Role of the hippocampus plus subjacent cortex but not amygdala in visuomotor conditional learning in rhesus monkeys

Rhesus monkeys were trained to learn a large series of visuomotor conditional associations, each involving the arbitrary coupling of a visual stimulus with 1 of 3 potentially correct forelimb movements. The monkeys then received bilateral aspiration lesions of either the amygdala plus subjacent cortex or the hippocampus plus subjacent cortex. Hippocampal but not amygdala removals significantly retarded the learning of new visuomotor associations. Neither lesion affected retention. The findings argue against a general role for the amygdala in associating information across modalities, construed broadly to include motor information. By contrast, the finding that the hippocampal formation and its subjacent cortex play a role in learning new sensorimotor associations supports the view that this region participates in the long-term storage of associative information or in the recall of recently acquired information.