Anterior Shift

Anterior shift is a phenomenon whereby peak neural activity observed during the retrieval of a visual stimulus is localized anterior to the peak activity observed during perception/encoding. In younger and older adults, we identified robust anterior shift in 4 scene- and face-selective regions of interest. Our data reveals that the anterior shift is greater in older than younger adults. Moreover, greater anterior shift within the scene-selective Parahippocampal place area was associated with worse memory for visual stimuli. This relationship was evident across both age groups. In line with work proposing a posterior (perceptual) to anterior (conceptual) gradient in the brain, these findings suggest that the anterior shift reflects a process which gradually ‘abstracts’ away the high-fidelity perceptual properties of the encoded stimulus with a shift towards relatively more gist-based mnemonic representations (with greater reliance on gist-based memories in older adults).

Age-related Neural Dedifferentiation and Cortical Reinstatement

Increasing age is associated with age-related reduction in the specificity and fidelity of neural representations at encoding and at retrieval, phenomena which are observed in the form of reduced neural differentiation at encoding (neural selectivity of category-selective cortical regions) and lower strength of cortical reinstatement at retrieval (retrieval-related reactivation of the neural activity which was initially observed at encoding). These age differences are functionally significant: neural specificity at encoding and retrieval is predictive of memory performance, and recent findings suggest that neural differentiation is sensitive to the levels of tau deposition in healthy older adults. Our recent findings demonstrate that, relative to other stimulus categories such as objects or faces, perceptual processing and subsequent retrieval of scene stimuli is associated with reduced neural selectivity. My dissertation builds on these findings and employs fMRI with simultaneous eye-tracking to examine the factors that contribute to the vulnerability of scene processing with increasing age.

Effects of Age on the Control of Recollected Content

Younger adults engage in retrieval gating, a phenomenon whereby the representations of task-irrelevant features of a mnemonic episode is attenuated during retrieval. By examining the strategic modulation of cortical reinstatement of task-relevant and task-irrelevant content in younger and older adults, we demonstrated that, unlike younger adults, older adults do not exhibit retrieval gating. These findings are compatible with other recent evidence suggesting that older adults are more likely to ‘clutter’ their memories with irrelevant information, thus potentially leading to poor memory performance.