Dissociation of the effects of inferior temporal and limbic lesions on object discrimination learning with 24-h intertrial intervals.

Monkeys with bilateral ablations of the inferior temporal cortical area TE were trained on a visual discrimination task thought to measure non-cognitive habit formation. The task consisted of 20 object discriminations presented concurrently, but at the rate of only one trial on each per day; successive trials on a given discrimination were thus separated by 24-h intertrial intervals. Performance on this task by the animals with TE lesions was compared to that of both normal control monkeys and monkeys that had sustained bilateral removals of the amygdala and hippocampus. In contrast to the latter animals, which learned the 24-h intertrial interval task about as quickly as the normal controls, monkeys with area TE removals were markedly impaired. Taken together with earlier findings demonstrating that ablation of area TE impairs visual recognition memory, the present results suggest that area TE contributes not only, like limbic structures, to a cognitive memory system, but also, unlike limbic structures, to a non-cognitive habit system. Evidence is reviewed suggesting that this latter system may involve a corticostriatal circuit.