Visual agnosia and Kluver-Bucy syndrome in marmosets (Callithrix jacchus) following ablation of inferotemporal cortex, with additional mnemonic effects of immunotoxic lesions of cholinergic projections to medial temporal areas

Inferotemporal ablations in the New World monkey, the common marmoset (Call ithrix jacchus), produced a persistent impairment on visual discrimination learning and a florid, but transient, Kluver-Bucy syndrome. Monkeys with th ese ablations were impaired on acquisition of object discriminations to a h igh criterion and on concurrent discrimination learning, to a single high c riterion across all trials. Neither the control monkeys nor the monkeys wit h inferotemporal ablations found acquisition more difficult when the compon ent discriminations of a set were presented concurrently compared to consec utively, although the monkeys with inferotemporal ablations found acquisiti on under both these conditions somewhat more difficult than did control mon keys. This suggests that the severe impairment caused by inferotemporal abl ations on concurrent learning measured across all trials is due to the need for sustained performance across a concurrent set rather than to the extra mnemonic demands of concurrent presentation. When immunotoxic lesions of t he cholinergic projection to the hippocampal formation were added to the in ferotemporal ablations. a further impairment on retention, and a differenti al impairment on concurrent, compared to consecutive, learning was observed . Previous studies have shown that lesions of the cholinergic projection to the hippocampus alone, or excitotoxic hippocampal lesions, do not affect s imple visual discrimination learning. It is suggested that large inferotemp oral ablations in monkeys produce a visual agnosia which causes severe 'psy chic blindness' in the first instance, and a persistent impairment on visua l discrimination learning. The hippocampus makes a contribution, which may be mnemonic, to discrimination performance after inferotemporal ablations. (C) 2001 Elsevier Science B.V. All rights reserved.