Age-related changes in the cognitive function of sleep.

Healthy aging is characterized by a diminished quality of sleep with decreased sleep duration and increased time awake after sleep onset. Older adults awaken more frequently and tend to awaken less from rapid eye movement (REM) sleep and more from non-REM (nREM) sleep than young adults. Sleep architecture also begins changing in middle age leading to a dramatic decrease in the deepest stage of nREM-slow wave sleep (SWS)-as aging progresses. Other less marked nREM changes include reduced numbers of sleep spindles and K-complexes. In contrast, the amount of REM diminishes only slightly. Both circadian and homeostatic sleep-regulatory processes are affected by aging. Circadian rhythms of temperature, melatonin, and cortisol are phase advanced and their amplitude diminished. An increased number of nocturnal awakenings and diminished daytime sleepiness suggest diminished homeostatic sleep pressure. A variety of endocrine and neuromodulatory changes (e.g., reduced growth hormone and dopamine levels) also accompany healthy aging. Healthy aging is characterized by declines in working memory and new episodic memory performance with relative sparing of semantic memory, recognition memory, and priming. Memory systems impacted by aging are associated with volumetric and functional changes in fronto-striatal circuits along with more limited changes in medial temporal structures (in which larger aging-related changes suggest neuropathology). Cross-sectional studies generally associate poorer sleep quality with poorer neuropsychological functioning. However, paradoxically, older adults appear to be more resistant to the cognitive effects of sleep deprivation, restriction, and fragmentation than younger adults. A new and expanding field examines the interaction between aging and sleep-dependent memory consolidation. Among forms of learning displaying prominent sleep-dependent consolidation in young adults, motor-sequence learning displays loss of sleep-dependent consolidation with aging whereas sleep-dependent consolidation of verbal declarative memory appears spared. Findings suggest that improving sleep through behavioral or pharmacological treatments may enhance cognition and performance in older adults.