Memory in monkeys severely impaired by combined but not by separate removal of amygdala and hippocampus

Abstract

THE profound anterograde amnesia that has been attributed in the clinical literature to damage of the hippocampal system^1,2 has not been observed in animals with such damage. Hippocampal-system lesions in animals do markedly impair some forms of spatial memory^3,4, but the effects on other forms of memory have generally seemed minor^5,6 compared with the dramatic disorder described in man^7,8. This discrepancy between the clinical and animal literature could indicate a true evolutionary shift in the functions of the hippocampus^9,10, or, at the other extreme, it could simply reflect the use of incommensurate measures across species^11,12. (Strong support for this second interpretation has been provided by Gaffan¹³.) A third possibility, however, is that the discrepancy points to inaccurate localisation of the neuropathology in man that is responsible for the profound amnesia. Support for this last alternative comes from new evidence in monkeys indicating that a striking impairment in visual memory can be produced by the combined ablation of the hippocampal formation and the amygdaloid body, but not by ablation of either of these structures alone.