Relational memory and the hippocampus: Representations and methods

Alex Konkel

doi:10.3389/neuro.01.023.2009

Abstract

Since the discovery of the importance of the hippocampus for normal memory, considerable research has endeavored to characterize the precise role played by the hippocampus. Previously we have offered the relational memory theory, which posits that the hippocampus forms representations of arbitrary or accidentally occurring relations among the constituent elements of experience. In a recent report we emphasized the role of the hippocampus in all manner of relations, supporting this claim with the finding that amnesic patients with hippocampal damage were similarly impaired on probes of memory for spatial, sequential, and associative relations. In this review we place these results in the context of the broader literature, including how different kinds of relational or source information are tested, and consider the importance of specifying hippocampal function in terms of the representations it supports.

Highlights

Since the discovery of the importance of the hippocampus for normal memory, considerable research has endeavored to characterize the precise role played by the hippocampus
CHARACTERIZING THE FUNCTIONAL ROLE OF THE HIPPOCAMPUS That the hippocampus plays a critical role in memory has been clear since the documenting of severe amnesia following temporal lobe resection in patient H.M. (Scoville and Milner, 1957)
An extraordinary amount of research has been directed at characterizing the functional role the hippocampus plays in memory, leading various authors to emphasize, among other things, spatial memory or cognitive mapping (O’Keefe and Nadel, 1978), declarative memory (Cohen, 1984; Cohen and Eichenbaum, 1993; Squire et al, 2004), explicit memory (Graf and Schacter, 1985), recollection (Aggleton and Brown, 2006; Ranganath et al, 2004), and relational memory (Cohen and Eichenbaum, 1993; Eichenbaum and Cohen, 2001)

Summary

Relational memory and the hippocampus

Declarative memory Memory for facts and events, to be contrasted with procedural memory, which supports the ability to acquire and express skills (or the difference between “knowing that” and “knowing how”). Many studies have gone on to report spatial correlates of hippocampal activity or hippocampal dependence of spatial memory performance, based on allocentric spatial relations, in animals and in humans (see Bird and Burgess, 2008; Table 1) Both the animal and human literatures are filled with numerous findings from other studies documenting hippocampal involvement in relational tasks with no critical spatial component (see Cohen et al, 1999; Eichenbaum and Cohen, 2001; Table 1), making it difficult to reconcile a solely spatial account of hippocampal function. Using a subsequent memory analysis with yes/no item recognition and forced-choice source judgments, Uncapher et al (2006) had participants make a living/non-living judgment on words in one of four colors located in one of four quadrants on the screen They found that the hippocampus was more active when both sources were later remembered than if only one were remembered, whereas the perirhinal cortex was

Result

Trials to criterion

Patients impaired

Patients impaired at detecting shifts

Triplets of computergenerated patterns

Patients were impaired at the conjunction