A comparison of lateral peristriate and striate neocortical ablations in the rat

The effects of striate, lateral peristriate and sham ablations upon the post-operative reacquisition of visual discriminations were studied in two experiments. The results of Experiment 1 indicated that lesions restricted to the lateral peristriate neocortex rendered the rat incapable of resolving an oblique stripe discrimination. Seven of the 9 rats with striate ablations were unable to form the discrimination. The histological findings indicated that the deficit following lateral peristriate injury was not due to interruption of the geniculostriate system. However, the behavioral impairment in destriate rats corresponded to the degree of unintentional injury in lateral peristriate neocortex, but not medial peristriate tissue. In Experiment 2, the effects of these lesions were studied upon the post-operative reacquisition of either a non-reversal or reversal of a preoperatively acquired brightness discrimination. Animals with striate damage demonstrated considerable savings on the non-reversed brightness discrimination, and they acquired the reversal at a rate equal to that seen in animals with sham ablations. Rats with peristriate ablations showed no savings on the non-reversed brightness habit, and they required more extensive training than both the striate and sham groups on the reversal. These findings suggest that the frequently reported loss of a preoperative brightness habit following large posterior neocortex ablations is due to damage in the lateral peristriate neocortex rather than damage of the geniculostriate system. These results, taken with other literature, suggest an important role of the lateral peristriate neocortex in visuospatial sensory function.