LONG-TERM EFFECTS OF SELECTIVE NEONATAL TEMPORAL-LOBE LESIONS ON LEARNING AND MEMORY IN MONKEYS

Rhesus monkeys with neonatal damage to either the medial temporal lobe or the inferior temporal cortical area TE, and their normal controls, were reassessed in visual habit formation (24-hour intertrial interva l task) and visual recognition (delayed nonmatching to sample; DNMS) a t 4-5 years of age and then tested on tactile and spatial DNMS. Result s on the two visual tasks were the same as those obtained when the mon keys were under 1 year of age. Specifically, early medial temporal les ions, like late lesions, left habit formation intact but severely impa ired recognition memory. Furthermore, the memory deficit extended to t he tactile and spatial modalities. By contrast, early damage to TE, un like late damage to it, yielded only mild deficits on both visual task s and had no effect on tactile or spatial DNMS. Compensatory mechanism s that promote substantial and permanent recovery thus appear to be av ailable after neonatal TE lesions but not after neonatal medial tempor al lesions.