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A behavioural examination of the intramodal and intemodal consequences of long-term tactile restriction by vibrissae removal in rats Symons, Lawrence André


Despite the extensive work done on the neural consequences of tactile restriction very little is known about the behavioural consequences of this manipulation. In the present investigation, an assessment was made of the effects of early, long-term tactile restriction by bilateral removal of the mystacial vibrissae on the subsequent somatosensory capacities of rats (i.e. the intramodal consequences) as well as its effects on visual and spatial capacities (i.e. the intermodal consequences). As well, rearing environment (enriched vs. normal) and type of surgery (vibrissae removal by cauterization of follicles or by plucking) were examined to determine specific factors that might influence the effect of early, long-term vibrissae removal. Five tasks were used to assess these effects. The first two tasks assessed the intermodal consequences of vibrissae removal. Visual competence was assessed by measuring the habituation of orientation to repeated visual stimuli and the dishabituation to subtle changes in these stimuli. A version of the Morris (1981) water maze was used to assess the rats' spatial abilities. The results of these two tasks revealed limited evidence for intermodal effects. In terms of habituation to visual orientation, rats that had had their vibrissae removed by cauterization and were subsequently reared with daily access to an enriched environment required more trials to habituate to the presentation of repeated visual stimuli. As well, these rats were the only group to dishabituate to a subtle change in the stimuli. No effect of vibrissae removal was found in the spatial task, and environmental enrichment during development enhanced performance on this task, apparently through increased attention to distal cues by rats reared in this condition. The remaining three tasks assessed the motoric and somatosensory effects of tactile restriction. No effect 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 significant effect was observed in reactions to the tying of pieces of wire to the rats' wrists. However, early, long-term vibrissae removal (by cauterization of follicles or by plucking) attenuated orientation to contacts of the mystacial pad itself. This effect was dissociated from tactile reactivity; all rats exhibited eye-flinch responses to taps on this area. These results suggest that early, long-term tactile restriction has significant behavioural consequences for the somatosensory system as well as the visual system. These data also provide limited evidence for theories of modality interdependence as well as yielding basic information concerning the role of the mystacial vibrisse in the behaviour of the rat.

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