High-resolution magnetic resonance imaging (MRI) techniques provide a unique tool for examining alterations in brain anatomy in vivo during healthy aging as well as in various age-related disease processes. In addition, such techniques make it possible to (a) relate alterations in given brain regions to the sequential development of behavioral symptoms in degenerative diseases and (b) examine the specific role of certain brain structures in human memory function because of the age or disease-re-lated occurrence of “lesions” in these structures.
The entorhinal cortex (EC) and the hippocampal formation (HF) are part of the mesial temporal lobe memory system; the EC connects the neocortex with the HF, thereby providing the latter with multimodal sensory information. Postmortem pathological studies have implicated the EC as one of the early sites of involvement in Alzheimer’s disease (AD).5,6,20,34,39 Although hippocampal atrophy has been well documented in AD and in preclinical cases using quantitative volumetric MRI techniques,8,9,11-13,22,23,26-29,36,41 such protocols have only recently been developed for the EC.21,25.
In this paper, we review work from our laboratory on alterations in entorhinal volume detected in vivo using quantitative structural MRI in various elderly cohorts, contrasting entorhinal atrophy to that seen in the HF, where appropriate. At the end of the paper, we present some preliminary data suggesting that the EC and HF play different roles in human memory function. Since the MRI techniques used in all the experiments to be described were similar, they will be detailed first.
