Working Memory for Complex Scenes: Age Differences in Frontal and Hippocampal Activations

Park, Denise C.; Welsh, Robert C.; Marshuetz, Christy; Gutchess, Angela; Mikels, Joseph A.; Polk, Thad A.; Noll, Douglas C.; Taylor, Stephan F. · 2003 · OpenAlex-citations

DOI: 10.1162/089892903322598094

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Summary

This study investigates age-related differences in neural activation within the frontal and hippocampal regions during working memory tasks involving complex, meaningful scenes. While behavioral performance on working memory tasks typically declines with age, the underlying neural mechanisms remain complex, with prior research suggesting both compensatory and dysfunctional patterns of frontal recruitment. The authors specifically address the under-explored role of the hippocampus in working memory for older adults, hypothesizing that younger adults would exhibit greater hippocampal activation during maintenance, while older adults might show increased frontal activation at retrieval, potentially as a compensatory response to reduced hippocampal efficiency. The researchers employed an event-related functional magnetic resonance imaging (fMRI) design with 11 younger and 10 older adults. Participants performed two conditions: an "extended visual" condition involving passive viewing of a scene for six seconds, and a "maintenance" condition requiring active mental rehearsal of a scene for four seconds after a two-second presentation. Both conditions were followed by a probe fragment requiring a recognition judgment. This design allowed the separation of neural activations into encoding, maintenance, and retrieval phases. Behavioral data indicated that accuracy on the probe task was largely equivalent across age groups and conditions, providing a controlled basis for interpreting neural differences. However, older adults exhibited slower reaction times, particularly on hit trials. Neuroimaging results revealed distinct age-related patterns in hippocampal and frontal activations. During the maintenance interval, younger adults showed significantly increased left anterior hippocampal activation in the extended visual condition compared to maintenance, a differentiation not observed in older adults. Although older adults did not show sustained hippocampal activation above baseline during the entire maintenance period, they did exhibit significant activation at the onset of the maintenance phase, suggesting automatic relational processing remains intact. Crucially, during the probe interval, older adults demonstrated significantly greater bilateral inferior frontal cortex activation than younger adults. This increased frontal recruitment occurred despite equivalent behavioral accuracy and could not be fully explained by longer reaction times. The findings demonstrate that older adults engage frontal and hippocampal structures qualitatively differently than younger adults during working memory tasks, even when behavioral performance is equivalent. The reduced hippocampal differentiation in older adults suggests a decline in hippocampal function associated with relational processing, consistent with evidence of age-related hippocampal volume loss. The increased frontal activation in older adults at retrieval may represent a compensatory mechanism to offset decreased hippocampal efficiency, or it may reflect increased task difficulty. These results highlight that age-related changes in working memory involve not just quantitative declines in performance, but fundamental shifts in the neural networks recruited to maintain and retrieve complex visual information.

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• working memory