Hippocampal damage in adult humans impairs episodic and semantic memory, whereas hippocampal damage early in life impairs episodic memory but leaves semantic learning relatively preserved. We have previously shown a similar behavioral dissociation in nonhuman primates. Hippocampal lesions in adult monkeys prevents allocentric spatial relational learning, whereas spatial learning persists following neonatal lesions. Our current investigations aim to describe the neuroanatomical changes that occur in the monkey medial temporal lobe following neonatal selective hippocampal lesions.
In a first study, our results suggest that the caudal perirhinal cortex, the parahippocampal cortex and the retrosplenial cortex may contribute to spatial learning in the absence of functional hippocampal circuits, whereas the caudal entorhinal cortex may require hippocampal output to support spatial learning. We are currently investigating the effects of these neonatal selective hippocampal lesions on other medial temporal lobe structures.