Journal of Neuroscience, Vol 2, 1214-1220, Copyright © 1982 by Society for Neuroscience
Hippocampal resections impair associative learning and recognition memory in the monkey
H Mahut, S Zola-Morgan and M Moss
Damage to the hippocampus has been implicated in the permanent loss of
memory in patients with medial temporal lobe resections. In two previous
studies, it was established that bilateral ablations of the hippocampus in
the monkey impaired performance on an associative learning task and on an
object discrimination retention task. The two objectives of the present
study were to assess the long term effects of hippocampal resections in the
monkey and to extend the analysis of the effects of these resections to
recognition memory. Therefore, the performance of monkeys with either
hippocampal ablations or fornix transections, sustained 5 years earlier,
was compared (1) on a concurrent discrimination task--a previously
unencountered associative learning task--and (2) on a nonmatching-to-sample
recognition task with either delays interposed between the presentation of
the sample object and the recognition trial or with lists of either 1-, 3-,
5-, or 10- object samples. Significant impairment on both tasks was found
after hippocampal, but not after fornix, damage. Though monkeys in the
hippocampal group were impaired on both delays and lists, the impairment
was more severe on the lists, with abnormal sensitivity to pro- and
retroactive interference as a possible source of difficulty. Thus, in
parallel with clinical findings, ablations of the hippocampus in the
nonhuman primate produce an enduring disruption of memory.
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