Memory, Relational Representations, and the Long Reach of the Hippocampus

Abstract

What is memory and what is it for? How does the brain represent our experiences and use stored information to guide future behavior? In this chapter, we explore the contributions of the hippocampus to memory and to the many aspects of behavior it supports. We start with discussion of the view that hippocampal-dependent memory is a fundamentally relational and compositional representation system, supporting the binding of even arbitrary or accidental relations among constituent elements of experience into memory, representing experience via links that maintain the separate representational integrity of those elements rather than fusing them into wholistic or unitized memories, and supporting the subsequent reactivation of these relational representations. The major portion of the chapter discusses the surprisingly long reach of hippocampal influence, due to the relational and flexible nature of its representations. Hippocampal influence extends both across all manner of relations, including spatial, temporal, and associative relations, and across timescales, including not only the classically described role in long-term memory, but also on the timescale of short-term or working memory and even in moment-to-moment processing. Furthermore, the long reach of hippocampal influence is seen in the flexible use of relational representations in service of a rich variety of behavioral repertoires, helping critically in guiding flexible and adaptive choices—uses of hippocampal representations that clearly stretch the classical definition of memory. Finally, we consider the debt owed to clinical studies in providing insights about the nature of relational representations and about the extent of hippocampal influence.