Making and Retaining New Memories: The Role of the Hippocampus in Associative Learning and Memory

Abstract

The groundbreaking description of the amnesic patient H.M. in the 1950s (Scoville and Milner 1957) demonstrated for the first time that the structures of the medial temporal lobe are critical for our ability to learn and retain new long-term memories for facts and events. This critical form of memory is referred to as declarative memory in humans (Squire et al. 2004) and relational memory in animals (Eichenbaum et al. 1999). The development of powerful animal models of human amnesia in monkeys (Zola-Morgan and Squire 1990; Mishkin 1978; Zola and Squire 2000; Suzuki et al. 1993) and in rodents (Bunsey and Eichenbaum 1993,1995, 1996; Fortin et al. 2002), together with detailed neuroanatomical studies (Suzuki and Amaral 1994a,b; Burwell and Amaral 1998a,b), demonstrated definitively that the key medial temporal lobe structures important for declarative/relational memory include the hippocampus together with the surrounding entorhinal, perirhinal and parahippocampal cortices. While this convergence of studies in humans and animals has provided detailed information about the pattern of memory impairment following a wide range of lesions to the medial temporal lobe, less information is known about how individual cells in the intact medial temporal lobe participate in the acquisition, consolidation or retrieval of various forms of declarative/relational memory.