The Role of the Human Entorhinal Cortex in a Representational Account of Memory.

Heidrun Schultz,Tobias Sommer,Jan Peters

doi:10.3389/fnhum.2015.00628

Abstract

Connectivity studies in animals form the basis for a representational view of medial temporal lobe (MTL) subregions. In this view, distinct subfields of the entorhinal cortex (EC) relay object-related and spatial information from the perirhinal and parahippocampal cortices (PRC, PHC) to the hippocampus (HC). Relatively recent advances in functional magnetic resonance imaging (fMRI) methodology allow examining properties of human EC subregions directly. Antero-lateral and posterior-medial EC subfields show remarkable consistency to their putative rodent and nonhuman primate homologs with regard to intra- and extra-MTL functional connectivity. Accordingly, there is now evidence for a dissociation of object-related vs. spatial processing in human EC subfields. Here, variance in localization may be integrated in the antero-lateral vs. posterior-medial distinction, but may additionally reflect process differences. Functional results in rodents further suggest material-specific representations may be more integrated in EC compared to PRC/PHC. In humans, however, evidence for such a dissociation between EC and PRC/PHC is lacking. Future research may elucidate on the unique contributions of human EC to memory, especially in light of its high degree of intrinsic and extrinsic connectivity. A thorough characterization of EC subfield function may not only advance our understanding of human memory, but also have important clinical implications.

Highlights

A small structure embedded in the anterior temporal lobe (Pruessner et al, 2002), the entorhinal cortex (EC) has garnered attention beyond the neuroscientific community through the 2014 Nobel Prize in Physiology or Medicine to John O’Keefe, May-Britt Moser and Edvard I
Studies in humans underline its importance for memory: EC may be affected early in Alzheimer’s disease (AD) and mild cognitive impairment (MCI; deToledo-Morrell et al, 2004; Pihlajamäki et al, 2009; Markesbery, 2010; Khan et al, 2014)
Anatomical connectivity studies in rodents and nonhuman primates have informed functional accounts of medial temporal lobe (MTL) information processing, with respect to memory (Davachi, 2006; Eichenbaum et al, 2007) and, more controversially, perception (Graham et al, 2010) (Note that we focus on visual connections, all sensory modalities project to the MTL; Burwell, 2000)

Summary

INTRODUCTION

A small structure embedded in the anterior temporal lobe (Pruessner et al, 2002), the entorhinal cortex (EC) has garnered attention beyond the neuroscientific community through the 2014 Nobel Prize in Physiology or Medicine to John O’Keefe, May-Britt Moser and Edvard I. EC, together with the adjacent perirhinal cortex (PRC), parahippocampal cortex (PHC) and HC, forms the medial temporal lobe (MTL) system, considered pivotal to memory (Squire and Zola-Morgan, 1991; Eichenbaum et al, 2007). A thorough body of connectivity studies in animals has identified EC as a relay station within MTL, passing information between HC and neocortex (Lavenex and Amaral, 2000; van Strien et al, 2009). Closely tied to its role in navigation (Buzsáki and Moser, 2013; Moser et al, 2015), EC’s role in memory has often been investigated in a separate line of research

Human Entorhinal Cortex and Memory

CONNECTIVITY AND FUNCTIONAL IMPLICATIONS

CONCLUSION