IMPAIRMENT OF VISUAL OBJECT-DISCRIMINATION LEARNING AFTER PERIRHINAL CORTEX ABLATION

Eight cynomolgus monkeys learned preoperatively 20 concurrent visual d iscriminations between pairs of colored shapes presented on a touch sc reen with 24-hr intertrial intervals. Three then received bilateral pe rirhinal cortex ablation, and 5 remained controls. The ablated monkeys were severely impaired in reacquiring the preoperatively acquired set , whereas postoperative learning of 20 new discriminations was not sig nificantly affected. The task was then made more difficult. First, the number of foils from which the stimulus had to be selected was increa sed to 2, 4, 7, and then 14. Second, larger sets of 40, 80, and 160 pr oblems were presented. Both manipulations revealed some significant bu t relatively mild impairments in the monkeys with ablations. It is sug gested that perirhinal cortex ablation impairs the monkey's capacity t o identify individual objects, which leads to deficits in both visual- object recognition memory and discrimination learning.