Sleep is known to dramatically enhance memory for recently learned information in healthy young adults. This general finding extends across all major memory domains, and has been observed following a full night of sleep and even following brief daytime naps. Unfortunately, almost nothing is known about whether this mnemonic benefit of sleep extends into the later years of life. The three studies proposed in this application will closely examine sleep-dependent memory processing across the adult lifespan, in healthy young and elderly subjects, and in patients with mild Alzheimer's disease (AD). Motor skill and declarative memory performance will be assessed in each of these studies. In addition to the assessment of memory performance, these studies will shed light on the neural correlates of sleep-dependent memory processing in each of these three groups using high-density EEG recordings. The studies will be conducted at the Center for Sleep and Cognition (CSC) in Boston, MA, and clinical training in AD will take place at the VA Boston Health Care System in Jamaica Plain, MA. All studies will employ a cross-over design to increase statistical power, and all subjects will undergo high-density EEG recordings during sleep. In the first study, healthy young and elderly subjects will make two visits to the CSC. In the Wake-first condition, subjects will come to the lab at 9am for task training. They will return to the lab at 9pm for retesting, and again at 9am the following morning for a second retest after a night of EEG recorded sleep. In the Sleep-first group subjects will train in the evening, with retest sessions at 9am and 9pm the following day. This design will allow for a comprehensive look at the trajectory of memory over time, the effect of sleep and wake on memory processing, and the sleep-related neural correlates of this memory processing, in both young and elderly individuals. The second study will examine the effects of a daytime nap on memory in healthy young and elderly subjects. Memory retention in this study will be assessed shortly after the nap, and 48hrs later to assess the sustained effects of a daytime nap on memory. To begin our investigation of sleep and memory in normal and pathological aging, the third study, also a nap study, will examine whether a daytime nap confers similar memory benefits in healthy elderly subjects and mild AD patients. Each of these studies will substantially advance our understanding of the nature of sleep-dependent memory processing, and the effect of sleep on memory over the adult life span. The results of these studies will help to reshape our thinking about the value of sleep as a therapeutic tool to ameliorate age-related memory decline.
Sleep facilitates the processing of motor and declarative memories in healthy young adults. However, it remains unknown whether this robust sleep-dependent memory enhancement extends to healthy and impaired elderly populations. The proposed studies will closely examine and compare the effects of sleep on memory processing in healthy young and elderly individuals, as well as in patients with mild Alzheimer's disease (AD), and will identify the neurophysiological correlates of these effects in each population. It is our belief that these findings will provide evidence that the memory deficits observed in healthy elderly and mild AD individuals can be ameliorated through the manipulation of the patterns and physiological properties of their sleep.
