Associations between sleep and memory in aging
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The goal of this dissertation was to understand how changes in sleep influence memory performance in healthy older adults. Previous research suggests that older individuals experience parallel declines in sleep and episodic memory. These age-related changes appear to be linked such that sleep disruptions contribute to deficits in memory performance. We examined the components of episodic memory that changed following sleep loss and correlated with aspects of sleep physiology. Healthy older adults completed two overnight sessions: an in-lab sleep recording session and a 24-hour sleep deprivation session. The morning after each sleep manipulation, participants completed both episodic memory and sustained attention tasks. We applied computational models, specifically drift-diffusion models, to the episodic memory tasks to examine whether sleep loss affected memory indirectly through lapses in sustained attention (vigilance hypothesis) or specifically through declines in the strategic processes associated with memory (neuropsychological hypothesis). Our results showed that memory functions that depend on processes associated with the prefrontal cortex were impaired following sleep deprivation. In addition, sleep loss caused a small but robust impairment in sustained attention. Since multiple cognitive processes were impaired by sleep loss in older adults, these findings do not provide unequivocal support for either the neuropsychological hypothesis or the vigilance hypothesis. In addition, we explored which aspects of sleep physiology (recorded during the sleep session) optimized components of memory performance. Our results illustrated that more slow wave power during sleep was correlated with higher next-day source memory strength. Additionally, individuals who spent more time in slow wave sleep had better memory retention. These results support further efforts to investigate sleep as a general indicator of cognitive function across the lifespan and highlight the importance of reinforcing healthy sleep behaviors as a method to preserve cognitive functioning in older adults.