Age-Related Differences in Mnemonic Neural Representations: Perceptual and Semantic Contributions
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Preliminary evidence demonstrates that age-related differences in episodic memory performance become greater in tasks that have greater perceptual demands (e.g., task stimuli are visually degraded), but are attenuated in tasks that have greater semantic demands (e.g., task requires utilizing previous knowledge). This work suggests that age-related differences in how perceptual and semantic information are represented in the brain have an impact on episodic memory. Broadly, the goal of this thesis was to investigate this idea. To investigate this goal, while undergoing functional magnetic resonance imaging scanning, samples of younger and older adults studied and later retrieved their memories of pictures of either scenes (Study 1 and 2) or objects (Study 3). The first two studies found that, compared to younger adults, in older adults, (1) in occipitotemporal cortex, the quality of perceptual-related representations was attenuated, but, intriguingly, (2) in anterior temporal lobes and prefrontal cortex, the quality of semantic-related representations was similar and even enhanced; these effects were found to be related to episodic memory. Study 1 demonstrated this pattern in individual brain regions and Study 2 demonstrated that this pattern was also present in how information was distributed across the whole-brain network. In Study 3 it was found that these age-related differences in functional neural representations are the result of age-related visual signal loss and compensatory semantic-enhancing mechanisms. Taken together, the three studies highlight that age-related differences in neural representations have an impact on cognition and especially episodic memory.
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