Journal of Neuroscience, Vol 14, 2128-2139, Copyright © 1994 by Society for Neuroscience
Effects of selective neonatal temporal lobe lesions on visual recognition memory in rhesus monkeys
J Bachevalier and M Mishkin
Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, Maryland.
Ten-month-old infant monkeys that had received neonatal ablations of either
inferior temporal cortex (area TE) or the medial temporal region were
compared with age-matched normal infant monkeys in visual delayed
nonmatching-to-sample with trial-unique objects. Both types of early damage
caused impairment in visual recognition, but the degree of deficit after
early area TE lesions differed sharply from that after early medial
temporal removals. Thus, whereas early medial temporal damage yielded a
marked decline in visual recognition when the delays and lists were
gradually increased, early area TE damage yielded normal recognition up to
a delay of 60 sec and only mild impairment at longer delays and lists. The
data indicate that, unlike adult monkeys, which suffer severe and nearly
equivalent losses in visual object recognition after both types of
ablation, the infant monkeys' recognition ability is largely spared after
early damage to area TE but not after early damage to the medial temporal
lobe. Together with recent clinical reports of profound memory loss in
children with early dysfunction of the medial temporal region, the present
findings demonstrate that medial temporal lobe structures operate early to
sustain visual recognition memory, and recovery from early damage is
limited at best. Early damage to higher-order visual cortex, however, can
be largely compensated, presumably by one or more of the visual cortical
areas that were left intact.