Visual localization and discrimination after ibotenic lesion of the cat orbito-insular cortex

Behavioral tasks were used to investigate how the orbito-insular cortex (OIC) of the cat is involved in complex operations such as the orienting reaction towards a novel stimulus. Six cats were trained preoperatively on a perimetry test to assess their ability to orient the head and eyes to objects presented in restricted regions of the visual field, and on brightness, pattern and form discrimination tasks for food reward in a two-choice discrimination apparatus. Two animals then underwent unilateral chemical lesion of the OIC using injections of ibotenic acid, two others received bilateral lesions of this same area, and the remaining two cats were used as normal controls. Postoperative performance of brightness, pattern and form discrimination was normal following OIC lesions, and no lack of retention was observed. In contrast, the cats with OIC lesions had significant deficits in their visually guided behavior. The cats ignored objects presented in the monocular segment of both sides of the visual field, even after unilateral lesion, and there was an effect on the ability to attend and fixate the central preconditioned stimulus.