Removal of two halves restores the whole: reversal of visual hemineglect during bilateral cortical or collicular inactivation in the cat.

The purpose of the present study was to compare visual orienting behavior in the adult cat during (1) unilateral and bilateral cooling deactivation of posterior-middle suprasylvian (pMS) sulcal cortex, and (2) unilateral and bilateral deactivation of the superior colliculus. As expected, unilateral cooling deactivation of either pMS cortex or the superior colliculus resulted in a profound visual neglect of the contracooled hemifield. The addition of cooling the homotopic region in the opposite hemisphere largely reversed this deficit and restored visual orienting into the previously neglected hemifield. These results show that (1) pMS cortex and the superior colliculus are essential for normal detection and orienting to visual targets, and (2) unilateral visual neglect results from an imbalance of activities in the two hemispheres induced at either cortical or subcortical levels. These conclusions have implications for understanding neural bases of visual hemineglect following unilateral lesions in humans.