Mammillary Body Damage Results in Memory Impairment But Not Amnesia

Abstract

Isolated mammillary body pathology is rare, and there remains controversy as to whether such focal lesions will result in amnesia. We report two cases of lesions to the mammillary bodies arising from a suprasellar tumour. Neither case underwent radical surgical or radiotherapy treatment, which in themselves might have affected memory functioning. In both patients, extensive memory testing across a wide range of memory tasks showed relatively limited anterograde memory impairment which was mainly evident on some but not all delayed recall tasks. Neither patient showed evidence of significant retrograde amnesia. Our negative findings contrast with recent case reports, and these conflicting observations are discussed in terms of the possible role of coexistent cerebral pathology that may exacerbate the effects of mammillary body lesions to produce amnesic levels of performance. Our data point to a limited/selective role for the mammillary bodies in human memory, and raise the possibility that recovery of memory function after discrete limbic circuit lesions may only be compromised when there is more than one lesion in the Papez circuit.