Visual discrimination performance following partial ablations of the temporal lobe: I. Ventral vs. lateral.

Abstract

Recent investigation has demonstrated that extensive bilateral ablation of the temporal lobes of monkeys produces marked impairment, independent of field defects, in their performance on visual tasks. To determine whether damage to a particular portion of the temporal lobe is implicated in such behavioral changes, 2 baboons (Papio papio, Papio porcarius) were prepared with temporal lobectomies, 2 with lateral surface ablations, and 4 with ventral surface-hippocampal ablations. One animal from each operate group was tested for postoperative retention, the others for initial postoperative learning, on a series of visual discriminations. All animals received, in addition, the delayed-response test, visual field and acuity tests, and tests of reactions to familiar objects. Following the behavioral observations the animals were sacrificed and the lesions verified. Analysis of the behavioral results showed that ventral-hippocampal ablation, as well as lobectomy, in contrast to lateral resection (or any form of unilateral lesion) produced marked impairment in visual discrimination performance. Deficits occurred more frequently in initial learning than in retention and appeared to be related to test difficulty, confounded with order. With the exception of the lobectomized animals'' increase in approach responses to inedible and previously aversive objects, no consistent postoperative effects were obtained with any of the other tests.