Sleep and circadian effects on memory in healthy young and older adults

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Project Summary/Abstract Sleep is widely believed to play a critical role in memory consolidation, but the exact nature of this role remains controversial. Sleep disturbances are commonly reported in patients with neurologic and psychiatric disorders such as Alzheimer’s disease[1, 2] or schizophrenia [3] as well as in normal healthy aging [4], raising the possibility that alterations in sleep may underlie some of the cognitive impairments reported in these populations. Moreover, recent CDC data estimates that over a third of U.S. adults experience chronic insufficient sleep [5], which may have immediate and long-term consequences on cognition. While there is abundant evidence that sleep is important for learning [6], other factors such as circadian timing, age, and individual differences may also have an effect on learning, both directly and indirectly via their effects on sleep. These areas must be addressed in order to further develop our understanding of the complex relationship between sleep and memory. We have previously found circadian- and wake-dependent influences on performance in healthy young and older adults, using several different neurobehavioral tests [7, 8]. However, it is unclear whether the duration of wakefulness and biological timing impact memory tasks in a similar way, particularly among older adults. Additionally, we have previously demonstrated that performance on a face-name association memory task was enhanced in young adults when an overnight sleep opportunity was included in the retention interval [9], but were unable to identify an association between performance on this task and sleep duration or any sleep stage. Here, we propose to investigate whether circadian timing or duration of time awake affects short-term word-pair or face-name memory and whether this differs between young and older adults, using existing data collected from two different memory tasks administered over the course of a highly controlled inpatient sleep and circadian rhythm study. In addition, we propose to follow up on our previous study by collecting new data to investigate whether sleep duration or structure enhance performance on a face-name memory task, using repeated testing across multiple nights in the same individuals. Understanding how sleep, duration of waking, and biological timing impact memory and how those impacts may differ with healthy aging is critical to understanding cognitive deficits in populations with disrupted sleep.