Developmental study of the hippocampal formation in rhesus monkeys (Macaca mulatta): II. Early ablations do not spare...

A companion article (see record 2005-06959-001) revealed that hippocampectomy in infancy spares concurrent discrimination learning but not recognition memory. The present report describes the results obtained with a more complex task, conditional object- object association, in which rhesus monkeys (Macaca mulatta) had to first learn to discriminate between pairs of objects rather than single ones and to subsequently remember which particular object had been a member of a rewarded stimulus pair (contextual retrieval). Hippocampectomized infants obtained normal scores in learning individual pair discriminations, but they were severely impaired in contextual retrieval. The results are interpreted in terms of a dual-system theory proposed by R. Hirsh (1974). The results point out not only the importance of age at testing but also the nature of the task. The authors were also able to glimpse possible instances of cooperation or competition between the 2 systems.