Semantic Contributions to Memory Encoding and Retrieval Across the Adult Lifespan 115 views

Healthy aging is characterized by changes to various aspects of cognition, including memory. Episodic memory – memory for when and where an event occurred – declines with age. In this dissertation, I use scalp electroencephalographic (EEG) and behavioral studies to investigate how the mechanisms underlying memory encoding and memory retrieval change over the adult lifespan. Comparisons between episodic and semantic memory – memory for general facts and concepts devoid of context – yield insights into how memory encoding and retrieval change in healthy aging. In the first chapter, I recorded EEG while young adult participants performed a delayed free recall task in which some, but not all, study words shared meaning. I find that semantic processing – attending to said shared meaning – can restore neural encoding mechanisms to ameliorate memory declines. In the second chapter, I recorded EEG while young, middle-aged and older adult participants performed a memory task in which they were explicitly directed to either encode or retrieve on a given trial. I used multivariate pattern classification analyses to measure neural engagement of memory brain states, whole-brain activity/connectivity patterns that support the encoding and retrieval of memories. I find that older adults have diminished memory state engagement relative to young and middle-aged adults, suggesting that age-related memory changes may arise from differential engagement in memory brain states. In the final chapter, I collected behavioral data in young and older adults performing a recognition memory task in which I manipulated the degree of semantic and temporal overlap between study words and included critical lures, unstudied words that semantically overlap with study words. I find that whereas young and older adults are similarly reliant on semantic relative to episodic information when they engage in false memory – remembering events differently than how they happened – the two age groups differ in their reliance on semantic relative to episodic information to support true memory. The results of the final chapter suggest that differences in the baseline orientation of attention toward the semantic or episodic dimensions of events may underlie age-related memory changes. Taken together, this dissertation provides a deeper understanding of how the mechanisms underlying memory encoding and memory retrieval change over the adult lifespan.

PHD (Doctor of Philosophy)

episodic memory; semantic memory; aging; electroencephalography

English

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2025-07-31