Role of inferior temporal cortex in interhemispheric transfer.

Neurons in inferior temporal cortex of the rhesus monkey usually have large receptive fields that extend well across the midline into both visual half-fields. The responsiveness of these neurons to stimuli in the ipsilateral visual half-field depends on the splenium and anterior commissure, the same pathways necessary for interhemispheric transfer of visual habits. Since inferior temporal neurons have the same trigger features in both half-fields and are usually binocular, they may be the site of the interhemispheric neural convergence that underlies interhemispheric transfer. If so, bilateral removal of inferior temporal cortex should interfere with interhemispheric transfer even when the commissures are intact. To test this, monkeys were trained on pattern discriminations with one eye and then tested for transfer with the other eye. Five experimental monkeys received bilateral inferior temporal lesions and, to restrict input from each eye to one hemisphere, section of the optic chiasm. Ten controls received either bilateral temporal lesions alone, chiasm section alone or remained unoperated. Only the experimental animals showed impaired transfer. These results suggest that inferior temporal neurons mediate interhemispheric transfer by providing perceptual equivalence for patterns in the left and right visual fields, and, by implication, perhaps also for patterns in different parts of the same field.