Visual recognition in monkeys: effects of transection of fornix.

An earlier finding from this laboratory of only a mild recognition impairment after hippocampal removal in mature monkeys (Mishkin 1978) contrasts with the severe deficit originally reported by Gaffan (1974) following transection of the fornix in immature monkeys. Investigation of some of the methodological differences between the two studies (lesion site, age of monkeys, and behavioral paradigm) failed to resolve the discrepancy in results, only a small impairment resulting under all conditions examined. While some still unexplored differences must underlie the divergent findings, it appears that only a comparatively mild impairment in recognition memory results from damage to the hippocampal system under a wide variety of conditions.