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sleep

7-8 hours of sleep/night is considered optimal. Most adults sleep this much. Also see sleep deprivation. Function: (benefits of sleep) 1) consolidation of recent memory, including aquisition of skills through practice [3] 2) enhances insight & creativity [3] 3) glymphatic clearance of toxic metabolites from the brain's interstitial space [5,23,29] - includes beta-amyloid* & its oligomers 4) the brain's interstitial space is increased 60% during sleep [5] 5) sleep, REM sleep [15] & slow-wave sleep [16] may diminish risk for dementia 6) longer sleep duration & better sleep efficiency in adolescents were associated with lower metabolic risk scores, including - lower abdominal adiposity - lower systolic blood pressure - serum HDL cholesterol [17] 7) healthy sleep may reduces cardiovascular risk a) adults who sleep < 6 hours/night are more likely to have subclinical noncoronary atherosclerosis [20] b) quality sleep linked to lower risk of heart failure [25] 8) U-shaped association of sleep duration with cognitive decline in older adults *> 45-50 years centered around 7 hours/night [24,28] - optimal sleep duration for adults is ~7 hours/night [35] - normal sleep duration (7-9 hr) associated with higher cognitive scores [37] - earlier sleep patterns linked to superior cognitive function [37] 9) adequate sleep may preserve cognition in preclinical & early symptomatic Alzheimer's disease [32] - adequate total sleep time preserves cognitive function - adequate time in non-REM & REM sleep preserves cognitive function - adequate slow-wave (< 1 Hz) sleep preserves cognitive function * increased risk of beta-amyloid deposition with reduced nighttime sleep occurs prior to onset of cognitive impairment or beta-amyloid deposition [31] Epidemiology: - 1/3 of US adults do not get enough sleep [9] - adults >= 65 and older years most likely to get enough sleep (74%); adults 25-44 years least likely (62%) - sufficient sleep most common among whites (67%); least common among blacks & Native Hawaiian/Pacific Islanders (54%) - people in South Dakota sleep the most, those in Hawaii sleep the least [9] Physiology: - after sleep onset, sleep usually progresses through non-REM sleep stages 1-4 within 45-60 minutes - sleep cycles oscillate with lunar phases - nights before a full moon, people go to bed later & sleep less (assessed by wrist actigraphy) - brain regions most significantly underlying the benefit of optimal sleep duration include the precentral cortex, the lateral orbitofrontal cortex & the hippocampus [35] - accurate behavioral responses to instructions to smile or frown occur in most sleep stages in healthy people & patients with narcolepsy, except in slow-wave sleep in healthy people [36] Histology: - 3 wake-promoting CNS nuclei - noradrenergic locus coeruleus - orexinergic lateral hypothalamic area - histaminergic tuberomammillary nucleus Genetics: - transcriptional repressor DEC2 regulates sleep length in mammals [30] - hDEC2-P385R that is associated with a human short sleep phenotype - 5 hours sleep may be sufficient Comparative biology: - glymphatic clearance peaks in mice when they sleep - aquaporin receptors are more highly expressed in sleep - interstitial spaces themselves expand [8] - microarousals (awakenings) at night linked to memory consolidarion in mice [34] Special laboratory: Electrophysiology: correlates of human sleep states & stages 1) awake (eyes open) a) EEG:* low amplitude, mixed (high) frequency b) electrooculogram: rapid c) electromyogram: high amplitude, variable 2) awake (eyes closed) a) EEG: low amplitude, alpha waves (8-13 Hz) dominates b) electrooculogram: absent, but slow, rolling eye movements c) electromyogram: reduced 3) Stage 1 non-REM* a) EEG: low amplitude, mixed frequency, alpha waves absent, theta activity b) electrooculogram: slow, rolling eye movements c) electromyogram: reduced 4) Stage 2 non-REM a) EEG: low amplitude, K complexes & sleep spindles b) electrooculogram: absent c) electromyogram: reduced 5) Stage 3 non-REM a) EEG: increased amplitude, decreased frequency in 20-50% of record, dominated by delta waves (0.5-2.0 Hz) b) electrooculogram: absent c) electromyogram: reduced 6) Stage 4 non-REM (slow wave sleep) a) EEG: > 50% dominated by delta waves b) electrooculogram: absent c) electromyogram: reduced 7) REM a) EEG: low amplitude, mixed frequency, theta & beta waves b) electrooculogram: rapid, conjugate c) electromyogram: absent * REM: rapid eye movement sleep EEG: electroencephalogram Management: - optimal sleep duration (National Sleep Foundation) [7] - newborns (0-3 months of age): 14-17 hours/day [22] - infants (4-12 months): 12-16 hours/day [10,22] - toddlers (1-2 years): 11-14 hours/day [22] - preschool children (3-5 years): 10-13 hours/day [22] - school-age children (6-12 years): 9-12 hours/day [10] - teenagers: 8-10 hours/day [10] (8.5-9.5 hours [6]) - adults <= 25 years of age: 7-9 hours/day - adults 26-64 years of age: 7-9 hours//day - older adults >= 65 years of age: 7-8 hours/day - adults 38-73 years: ~7 hours/night [35] - naps, extending sleep on weekends, & caffeine do not restore optimal daytime alertness - middle school & high school should be started no earlier than 8:30 AM [6,12] - eighth graders starting school before 8 AM have decreased sleep duration, lower grades, & lower rates of homework completion [14] - delay of school start time of secondary schools from 7:50 to 8:45 a.m. results in longer sleep duration (6 hr 50 min to 7 hr 24 min) associated with less sleepiness & improved grades in high-school students - exercise & Tai chi may improve quality of sleep [27] Notes: Other sleep factors: - sleeping in prone position lowers systolic blood pressure in men as much as 15 mm Hg [4] - uninterrupted sleep at 6 & 12 months of age is not associated with later development [18]

Related

age-associated changes in sleep glymphatic clearance; glymphatic flow (glymphatic system) sleep & blood pressure sleep deprivation; insufficient sleep syndrome sleep disorder

Specific

non-REM sleep rapid eye movement (REM) sleep siesta (daytime nap, catnap)

General

physiologic process

References

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