Contributions of the corpus callosum and the anterior commissure to visual activation of inferior temporal neurons

Most neurons in the inferior temporal cortex of the rhesus monkey have visual receptive fields that extend across the vertical meridian well into both the contralateral and ipsilateral visual half-fields. We examined the role of different portions of the forebrain commissures in providing the ipsilateral input with the following results. (1) Combined section of the splenium and anterior commissure eliminated visual activation from the ipsilateral visual half-field. (2) Section of the splenium, with sparing of the anterior commissure, reduced the incidence of ipsilateral activation by about one-half. (3) Section of the anterior commissure, with sparing of the splenium, did not alter the incidence of ipsilateral activation. (4) Section of the non-splenial portions of the corpus callosum had no effect on the laterality of the receptive fields. Thus, both the splenium and the anterior commissure but not the non-splenial callosum can provide information from the ipsilateral visual field to neurons in inferior temporal cortex. These results are interpreted as suggesting that the converging input from the two visual half-fields onto single inferior temporal neurons provided by the forebrain commissures may mediate interhemispheric transfer of visual habits.