Long-term effects of neonatal damage to the hippocampal formation and amygdaloid complex on object discrimination and object recognition in rhesus monkeys (Macaca mulatta)

Rhesus monkeys with neonatal aspiration lesions of the hippocampal formatio n or the amygdaloid complex were tested on concurrent discrimination learni ng (24-hr intertrial interval [ITI]) at 3 months, on object recognition mem ory (delayed nonmatching-to-sample [DNMS]) at 10 months, and retested on bo th tasks at 6-7 years of age. Neonatal amygdaloid damage mildly impaired ac quisition at the 24-hr ITI and the performance test of DNMS at both ages. I n contrast, early hippocampal lesions impaired performance only on the long est lists of 10 items in DNMS in adult monkeys. Thus, early amygdala lesion s appeared to have resulted in a greater object memory loss than early hipp ocampal lesions. However, in light of recent findings from lesion studies i n adult monkeys, the object memory impairment after early amygdaloid lesion s is better accounted for by damage to the entorhinal and perirhinal cortex than by damage to the amygdaloid nuclei.