Studies on H.M. generated five main findings: that memory is a distinct psychological function, that amnesia spares short-term and working memory, that amnesia is an impairment of declarative and episodic memory, that the hippocampus is a core brain structure supporting memory, and that the hippocampus supports the permanent consolidation of memories. Each of these basic findings has recently been challenged, but a consideration of these studies suggests the new observations serve to support the original findings on H.M. and improve our understanding of the memory functions of the hippocampal system.

Theoretical arguments and empirical data are presented in favor of the hypothesis that the hippocampal system supports a declarative memory capacity in animals as well as humans. This view is advanced by identifying two prominent characteristics of human declarative memory and by operationalizing and evaluating them using both experimental lesion and single unit recording studies on animals. First, hippocampal processing is not selective to any particular category of learning materials; instead, it supports comparisons among all kinds of information in memory, resulting in a representation of critical relations between items. Conversely, individual representations are supported outside the hippocampal system. Second, hippocampal-dependent, relational memory representations involve a flexible organization that permits inferences from memory in novel situations. Conversely, hippocampal-independent individual representations can support only repetition of procedures acquired during original learning. Correspondences between the neuropsychological and neurophysiological findings presented serve to indicate how these properties of hippocampal representation support declarative memory across behavioral paradigms and across species.