Abstract
Aging is associated with a decline in episodic memory function. This is accompanied by degradation of and functional changes in the medial temporal lobe (MTL) which subserves mnemonic processing. To date no study has investigated age-related functional change in MTL substructures during specific episodic memory processes such as intra-item associative memory. The aim of this study was to characterize age-related change in the neural correlates of intra-item associative memory processing. Sixteen young and 10 older subjects participated in a compound word intra-item associative memory task comprising a measure of associative recognition memory and a measure of recognition memory. There was no difference in performance between groups on the associative memory measure but each group recruited different MTL regions while performing the task. The young group recruited the left anterior hippocampus and posterior parahippocampal gyrus whereas the older participants recruited the hippocampus bilaterally. In contrast, recognition memory was significantly worse in the older subjects. The left anterior hippocampus was recruited in the young group during successful recognition memory whereas the older group recruited a more posterior region of the left hippocampus and showed a more bilateral activation of frontal brain regions than was observed in the young group. Our results suggest a reorganization of the neural correlates of intra-item associative memory in the aging brain.
Highlights
The medial temporal lobes (MTL) contain structures that are crucial for memory processing, such as the hippocampus, perirhinal cortex, and the parahippocampal gyrus
Investigating within group performance, we found significant differences in accuracy between identical and recombined items [85 vs. 57%, t (30) = 4.951, p = < 0.001], between recombined and novel items [57 vs. 95%, t (30) = −7.535, p = < 0.001], and between identical and novel items [85 and 95%, t (30) = −3.162, p = 0.004] in the young group
No significant difference was found in response latency between identical and novel items
Summary
The medial temporal lobes (MTL) contain structures that are crucial for memory processing, such as the hippocampus, perirhinal cortex, and the parahippocampal gyrus. Damage to these structures invariably results in episodic memory impairment (Scoville and Milner, 1957). The hippocampus is implicated in betweendomain associative memory (Mayes et al, 2004; Konkel et al, 2008), that is the high level integration and “binding” of perceptual and conceptual information which are processed and stored in distal brain regions with weak or no direct connectivity with each other. Existing evidence shows that memory processing of verbal information or information with a semantic content is lateralized to the anterior regions of the left MTL (Parsons et al, 2006; Ford et al, 2010)
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