Effects of unilateral and bilateral lesions of the lateral suprasylvian area on learning and interhemispheric transfer of pattern discrimination in the cat.

The aim of the present experiment was to evaluate the hypothesis that the lateral suprasylvian area is involved in the interhemispheric transfer of visual information. This area was surgically removed in 10 cats which had previously undergone a midsagittal transection of their optic chiasmas. The animals then learned a pattern discrimination using either one or the other hemisphere and were tested for transfer using the other, untrained hemisphere. The lateral suprasylvian area in the intact hemisphere was next ablated in 6 of these cats. Each hemisphere was trained on a new pattern discrimination and tested for transfer using the other. The results obtained with the unilaterally lesioned animals indicated that: (a) learning with the lesioned hemisphere was as rapid as with the intact hemisphere; and (b) that transfer in either direction was normal although slightly retarded, but not significantly so, when the information proceeded from the intact to the lesioned hemisphere. Learning with either hemisphere of the bilaterally lesioned animals also appeared to be normal. Learning with the hemisphere which was lesioned second and transferring to the one which was ablated first was within normal range whereas transfer was generally not as immediate when the procedure was reversed. As a whole, the results, when coupled with those of others, would tend to indicate that the lateral suprasylvian area is involved in interhemispheric transfer but shares this function with other callosally connected areas of the primary visual cortex.