i t y (Simons & Land, 1987), i t seems l i k e l y t h a t t h i s manipulation w i l l give other m o d a l i t i e s a 'competitive advantage' i f the in t e r m o d a l -c o m p e t i t i o n hypothesis i s t e n a b l e . In accordance with the s p e c u l a t i o n s of Burnsti n e et a l . (1984), the present study a l s o examines the r o l e of b e h a v i o u r a l demand i n intermodal c o m p e t i t i o n . B e h a v i o u r a l demand i s augmented by a l l o w i n g some animals d a i l y access to an e n r i c h e d environment. F i n a l l y , a p r e l i m i n a r y examination i s made of the b e h a v i o u r a l consequences of t a c t i l e r e s t r i c t i o n r e s u l t i n g from r e c e p t o r d i s r u p t i o n (by f o l l i c u l a r c a u t e r i z a t i o n ) as opposed to r e s t r i c t i o n of t a c t i l e input (by long-term c l i p p i n g ) . In order to assess the consequences of these manipulations, a b a t t e r y of t e s t s was used. The advantages of such an approach have been o u t l i n e d p r e v i o u s l y (Kolb & Whishaw, 1983; Whishaw, Kolb, & Sutherland, 1983) and i t s e f f e c t i v e n e s s i l l u s t r a t e d i n the work of these r e s e a r c h e r s i n t h e i r assessment of the e f f e c t s of b r a i n damage i n r a t s . B r i e f l y , the premise of such an approach i s t h a t s e v e r a l d i f f e r e n t t e s t s of behaviours that animals are l i k e l y to engage i n spontaneously are more l i k e l y to y i e l d i n t e r p r e t a b l e r e s u l t s than would a s i n g l e t e s t . The present study employed f i v e t a s k s . 1. A task developed by Midgley and Tees (1981; 1983) to assess o r i e n t a t i o n to v i s u a l s t i m u l i wasis used as a t e s t of the 18 i n t e r m o d a l - c o m p e t i t i o n h y p o t h e s i s . T h i s t a s k measures h a b i t u a t i o n t o the r e p e a t e d p r e s e n t a t i o n of v i s u a l s t i m u l i and d i s h a b i t u a t i o n t o s u b t l e changes i n these s t i m u l i . Performance on t h i s t a s k appears t o be mediated by a t t e n t i o n a l f a c t o r s r a t h e r than p r o c e s s i n g c a p a b i 1 i t i e s - -d a r k - r e a r e d r a t s do show o r i e n t a t i o n t o the v i s u a l s t i m u l i , but h a b i t u a t e more q u i c k l y and are l e s s l i k e l y t o d i s h a b i t u a t e t o s t i m u l u s changes ( M i d g l e y & Tees, 1983). I t has been suggested t h a t i n t e r m o d a l compensation i s most l i k e l y t o be an a t t e n t i o n a l l y based phenomenon r a t h e r than an a c t u a l augmentation of p r o c e s s i n g c a p a b i l i t i e s ( B u r n s t i n e e t a l , 1984; Tees, 1976). Thus, t h i s t a s k i s an e x c e l l e n t measure of p o t e n t i a l v i s u a l compensation f o r t a c t i l e r e s t r i c t i o n . As w e l l , t h i s t a s k examines v i s u a l l y - g u i d e d o r i e n t a t i o n s o l e l y , e x c l u d i n g the use of o t h e r cues (e.g. a u d i t o r y , t a c t i l e ) t h a t may have confounded o t h e r s t u d i e s of i n t e r m o d a l c o m p e t i t i o n ( T u r k e w i t z , G i l b e r t , & B i r c h , 1974). 2. The ' o r g a n i z a t i o n a l framework' h y p o t h e s i s of T u r k e w i t z and Kenny (1982) was examined by t e s t i n g s p a t i a l b e h a v i o u r u s i n g the water maze deve l o p e d by M o r r i s (1981). In t h i s t a s k a n i m a l s a r e r e q u i r e d t o f i n d a submerged p l a t f o r m h i d d e n i n a p o o l f u l l of water u s i n g a v a i l a b l e d i s t a l or p r o x i m a l cues ( K o l b & Walkey, 1987; S u t h e r l a n d and Dyck, 1984). V a r i a t i o n s of t h i s t a s k have been used t o t e s t the ontogeny of s p a t i a l b e h a v i o u r (Rudy, S t a d l e r - M o r r i s , & A l b e r t , 1987) and 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 ( M o r r i s , 1983; K o l b & Walkey, 1987). A g a i n , t h i s t a s k i s e n t i r e l y v i s u a l l y 19 based, thus accurately assessing any differences in v i s u a l s p a t i a l behaviour due to t a c t i l e r e s t r i c t i o n . 3. A puzzle latch box was used to assess the fine motor behaviours of the t a c t i l e - r e s t r i c t e d animals. In t h i s task, the animals are required to open latches of various types in order to receive a food reward. This task has been used previously as a measure of brain damage effects (Gentile, Green, Nieburgs, Schmelzer, & Stein, 1978; Kolb & Whishaw, 1983) . 4. Another test of sensorimotor control, as well as a measure of l a t e r a l i t y , is the bracelet test developed by Schallert and his colleagues (e.g. Schallert & Whishaw, 1984) . In th i s task, pieces of wire are t i e d to the wrists of the rats, and th e i r reactions to i t are recorded. Performance on t h i s task has been shown to be sensitive to c o r t i c a l damage (Schallert & Whishaw, 1983) and is also used here as an assessment of t a c t i l e r e a c t i v i t y . 5. Orientation to snout contact was also used as a measure of t a c t i l e responsiveness. SC lesions impair performance on t h i s task ( K i r v e l , Greenfield, & Meyer, 1974), thus t h i s test was used as a measure of the e f f i c a c y of the t a c t i l e r e s t r i c t i o n techniques. As well, a second related test of t a c t i l e r e a c t i v i t y was administered. In normal rats, a sharp tap to the mystacial pad evokes an eye-flinch reponse. This test was used to determine differences between general t a c t i l e s e n s i t i v i t y and o r i e n t a t i o n t o t a c t i l e s t i m u l i . 21 Methods  Subjects The subjects were 88 male rats of the Long-Evans (Rattus  Norvegicus) s t r a i n , born and reared in the Biopsychology colonies at the University of B r i t i s h Columbia. The general rearing conditons have been described previously (Tees, 1968). The rats were a l l raised in 25 x 47 x 20 cm p l a s t i c maternity bins u n t i l 21 days of age at which time they were placed in groups of 4 to 6 in hanging wire mesh cages (66 x 25 x 18 cm). Food (Purina Rat Chow) and water were available ad libitum u n t i l the time of tes t i n g . A l l rats remained on a 12:12 hr light/dark schedule throughout the experiment, and a l l t e sting was performed during the rats' l i g h t cycle. At the time of testing the rats were separated and housed i n d i v i d u a l l y in hanging wire mesh cages (20 x 25 x 18 cm). The rats were between 350 and 600 g at the time of tes t i n g . Surgery One half of the rats underwent complete removal of their mystacial vibrissae shortly after b i r t h . In order to ensure that vibrissae removal occurred before the i n i t i a l development of the posteromedial barrel f i e l d , a l l of the experimental rats were operated on within 3 days of b i r t h (Keramidas, 1976). Two manipulations were performed: (1) plucking of the vibrissae or (2) cauterization of the 22 vibrissae f o l l i c l e s . Assignment to each condition was determined by l i t t e r , and a t l e a s t three l i t t e r s were randomly assigned to each condition. A l l rats were separated from their dams and anaesthetized with a combination of cold (ice) and Halothane vapour. The rats were maintained on ice during surgery. For the plucked group, the vibrissae were located with a dissecting microscope and i n d i v i d u a l l y pulled from the f o l l i c l e s . For the cauterization groups, each v i b r i s s a was located, and a thin (98 micrometer) wire connected to a dc lesion maker (Grass) was inserted into the f o l l i c l e . The f o l l i c l e was lesioned using a 150 V current with an intensity of 2 ma (Van Der Loos & Woolsey, 1973). The wire represented the positive source while the plate the rat rested on during the surgery was the negative source. Control rats were treated in a similar manner; however, in the case of the 'cauterization controls', a similar current was passed through the upper snout or pinnae of the rats . The plucking procedure t y p i c a l l y inhibited regrowth of vibrissae in the young rats for approximately 1 week. At this time, in order to avoid repeated anaesthetization, the rats' vibrissae were shaved using an Oster small animal shaver with a size 40 head. Shaving continued twice weekly u n t i l the time of tes t i n g . 23 Environments and Rearing Conditions Starting at the age of 21 days, the l i t t e r s assigned to the enriched condition were given d a i l y access in groups of 7 to 12 for 1 to 2 hours to an elaborate open f i e l d . This d a i l y period of enriched environment exposure has been reported to have an e f f e c t equivalent to continuous exposure, at least in terms of some brain size measures (Rosenzweig, Love & Bennett, 1968). The open f i e l d was a t a l l , wire-mesh box (180 x 92 x 62 cm) with a Sanicel-covered floor and two Sanicel-covered bridges located approximately 19 and 39 cm above the bottom. Wire-mesh ramps connected the bridges with one-another and with the bottom of the apparatus. The open f i e l d was f i l l e d with an assortment of toys some of which were changed d a i l y (cf Greenough and Green, 1981). The control rats were also handled d a i l y and maintained in normal group cages. Design and Behavioural Tasks The general design of the study was a 2 x 2 x 2 f a c t o r i a l . The two environment types (enriched and normal) represented one factor, t a c t i l e r e s t r i c t i o n (vibrissae present or absent during development) the second factor, and type of r e s t r i c t i o n (receptor destruction vs t a c t i l e r e s t r i c t i o n by clipping) the t h i r d . The number of subjects in each group is shown in Table A. The five tasks chosen 24 Table A. The number of s u b j e c t s a s s i g n e d t o each c o n d i t i o n . Enr iched C a u t e r i s e d Enr iched C. C o n t r o l s Enr iched Plucked Enr iched P. C o n t r o l s Normal C a u t e r i z e d Normal C. C o n t r o l s Normal Plucked Normal P. C o n t r o l s 26 tested a va r i e t y of perceptual and motor behaviours. In order to avoid a possible sequencing ef f e c t confound, rats in a l l groups proceeded through the tasks in the same order. The order of task presentation was as follows. Apparatus and Procedure Visual Orientation Task The apparatus used to examine vi s u a l orientation behaviour has been described previously (Midgley & Tees, 1981, 1983) and is presented in Figure 2. Nine 4.7 mm diameter green light-emitting diodes (LEDs) were positioned in an arc 12 cm above the floor of the apparatus. A l l of the LEDs were 9 cm from the t i p of the metal water spout subtending an arc of 130 degrees from th i s point. The water spout was attached to the center of the Plexiglas panel, at 5 cm above the brass rod f l o o r . The l i g h t i n t e n s i t y of the LEDs at the spout was approximately 4.8 cd/m}. The entire apparatus was housed within a 66.2 x 66 x 50.8 cm l i g h t - and sound- attenuating box with a v e n t i l a t i o n fan that produced 60 dB (SPL) background noise. The presentation of l i g h t s and the counting of the number of l i c k s was controlled by an Comtex PC XT microcomputer using a QNX operating system. A computer program written in C language monitored the l i c k i n g and presented the vis u a l stimuli through a 96-line d i g i t a l 10 board. Water was presented through a metal tube, which was 27 F i g u r e 2. Diagram of the a p p a r a t u s used t o t e s t v i s u a l o r i e n t a t i o n . GRID FLOOR-S3 00 2 9 F i g u r e 3. Schematic of the p r e s e n t a t i o n of v i s u a l s t i m u l i d u r i n g the 30 t r i a l s i n the v i s u a l o r i e n t a t i o n t a s k . TRIALS 1-10 30 ON LEDS OFF T R I A L N 15 L I C K S 5 SEC B A S E L I N E 5 SEC TEST T R I A L N * 1 TRIALS 1 1-20 ON LEDS OFF T R I A L N 1 5 L I C K S 5 SEC B A S E L I N E 5 SEC TEST T R I A L N * 1 TRIALS 21 -30 ON LEDS OFF-T R I A L N 15 L I C K S 5 SEC B A S E L I N E 5 SEC TEST T R I A L N * 1 31 connected by a rubber tube to a t e f l o n solenoid valve. (General Valve Corp.). Each l i c k completed a c i r c u i t that opened the valve for 0.1 sees allowing approximately 0.02 ml water to pass from a reservoir into the tube and registered the l i c k with the computer. Five days prior to testing, the rats were water deprived for 24 hr and then i n d i v i d u a l l y allowed 15 min access to the apparatus with the l i c k tube c i r c u i t connected. During t h i s acclimatization period, the LEDs were disconnected. After each acclimatization period the rats were returned to their home cages and given an additional 15 min access to water. The rats were acclimatized for three days and were then tested (Midgley & Tees, 1983). Testing consisted of three blocks of ten t r i a l s . Each t r i a l began with the rat making 15 l i c k s to i n i t i a t e a 5 s baseline period. During t h i s baseline period, the number of l i c k s was recorded. The f i f t e e n t h l i c k following the baseline period i n i t i a t e d the display of l i g h t s for 5 s. The number of l i c k s was also counted during t h i s 5 s test period (see F i g . 3 for schematic). The nine l i g h t s ( s o l i d display) were turned on for the entire 5 s on t r i a l s 1 to 10. On t r i a l s 11 to 20 the l i g h t s f l i c k e r e d on and off every 0.1 s (rapidly f l i c k e r i n g d i s p l a y ) . The l i g h t s f l i c k e r e d on and off every 0.2 s (slowly f l i c k e r i n g display) on t r i a l s 21 to 30. This pattern of displays was chosen because i t had previously been shown to be the most subtle in terms of habituation and recovery of orientation (Midgley & Tees, 1983). Thus, i t i s less l i k e l y that these displays would 32 produce a floor e f f e c t and more l i k e l y that differences in orientation might be found. Orientation to the l i g h t displays was determined by the suppression of ongoing l i c k i n g during the presentation of the s t i m u l i . Suppression r a t i o s were calculated using the formula: TEST LICKS / (TEST LICKS + BASELINE LICKS). TEST LICKS was the number of l i c k s during the 5 s "stimulus on" phase of a t r i a l and BASELINE LICKS is the number of l i c k s during the preceding 5 s "stimulus o f f " baseline phase. Thus a value of zero indicated complete suppression of l i c k i n g , while a value of 0.5 represented no suppression. Rate of habituation and recovery of orientation to the l i g h t display was determined by analysing the number of t r i a l s in which the number of l i c k s during the test period represented 10% or less than the number of l i c k s during the previous baseline period. The number of t r i a l s in which t h i s c r i t e r i o n was met for each of the three sets of ten t r i a l s represented the number of t r i a l s for each stimulus ( i . e . s o l i d display, rapid flashing, slow flashing) that the rats oriented to the stimulus. Spatial Memory Task Spatial memory was evaluated using a v a r i a t i o n of the water-maze procedure developed by Morris (1981). The apparatus consisted of a c i r c u l a r p l a s t i c pool (Coleco) with a diameter of 1.3 m and a height of 28cm. The pool was f i l l e d to 21 cm with cool water (approximately 22 C) rendered 33 opaque with black watercolour paint powder (Alphacolor). The platform was a large p l a s t i c jar 19 cm t a l l and 9 cm in diameter at the l i d , covered in black p l a s t i c f i l m . Painted wire mesh was attached to the top of the jar and the jar was f i l l e d with stones for weight. A blue racquet b a l l (Deuce Court) painted with white str i p e s was used as a proximal cue and was attached by a 20 cm s t r i n g to a sheet-metal anchor. This allowed the cue to be placed on the platform or to f l o a t f r e e l y depending on the nature of the t r i a l . The entire apparatus resided in an IAC sound attenuating chamber (Model 402-A) with a number of conspicuous d i s t a l cues available. The te s t i n g consisted of 16 t r i a l s conducted over 3 days. On the f i r s t day, each rat was given two 90-s habituation t r i a l s with no platform or cue present. On the second day testing began. The second day consisted of eight t r i a l s (see Table B for a summary of the t r i a l s ) . For the f i r s t four t r i a l s , the platform was located in quadrant I (see top of Table B) and the proximal cue was placed on top of i t . On t r i a l s 5 and 6, the cue was placed in quadrant III while the platform remained in quadrant I. And on t r i a l s 7 and 8 the platform was moved beneath the cue in quadrant I I I . On the second day test t r i a l s 9 to 14 were run. T r i a l s 9 and 10 were a r e p l i c a t i o n of t r i a l s 7 and 8 after a 24 hour retention i n t e r v a l . On t r i a l s 11 and 12 the cue was removed form the pool. And on t r i a l s 13 and 14, the platform was moved to quadrant IV. The rats were released on each t r i a l from one of the four poles in a pseudorandom sequence. Escape latency in 34 Table B. D e s c r i p t i o n of the t r i a l s i n the water maze task . Cue p o s i t i o n and p l a t f o r m p o s i t i o n are d e s c r i b e d . A schematic drawing showing the quadrant p o s i t i o n s appears i n upper r i g h t corner QUADRANTS Tr i a l . 1 Tr i a l Type C l / P l C l / P l C l / P l C l / P l Descr i pt i on 35 Cue l o c a t e d on top of p l a t f o r m i n quadrant 1. Cue l o c a t e d on t o p of p l a t f o r m i n quadrant 1. Cue l o c a t e d on top of p l a t f o r m i n quadrant 1. Cue l o c a t e d on t o p of p l a t f o r m i n quadrant 1. C3/P1 C3/P1 Cue l o c a t e d i n quadrant 3. P l a t f o r m l o c a t e d i n quadrant 1. Cue l o c a t e d i n quadrant 3. P l a t f o r m l o c a t e d i n quadrant 1. C3/P3 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. 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 C3/P3 Cue l o c a t e d on top of p l a t f o r m i n quadrant 3. 24 hour d e l a y from T8 Cue l o c a t e d on top of p l a t f o r m i n quadrant 3. 11 12 -/P3 -/P3 No Cue. P l a t f o r m l o c a t e d i n quadrant 3. No Cue. P l a t f o r m l o c a t e d i n quadrant 3. 1 3 -/P4 No Cue. P l a t f o r m l o c a t e d i n quadrant 4. 14 -/P4 No Cue. P l a t f o r m l o c a t e d i n quadrant 4. 36 seconds was recorded. It was also noted whether or not the rats touched the cue during t r i a l s 5 and 6, when the cue was located in an "incorrect" quadrant. When a rat encountered the platform, i t was permitted to remain there for 60 s. If the platform was not located within 90 s, the rat was removed and given a score of 90 s. The rats were run i n d i v i d u a l l y in squads of 3 to 6. This sequence of t r i a l s allowed the testing of a number of d i f f e r e n t aspects of s p a t i a l memory and perception. F i r s t , t r i a l s in which the cue was present tested the rats' attention to l o c a l and d i s t a l v i s u a l aspects of the environment. The s h i f t i n g of the cues tested the rats' reliance on the l o c a l cue for finding the platform. The 24-hr delay represented a test of long-term retention, and the repositioning of the platform tested the extent to which d i s t a l v i s u a l cues were being u t i l i s e d to complete the task. Manipulatory Behaviour Fine motor control was assessed using a latch box similar to that used by Gentile, Green, Nieburgs, Schmelzer, and Stein (1978) and Kolb and Walkey (1987). The apparatus was a 43 x 25 x 18 cm hanging "double" wire cage with a Plexiglas p a r t i t i o n mounted at 16 cm of the length. A hinge-mounted 9 x 8 cm Plexiglas door was located in the centre of the p a r t i t i o n . On t h i s door a variety of latches could be mounted (see below). In the smaller section of the box a small food dish was located. 37 The rats were food deprived for 24 hr before testing and were given s u f f i c i e n t food each day to maintain 85 percent of their normal body weight. The testing consisted of four phases. The f i r s t phase was a pretraining period during which the rats were adapted to the apparatus and their behaviour shaped to push open the Plexiglas door to receive a Honeynut Cheerio (General Foods) reward. Once the rats r e l i a b l y opened the door within 10 s, testing commenced. The remaining three phases of testing consisted of latch manipulation. The f i r s t latch was a b u t t e r f l y wing-nut (see Fig. 7). A downward or upward diplacement of the latch by 2 cm opened the door. The next phase involved a bolt latch which required a sideward movement of the bolt or handle to open the door. The f i n a l latch was a b u t t e r f l y latch similar to the f i r s t except that i t was p a r t i a l l y covered with a 8 x 5 cm piece of Plexiglas. Only the end of the latch was manipulable by the rats. On each t r i a l , the rats were required to open the door within 120 s to gain access to the Cheerio reward. The rats were required to complete 5 t r i a l s in one day in order to move on to the next latch. The rats were run i n d i v i d u a l l y in t h e i r colony room. Total duration of manipulation of the door or latch was used as the primary dependent variable rather than latency to open the door (cf. Kolb & Walkey, 1987), since i t represented a more accurate measure of the rats' motor behaviour. As well, the predominant method of manipulating the latch ( i . e . by snout, mouth or paws) was also recorded. 38 Sensorimotor Tasks  Bracelet Test Two tasks were used to asses the sensorimotor a b i l i t i e s of the rats . The f i r s t task, the wrist-bracelet test, i s a derivation of the dot test used by Schallert and his colleagues (e.g. Schallert & Whishaw, 1984). The task was used as a measure of sensorimotor asymmetry as well as a general measure of t a c t i l e reactiveness and fine manipulatory a b i l i t i e s . A l l rats were i n d i v i d u a l l y tested in their home cages. Each rat was removed from the cage and 8 cm pieces of 22 ga. wire were t i e d around each wrist using h a l f - h i t c h knots. The wires were t i e d t i g h t l y enough to prevent them from f a l l i n g off e a s i l y and the ends of the wire were cut nearly flush to the knot. The rats were then returned to thei r home cages. Latency to contact the wires, side of f i r s t contact, t o t a l duration required to remove one of the wires and the side of f i r s t removal were a l l recorded. If the wire was not removed within 4 min, the rat was given a score of 240 s and the t r i a l was terminated. Snout Contact Orientation The second task--a measure of orientation to snout 39 contact (Whishaw, O'Connor & Dunnett, 1985)--is also a measure of t a c t i l e responsiveness and was used as an assessment of the e f f i c a c y of the t a c t i l e deprivation techniques. A l l rats were tested i n d i v i d u a l l y in dim red l i g h t (Kodak s a f e l i g h t f i l t e r No. 16). Each rat was taken from i t s home cage and placed in a 40 x 48 x 20 cm p l a s t i c bin in the testing room. After a 1-min habituation period, the rat's snout was touched with a cotton-tipped surgical swab. Six t r i a l s were run and the number of orientations to the probe was recorded. At the end of the six t r i a l s , the rat was held by the experimenter and tapped sharply on the mystacial pad with a surgical swab, and eye-flinch responses were recorded. Results Visual Orientation Task A repeated measures ANOVA was performed on the suppression r a t i o data generated by the eight groups of rats across the 30 presentations of vi s u a l s t i m u l i . This analysis revealed a s i g n i f i c a n t Rearing Environment x Surgery x Vibrissae interaction, F_( 1, 80 ) =4 . 01, p_<.05. As well, a s i g n i f i c a n t T r i a l s e f f e c t was found, F( 29, 2320 )=30 .14, p_<.01. No other s i g n i f i c a n t e f f ects were observed. A summary of the suppression ratios for a l l groups is found in F i g . 4. Unfortunately, the variances of the suppression r a t i o data was heterogeneous across group thus making these repeated-AO F i g u r e 4. Mean su p p r e s s i o n r a t i o s f o r r a t s i n a l l c o n d i t i o n s . T r i a l s 1 to 10: s o l i d d i s p l a y . T r i a l s 11 to 20: r a p i d l y f l a s h i n g d i s p l a y . T r i a l s 21 to 30: s l o w l y f l a s h i n g d i s p l a y . A s u p p r e s s i o n r a t i o of zero i n d i c a t e s complete s u p p r e s s i o n of l i c k i n g whereas a s u p p r e s s i o n r a t i o of .5 r e p r e s e n t s no s u p p r e s s i o n of l i c k i n g . 0 2 CAUTERIZED -» C CONTROL PLUCKED P CONTROL CAUTERIZED C CONTROL PLUCKED P CONTROL J h ENRICHED h NORMAL 8 10 12 14 16 18 20 22 24 26 28 30 TRIAL 42 Table C. Mean number o£ t r i a l s i n which o r i e n t a t i o n occurred f o r the three v i s u a l s t i m u l i . S o l i d d i s p l a y i n t r i a l s 1 to 10; r a p i d l y f l a s h i n g d i s p l a y i n t r i a l s 11 to 20; s l o w l y f l a s h i n g d i s p l a y i n t r i a l s 21 to 30 . Enr iched Cauter ized Enr iched C. Controls Enr iched Plucked Enr iched P. Controls Normal Cauter ized Normal C. Controls Normal Plucked Normal P. Controls Tr i a l s  1-10 5.24 3.00 4.09 3.93 3.00 3.94 4.09 4.12 Tr i a l s  11-20 1.22 0.29 0. 364 1.00 0.78 0.89 1.01 0 . 67 Tr i a l s  21-30 0.78 0.57 0.55 0.50 0.56 0 .33 0.36 0.44 44 measures ANOVA results somewhat suspect. Thus, the further analysis of the number of t r i a l s in which s i g n i f i c a n t orientation based on the c r i t e r i o n of test l i c k s being less than 10% of baseline l i c k s was used to analyse habituation and dishabituation to the three stimulus patterns. In t h i s regard, a summary of the t r i a l s on which s t a t i s t i c a l l y s i g n i f i c a n t interruption of l i c k i n g occurred is found in Table C. An analysis of variance of these data found a s i g n i f i c a n t e f f e c t for display pattern, (F(2,160)=129.8, p_<.01), as well as a s i g n i f i c a n t Rearing Environment x Surgery x Vibrissae interaction, F ( 2,160 ) =3 .12, p_< . 05 ) . As can be seen on thi s Table and in Fi g . 4, the number of t r i a l s in which s i g n i f i c a n t suppression of l i c k i n g occurred d i f f e r e d according to group. Most notably, the enriched/dewhiskered/cauterized rats appeared to be more attentive to the LED displays than rats in the other groups. Post-hoc analysis of these data (Tukey's) indicated that the enriched/dewhiskered/cauterized rats oriented on s i g n i f i c a n t l y more t r i a l s than any of the other groups to the presence of the s o l i d display of l i g h t s in the f i r s t 10 t r i a l s (p_<.05). No other s i g n i f i c a n t difference was found. Spatial Behaviour: Water Maze Task A repeated measures ANOVA was used to assess the significance of differences in escape latencies between the eight groups of rats across the 14 test t r i a l s . Long-term dewhiskering, by cauterization or by plucking, had no eff e c t 45 on s p a t i a l behaviour as measured by the water maze task, F(1,72)=.307, p_>.05. However, a s i g n i f i c a n t main eff e c t for T r i a l (F(13,936)=27.05, p_<.01) as well as a Rearing Environment x T r i a l interaction (F(13,936)=1.992, p<.05) were observed. No other s i g n i f i c a n t effects were found. The data for a l l groups are summarized in F i g . 5. Post-hoc testing revealed that, o v e r a l l , the enriched rats had s i g n i f i c a n t l y faster escape latencies on t r i a l s 1, 5, 7, and 8 and a slower escape latency on t r i a l 13 than did the normally reared rats (Tukey's HSD, a l l p_'s <.05) (see Fi g . 6 for a summary of the data based on rearing environment). It appears that the normally reared rats were disrupted by the movement of the cue to the quadrant opposite the platform on t r i a l s 5 and 6. This effect is corroborated by an analysis of the percentage of rats that made contact with the cue placed in the "incorrect" quadrant on t r i a l s 5 or 6. S i g n i f i c a n t l y more normally reared rats contacted the cue on t r i a l s 5 or 6 than did enriched rats, XJ(1)=8.851, p_<.01 (see Table D) . The p r o b a b i l i t y of touching the cue did not vary with any other factor. The normally reared rats were s i g n i f i c a n t l y disrupted on t r i a l s 7 and 8. On these t r i a l s the platform was shifted from the quadrant without the cue to the quadrant with the cue. F i n a l l y , the enriched rats were more disrupted by the "probe" t r i a l ( t r i a l 13) than the were normally reared rats. This could be viewed to be a res u l t of their perseveration of searching the formerly correct quadrant (quadrant 3). 46 F i g u r e 5 . L a t e n c y t o f i n d the submerged p l a t f o r m on each t r i a l f o r a l l c o n d i t i o n s . 47 100 -\ 0 — i 1 1 1 1 1 1 1 1 1 1 1 1 r -1 2 3 4 5 6 7 8 9 10 11 12 13 14 1/1 1/1 1/1 1/1 3/1 ^ 1 S3 3/3 3/3 3/3 -/3 -fl -IA -IA TRIAL CUE POSITION/PLATFORM POSITION 4 8 F i g u r e 6. L a t e n c y t o f i n d t h e submerged p l a t f o r m on e a c h t r i a l f o r a l l e n r i c h e d and n o r m a l l y r e a r e d r a t s . 4 9 TRIAL CUE POSITION/PLATFORM POSITION 50 Percentage of e n r i c h e d and normally reared r a t s t h a t contacted the cue i n the " i n c o r r e c t " quadrant on t r i a l s 7 and 8 . 51 REARING ENVIRONMENT Enr iched Normal Touched cue 29.41% 63.04% Did not touch cue 70.59% 36.96% 52 Puzzle Latch Box The latency of the rats to open the each of the three latches was analysed using a repeated-measures ANOVA. A l l three latches were learned r e l a t i v e l y quickly by a l l ra t s . An eff e c t for Latch Type (F(2,138)=64.68, p_<.01) as well as an interaction between Rearing Environment and Surgery (F(1,69)=11.37, p_<.05) and a Latch x Surgery interaction (F(2,138)=3.73, p_<.05) were found. Post-hoc comparisons (Tukey's HSD) found the enriched/dewhiskered/cauterized rats and their controls took s i g n i f i c a n t l y longer to open the door with the bolt latch than did any of the other groups (see Fi g . 7, panel B). The results for a l l three latches are summarized in Fig.7. The method of manipulation used to open the latches was e n t i r e l y dependent upon the type of latch being used and did not vary with any of the experimental factors (see Table E for summary). The snout was used predominantly for opening the b u t t e r f l y latch and the shielded b u t t e r f l y latch, while the mouth was used for the bolt la t c h . Based on these r e s u l t s , i t seems unlikely that the presence of vibrissae during development is necessary for fine manipulations of the kind measured by the puzzle latch box. Bracelet Test An analysis of variance was used to analyse each of the four measures generated from the rats' reactions to wire 5 3 F i g u r e 7. L a t e n c i e s i n seconds to open l a t c h e s . "ENRICHED" and "NORMAL" r e f e r to r e a r i n g environment; "C" and "P" r e f e r to c a u t e r i z e d s u r g i c a l procedure and plucked s u r g i c a l procedure r e s p e c t i v e l y . MEAN LATENCY (SECS) 55 Table E. Method of manipulation used to open the three latch types. A=butterfly latch; B=bolt latch; C=shielded b u t t e r f l y latch--see F i g . . Numbers represent percentage of rats using that manipulation. Snout Mouth Paws A E n r i c h e d B C a u t e r i z e d C A E n r i c h e d B C. C o n t r o l s C A E n r i c h e d B Plucked C A E n r i c h e d B P. C o n t r o l s C A Normal B C a u t e r i z e d C A Normal B C. C o n t r o l s C A Normal B Plucked C A Normal B P. C o n t r o l s C 57% 14% 29% 14% 57% 28% 71% 14% 15% 60% 20% 20% 20% 40% 40% 10 0% 0% 0% 37% 0% 62% 25% 25% 50% 100% 0% 0% 58% 8% 34% 42% 25% 33% 100% 0% 0% 90% 0% 10% 20% 40% 40% 100% 0% 0% 37% 13% 50% 35% 47% 17% 89% 0% 11% 67% 0% 33% 22% 56% 22% 100% 0% 0% 44% 11% 45% 0% 56% 44% 100% 0% 0% 57 Figure 8. Panel A: Latency to contact the wire bracelets. Panel B: Latency to remove one of the wire bracelets. "ENRICHED" and "NORMAL" refer to rearing environment; "C" and "p" refer to cauterized surgical procedure and plucked surgical procedure respectively. MEAN REMOVAL LATENCY (SECS) IS) O O o oo o o o K) o •IV o MEAN CONTACT LATENCY ( S E C S ) i • I . I . I • 59 bracelets. The four measures were: (1) latency to contact one of the wires; (2) latency to remove one of the wires; (3) the paw i n i t i a l l y contacted; (4) and the paw from which the f i r s t wire was removed. The only s i g n i f i c a n t e f f e c t found was a main eff e c t for Surgery type on the Contact Latency measure, £.(1,76)= 4.10, p_<.05. The dewhiskered cauterized rats and their controls had a s i g n i f i c a n t l y longer latency than the plucked rats and their controls (Cauterized mean=8.31 s; Plucked mean=5.44 s ) . The contact latency and removal latency data are summarized in Fig 8. Based on these data, i t appears that long-term dewhiskering plays no role in the fine motor behaviours involved in removing the wire bracelets. Snout Contact Orientation An analysis of variance was performed on the frequency of orientations across 6 t r i a l s to a l i g h t tap on the snout with a surgical swab. Long-term dewhiskering, whether by plucking or cautery, had a s i g n i f i c a n t and disruptive e f f e c t on orientation to contacts of the snout. As shown in F i g . 9, the dewhiskered rats in a l l conditions oriented s i g n i f i c a n t l y less to snout contacts than did any of the control rats (F( 1, 76 ) =36 . 48, p_<.01). No s i g n i f i c a n t interactions were observed. This e f f e c t does not appear to be due to a loss of a l l t a c t i l e c a p a b i l i t i e s ; a l l rats exhibited eye-flinch responses when tapped sharply on the snout. 60 Figure 9. Frequency of orientations to l i g h t taps on the snout with a surgical swab according to condition. "ENRICHED" and "NORMAL" refer to rearing environment; "C" and "P" refer to cauterized s u r g i c a l procedure and plucked s u r g i c a l procedure respect i v e l y . 61 0 DE WHISKERED H CONTROL C P C P ENRICHED NORMAL 62 Discuss ion One of the purposes of the present study was to examine the intermodal consequences of early, long-term somatosensory r e s t r i c t i o n and some of the factors that might eff e c t them. As mentioned previously, there are numerous theo r e t i c a l arguments (e.g. Gottlieb, 1971) to suggest that intermodal effects would be found. A related goal of the present investigation was to broadly test the motoric and perceptual effects of this early, long-term dewhiskering in rats. It was hoped that observing the effects of the manipulations of sensory experience on a battery of tests (Kolb and Whishaw, 1983) would increase our understanding of the role that the mystacial vibrissae play for rats in their interactions with their environments. Limited evidence for modality interdependence was found. Long-term dewhiskering through cauterization led to increased orientation to v i s u a l s t i m u l i . This only occurred for those animals given access to an enriched sensory environment during rearing. This finding is consistent with two hypotheses about early experience and perceptual development: 1) decreased competition during development from an early developing system (in t h i s case, the somatosensory system) leads to increased competency in a later emerging system--in t h i s case v i s i o n (Burnstine et a l , 1984; Turkewitz & Kenny, 1982); and 2) that behavioural demand is a s i g n i f i c a n t factor in the determining the impact of early somatosensory r e s t r i c t i o n on t h i s competency (Burnstine et a l , 1984). As 63 w e l l , given i n pa r t the nature of t h i s v i s u a l o r i e n t a t i o n t a sk, and the f i n d i n g t h a t animals i n a l l c o n d i t i o n s h a b i t u a t e to repeated p r e s e n t a t i o n s of the v i s u a l s t i m u l i , these data best support the c o n t e n t i o n that the compensation seen here i s p r i m a r i l y a s h i f t i n a t t e n t i o n a l r a t h e r than p r o c e s s i n g c a p a b i l i t i e s (Burnstine et a l , 1984; Tees, 1976). An i n t e r e s t i n g aspect to t h i s o b s e r v a t i o n i s t h a t no e f f e c t was found f o r the animals given access to an e n r i c h e d environment but whose v i b r i s s a e were merely plucked d u r i n g development. As mentioned p r e v i o u s l y , while t h i s procedure does not appear to d i s r u p t the c y t o a r c h i t e c t o n i c s t r u c t u r e of c o r t i c a l neurons r e l a t e d to the v i b r i s s a e r e c e p t o r s (Weller & Johnson, 1975), i t does a b o l i s h e l e c t r o p h y s i o l o g i c a l responding of these same c o r t i c a l c e l l s (Simons & Land, 1987). P a r e n t h e t i c a l l y , as data from the Snout Contact O r i e n t a t i o n task i n the present study i n d i c a t e , long-term p l u c k i n g does attenuate o r i e n t a t i o n to t a c t i l e cues p r o v i d i n g b e h a v i o u r a l evidence that t h i s m a nipulation does have some s p e c i f i c intramodal consequences. However, i t appears from the r e s u l t s of the v i s u a l o r i e n t a t i o n task t h a t even though the c o r t i c a l u n i t s corresponding to the v i b r i s s a e are presumably unresponsive, they are s t i l l p r o v i d i n g some kind of intermodal i n f l u e n c e with r e s p e c t to the v i s u a l system. There are some d i f f e r e n c e s between the r e s u l t s of the study and those found i n previous work us i n g t h i s v i s u a l o r i e n t a t i o n paradigm (e.g. Midgley & Tees, 1983). In prev i o u s s t u d i e s , s i g n i f i c a n t d i s h a b i t u a t i o n was observed i n normal l i g h t - r e a r e d animals with the s h i f t from the s o l i d 64 display to the rapi d l y flashing display on t r i a l 11. In the present study, no r e l i a b l e dishabituation was observed on t r i a l s 11-20. This is most l i k e l y attributable to the differences in intensity of the l i g h t displays used in the past and in the present experiment. The illuminance of the LEDs in the display used in the present study was 4.8 cd/m2, whereas in the previous work, the l i g h t displays have been somewhat brighter--5.25 cd/m2 (Midgley & Tees, 1983). As indicated by Midgley and Tees (1983), l i g h t i n t e n s i t y of displays can be a s i g n i f i c a n t factor in determining rates of habituation and dishabituation. The less intense displays used in the present study most l i k e l y rendered the s h i f t s from display to display less s a l i e n t than in early reports (e.g. Midgley & Tees, 1983), thus making dishabituation to s h i f t s in the stimuli less l i k e l y . Performance on the water maze was used to examine a second proposal of Turkewitz & Kenny, (1982). Their "organizational framework" proposal stated that i f experience related to an e a r l i e r developing system is necessary to establish a framework for a behaviour, that is then assimilated by later developing systems, then a reduction in competency related to the later developing system would be expected. In s p a t i a l behaviour as assessed by the present version of the water maze, early t a c t i l e r e s t r i c t i o n had no e f f e c t on performance. This res u l t can be interpreted in a number of d i f f e r e n t ways. F i r s t , i t may be that t a c t i l e input is unnecessary for normal s p a t i a l behavior. Many authors have suggested that v i s u a l input is of primary 65 importance for appropriate s p a t i a l behaviour (Burnstine et a l , 1984; Gibson, 1969; Tees et a l , 1981). Thus i t may be that the "organizational framework" for s p a t i a l behaviour i s for the most part dependent on appropriate v i s u a l c a p a b i l i t i e s ; t a c t i l e r e s t r i c t i o n is of no consequence to s p a t i a l behaviours. There is some evidence to support th i s hypothesis (e.g. Tees et a l , 1981). A second p o s s i b i l i t y is that since tactual cues or signals are not necessary to solve the water maze problem, t a c t i l e r e s t r i c t i o n might be of no consequence. Early reports (Bogardus & Henke, 1911) espoused the necessity for normal t a c t i l e input in appropriate s p a t i a l behaviours in rats . Bogardus and Henke (1911) examined acutely dewhiskered animals in an alley-way type maze. Thus, i t may be that, in a s p a t i a l task that incorporated some potential l o c a l t a c t i l e cues (e.g. Hebb-Williams maze or r a d i a l arm maze), d i f f e r e n t r e s u l t s might have been found for the long-term dewhiskered animals. A f i n a l p o s s i b i l i t y is that the water maze is too simple a task for the p o t e n t i a l l y subtle differences that dewhiskering might be causing. This p o s s i b i l i t y seems unli k e l y given the differences found with respect to enrichment. This e f f e c t of early rearing environment on water maze performance was to be expected, given the superior performance of enriched animals in other s p a t i a l tasks (e.g. Greenough & Juraska, 1979; Juraska et a l , 1984). However, a number of interesting results emerged form the use of the version of the water maze task employed in the present study. 66 S p e c i f i c a l l y , the mani p u l a t i o n of the l o c a l v i s u a l cue i n the present study had s i g n i f i c a n t e f f e c t s f o r the behaviour of the normally r e a r e d animals. F i r s t , the normally reared animals were s i g n i f i c a n t l y poorer than t h e i r e n r i c h e d c o u n t e r p a r t s at f i n d i n g the p l a t f o r m on the f i r s t t r i a l . T h i s may be a r e s u l t of l e s s a t t e n t i o n being paid by the normally reared animals to the presence of the l o c a l v i s u a l cue. Neither the submerged p l a t f o r m nor the cue was present d u r i n g the p r e - t r i a l h a b i t u a t i o n phase of the study, thus the cue r e p r e s e n t s a novel v i s u a l stimulus on the f i r s t t r i a l . I t may be t h a t the en r i c h e d r a t s were more a t t e n t i v e to the presence of the cue. Another p o s s i b i l i t y i s t h a t the enr i c h e d r a t s were j u s t more l i k e l y to explore or approach the cue; the normally reared animals may a l s o have seen the cue but may have p r e f e r r e d to s c r a b b l e a g a i n s t the w a l l of the p o o l . Previous r e s e a r c h has shown t h a t animals reared i n e n r i c h e d environments tend to be more l i k e l y to explore u n f a m i l i a r o b j e c t s (Renner, 1987). The normally reared animals were d i s r u p t e d by the s h i f t of the l o c a l cue on t r i a l 5 and by i t s movement to the quadrant with the p l a t f o r m on t r i a l 7 and 8. From these f i n d i n g s , i t appears that the normally reared animals were l e s s a t t e n t i v e to the a v a i l a b l e d i s t a l cues i n the t e s t i n g room than the enr i c h e d animals. The normally reared animals seemed to be r e l y i n g on the (presumably) more s a l i e n t proximal v i s u a l cue ( i . e . the r a c q u e t - b a l l ) than the enr i c h e d animals. The d i f f e r e n t i a l performance on the "probe" t r i a l ( t r i a l 67 13) of the animals reared in the two environments provides support for the interpretation that the normally reared animals showed decreased attentiveness to d i s t a l cues. The enriched animals were more disrupted by the s h i f t i n g of the platform to a novel quadrant than the control animals. This appears to be a res u l t of the enriched animals being more l i k e l y to perseverate in searching the previously correct quadrant. It may be that the normally reared animals are less l i k e l y to perseverate in using d i s t a l cues i f they don't find the platform and thus switch to a general maze searching strategy e a r l i e r than the enriched animals. The results of the v i s u a l orientation task and the water maze provide limited but important evidence of intermodal effects due to long-term t a c t i l e r e s t r i c t i o n . T a c t i l e r e s t r i c t i o n in combination with access to an enriched environment lead to changes in orientation to repeated v i s u a l stimuli but had no e f f e c t on s p a t i a l behaviour. Thus, the present investigation provides support for the f i r s t proposition of Turkewitz & Kenny (1982)--that decreased competition from an early developing system leads to increased competency in a later developing system. However, the present study does not support the "organizational framework" hypothesis of Turkewitz & Kenny (1982). Early t a c t i l e r e s t r i c t i o n played no role in s p a t i a l competency, at least in the test used in the present study. The remaining three tasks (Puzzle Latch Box, Wrist Bracelet Task, and Snout Contact Orientation) were primarily used as assessments of the intramodal effects of long-term 68 dewhiskering. The results of the Puzzle Latch Box test indicate that fine manipulaitons of the type necessary for th i s task do not require the presence of vibrissae during development. The absence of vibrissae appeared to be of no consequence even in cases (e.g. the shielded b u t t e r f l y latch) where snout use was predominant (see Table E and Figure 7). However, in most cases, the top of the snout was used to open a l l the latches, thus i t may be that these latch types were not s u f f i c i e n t l y challenging to reveal differences due to dewhiskering. Another p o s s i b i l i t y is that the dewhiskered animals had switched to the use of v i s u a l cues to guide their behaviour. This seems unlikely, however, since, for rats, v i s u a l cues within 7 cm of their eyes are not in focus (Powers & Green, 1978), and a l l manipulations occurred at considerably less distance from the rats' eyes. Dewhiskering also played no s i g n i f i c a n t role in performance on the Wrist Bracelet task. Since the primary method of removal was by chewing the wire, i t seems un l i k e l y that vibrissae play an important role in manipulations involving the mouth area. Also, the lack of difference between dewhiskered and control animals in contacting the wire bracelets indicates that there is l i k e l y no s i g n i f i c a n t change in t a c t i l e sensation in the paw area due to long-term dewhiskering. Interestingly, no effects were observed with respect to any of the experimental factors in terms of side of f i r s t contact or side of f i r s t removal. If one assumes thi s test as a measure of l a t e r a l i t y as expressed by 69 pawedness, then s t i m u l a t i o n h i s t o r y appears to p l a y l i t t l e r o l e i n the development of population-based l a t e r a l i t y i n r a t s . T h i s idea i s not c o n s i s t e n t with the hypothesis of Denenberg (1981) t h a t exposure to e n r i c h e d environments d u r i n g r e a r i n g should i n c r e a s e l a t e r a l i t y i n r a t s , s t r e n g t h e n i n g the c o n t r o l of many behaviours i n the r i g h t hemisphere. T h i s presumably, would lead to an i n c r e a s e d i n c i d e n c e i n population-based left-pawedness. The present study does not support t h i s h y p o t h e s i s . F i r s t , the e n r i c h e d animals showed no s i g n i f i c a n t paw p r e f e r e n c e , n e i t h e r i n f i r s t c o n t a c t nor f i r s t removal. Secondly, long-term t a c t i l e r e s t r i c t i o n d i d not e f f e c t paw preference f o r e i t h e r of the measures i n the present study. T h i s i s c o n s i s t e n t with previous r e p o r t s (e.g. Tees, 1984) which i n d i c a t e t h a t l i m i t i n g e a r l y v i s u a l s t i m u l a t i o n had no e f f e c t on s e v e r a l measures of l a t e r a l i t y . The r e s u l t s of the Snout Contact O r i e n t a t i o n Test i n d i c a t e t h a t the presence of v i b r i s s a e d u r i n g development appear to be important f o r normal o r i e n t a t i o n to t a c t i l e s t i m u l i . T h i s i s true both f o r animals with r e c e p t o r d e s t r u c t i o n (the c a u t e r i z e d animals) and those t h a t had been plucked. T h i s i s i n accordance with the f i n d i n g s of Simons & Land (1987) t h a t long-term t a c t i l e r e s t r i c t i o n (by shaving) a b o l i s h e s responding of c o r t i c a l v i b r i s s a e r e c e p t o r c e l l s ; d e s t r u c t i o n of the p e r i p h e r a l r e c e p t o r s i s not necessary f o r f u n c t i o n a l d i s r u p t i o n of t h i s system. The r e s u l t s of the f i n a l three tasks i n d i c a t e t h a t v i b r i s s a e p l a y l i t t l e r o l e i n f i n e manipulations i n v o l v i n g 70 the mouth, snout or paws, but are very important in terms of orientation to t a c t i l e contact. Since vibrissae a c t i v i t y ( i . e . whisking) increases during exploration in rats (Woolsey and Van Der Loos, 1970) i t appears l i k e l y that they play a s i g n i f i c a n t role in exploration and orientation to t a c t i l e s t i m u l i . Given the rats' nocturnal l i f e s t y l e and i t s poor short-range ( i . e . less that 7 cm) v i s u a l capacities (Powers & Green, 1978), i t may be that the vibrissae are used to orient the animal to objects for further olfactory or gustatory invest igat ion. A comment should be made about the effects fo the cauterizing procedure on the behaviour of rats . In the case of the Latch Puzzle Box and the Bracelet task, i t was found that the cauterizing procedure s i g n i f i c a n t l y disrupted performance. This diminished competency might be due to an increase in the emotionality of the cauterized animals due to the r e l a t i v e l y traumatic e f f e c t of the surgical procedure. Previous reports (Keramidas, 1976; Vincent, 1912) have indicated that vibrissae removal leads to increased emotionality. Although this alternative explatnation might be plausible with respect to the results obtained by the enriched/dewhiskered/cauterized animals in the vi s u a l orientation task, t h i s seems unlikel y given that the normally reared/dewhishered/cauterized animals did not respond in a similar fashion. 71 Conclus ions Gibson (1969) d e s c r i b e s the case of a young boy i n Boston who has been b l i n d s i n c e b i r t h . Although b l i n d , t h i s boy i s capable of r i d i n g h i s bike through the s t r e e t s of Boston without much d i f f i c u l t y . The boy a p p a r e n t l y uses a u d i t o r y cues not only to navigate throughout the c i t y but a l s o , presumably, to avoid v a r i o u s o b s t a c l e s . An intermodal consequence of e a r l y v i s u a l d e p r i v a t i o n has presumably occurred; the boy has presumably compensated through i n c r e a s e d a t t e n t i o n to n o n - v i s u a l cues. While, intermodal compensation a f t e r unimodal r e s t r i c t i o n i s the most commonly c i t e d form of mo d a l i t y interdepence (Burnstine i t a l , 1984), i t i s not the onl y form. M o d a l i t y interdependence can a l s o be s a i d to occur i f unimodal d e p r i v a t i o n changes performance on a task i n which s i g n a l s i n v o l v i n g many m o d a l i t i e s may be p a r t i c i p a t i n g (e.g. s p a t i a l b e h a v i o u r ) . As w e l l , i f competency i n one modality f o r a behaviour i s based on the i n t e g r i t y of an " o r g a n i z a t i o n a l framework" f o r another modality, then m o d a l i t y interdependece should be demonstrable a f t e r d i s r u p t i o n of t h a t framework by evidence of reduced competency. The present study examined both of these p r o p o s i t i o n s concerning modality interdependence. In accordance with past b e h a v i o u r a l (e.g. Keramidas, 1976; Turkewitz et a l , 1982) and neuroanatomical (e.g. Ryugo et a l , 1975) evidence, i t was 72 found that long-term t a c t i l e r e s t r i c t i o n (through dewhiskering) had s i g n i f i c a n t e f f e c t s f o r the development of other m o d a l i t i e s . Thus, i n the examination of the r o l e of experience i n the development of p e r c e p t u a l competency, a broad view of the kinds of experience t h a t might be a f f e c t i n g s p e c i f i c competencies must be adopted by developmental p s y c h o b i o l o g i s t s i n t e r e s t i n the r o l e of experience. Examining the e f f e c t s of unimodal d e p r i v a t i o n on the development of t h a t modality i s not s u f f i c i e n t f o r a complete account of the r o l e experience p l a y s i n development. As w e l l , as the present study demonstrates, the use of s e v e r a l d i f f e r e n t tasks to assess the b e h a v i o u r a l consequences of a m a n i p u l a t i o n can y i e l d more i n t e r p r e t a b l e f i n d i n g s than the use of a s i n g l e task. In the present examination, a b a t t e r y of t e s t s s p e c i f i e d which behaviours are most a f f e c t e d by changes i n s t i m u l a t i o n h i s t o r y , b e t t e r i l l u m i n a t i n g the r o l e played by experience i n the normal development of v i b r i s s a e - e n v i r o n m e n t a l i n t e r a c t i o n s of the r a t . The present study, however, i s by no means an exhaustive examination; a number of i s s u e s s t i l l remain to be e x p l o r e d . For i n s t a n c e , the e f f e c t of long-term somatosensory r e s t r i c t i o n on complex s o c i a l i n t e r a c t i o n s might be explored u s i n g a paradigm s i m i l a r to Whishaw and Tomie (1988), wherein the motor p a t t e r n s of food s t e a l i n g and dodging from i n t r u d e r s are examined. As w e l l , other s p e c i e s - s p e c i f i c behaviours such as the d e f e n s i v e burying of dangerous o b j e c t s (e.g. P i n e l and T r e i t , 1978) might be examined to b e t t e r 73 c l a r i f y the r o l e v i b r i s s a e p l a y i n other complex motor behaviours. F i n a l l y , i t might be i n t e r e s t i n g to examine the e f f e c t s of e a r l y v i b r i s s e c t o m y on the p a t t e r n s of emergence of behaviours mediated by other sensory systems. Kenny and Turkewitz (1986) found an i n t e r e s t i n g s h i f t i n the e a r l y development of homing behaviour of r a t s due to premature e y e l i d opening. Moreover, Moye and Rudy (1985) found that r a t s e a r l y i n development e x h i b i t r e f l e x r e a c t i o n s to v i s u a l s t i m u l i before they are capable of forming c o n d i t i o n e d a s s o c i a t i o n s to these s t i m u l i . One might examine the e f f e c t of e a r l y somatosensory r e s t r i c t i o n on the emergence of behaviours of t h i s nature. The presence of the m y s t a c i a l v i b r i s s a e d u r i n g ontogeny are important to the r a t not o n l y i n terms of normal somatosensory p e r c e p t i o n and development but a l s o i n terms of the emergence of competencies r e l a t e d to other p e r c e p t u a l systems. While s t o r i e s of b l i n d , b i k e - r i d i n g boys are b o u n t i f u l , the present study c o n t r i b u t e s to a growing but s t i l l l i m i t e d body of l a b o r a t o r y evidence f o r modality interdependence . 7 4 REFERENCES Belford, G.R., & Killackey, H.P. (1979). 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