Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

https://www.zora.uzh.ch/id/eprint/77770/1/physiol_rev_93.pdf

About sleep's role in memory

In previous analyses of the occurrence of central (CSA) and obstructive sleep apnea (OSA) in patients with congestive heart failure (CHF), only men were studied and risk factors for these disorders were not well characterized. We therefore analyzed risk factors for CSA and OSA in 450 consecutive patients with CHF (382 male, 68 female) referred to our sleep laboratory. Risk factors for CSA were male gender (odds ratio [OR] 3.50; 95% confidence interval [CI], 1.39 to 8.84), atrial fibrillation (OR 4.13; 95% CI 1.53 to 11. 14), age > 60 yr (OR 2.37; 95% CI 1.35 to 4.15), and hypocapnia (PCO(2 ) 35 kg/m(2), 6.10; 95% CI 2.86 to 13.00); whereas, in women, age was the only important risk factor (OR for age > 60 yr, 6.04; 95% CI 1.75 to 20.0). We conclude that historical information, supplemented by a few simple laboratory tests may enable physicians to risk stratify CHF patients for the presence of CSA or OSA, and the need for diagnostic polysomnography for such patients. Sin DD, Fitzgerald F, Parker JD, Newton G, Floras JS, Bradley TD. Risk factors for central and obstructive sleep apnea in 450 men and women with congestive heart failure.

https://www.atsjournals.org/doi/pdf/10.1164/ajrccm.160.4.9903020?firstindex=0&fulltext=sleep+apnea+congestive+heart

Risk Factors for Central and Obstructive Sleep Apnea in 450 Men And Women with Congestive Heart Failure

Total sleep restriction in humans is associated with increased daytime sleepiness, decreased performance, and hormonal/metabolic disturbances. The effects of mild chronic sleep restriction that mimic real life are not known. To assess the effects of modest sleep restriction from 8 to 6 h/night for 1 wk, 25 young, healthy, normal sleepers (12 men and 13 women) were studied for 12 consecutive nights in the sleep laboratory. After 1 wk of sleep restriction, although subjects’ nighttime sleep was deeper, subjects were significantly sleepier (multiple sleep latency test) and performed worse in four primary variables of psychomotor vigilance test (both P < 0.01). Furthermore, 24-h secretion of IL-6 was increased by 0.8 ± 0.3 pg/ml (P < 0.05) in both sexes, whereas TNFα was increased only in men. Also, the peak cortisol secretion was lower after sleep restriction than at baseline, and this difference was stronger in men (55.18 ± 24.83 nmol/liter; P < 0.05) than in women (35.87 ± 24.83 nmol/liter; P < 0.16). We c...

Adverse Effects of Modest Sleep Restriction on Sleepiness, Performance, and Inflammatory Cytokines

Study objective Most but not all epidemiologic evidence suggests a female predisposition of insomnia. We applied meta-analytic methods to investigate sex differences in the risk of insomnia among the published epidemiologic studies. Design Meta-analysis with Comprehensive Meta-Analysis (Englewood, NJ); 9 different analyses were performed to investigate the sex difference of insomnia among different conditions. Setting A comprehensive search of the medical literature databases was performed to identify epidemiologic studies of insomnia. A rolling snowball method was also used. Participants General population. Interventions N/A. Result Thirty-one related papers were found, but 2 studies only reported the subtype prevalence of insomnia. All other studies (1,265,015 participants, female/male: 718,828/546,187) were included in the overall analysis of insomnia. A risk ratio of 1.41 [95% confidence interval: 1.28-1.55] for female versus male was found. The female excess in the risk of insomnia in large and quality studies was much higher than that of small and nonquality studies. The trend of female predisposition was consistent and progressive across age, with more significance in the elderly. The use of various criteria and frequency and duration of insomnia did not influence the predisposition of female in the risk of developing insomnia. Although obvious female excess in the risk of insomnia exists among different regions, there was a relatively lower female excess in East Asia. Conclusion This meta-analysis confirmed a female predisposition of insomnia. Further studies will be needed to examine the roles of different factors in leading to the sex difference of insomnia.

/pdf/sex-differences-in-insomnia-a-meta-analysis-1hztp2jllg.pdf

Sex differences in insomnia: a meta-analysis.

Background Polysomnography is used to assess sleep quality and to gauge the functional effect of sleep disorders. Few population-based data are available to estimate the variation in sleep architecture across the population and the extent to which sleep-disordered breathing (SDB), a common health condition, contributes to poor sleep independent of other factors. The objective of this study was to describe the population variability in sleep quality and to quantify the independent associations with SDB. Methods Cross-sectional analyses were performed on data from 2685 participants, aged 37 to 92 years, in a community-based multicenter cohort study. Dependent measures included the percentage time in each sleep stage, the arousal index, and sleep efficiency. Independent measures were age, sex, ethnicity, comorbidity status, and the respiratory disturbance index. Results Lighter sleep was found in men relative to women and in American Indians and blacks relative to other ethnic groups. Increasing age was associated with impaired sleep in men, with less consistent associations in women. Notably, women had, on average, 106% more slow wave sleep. Sleep-disordered breathing was associated with poorer sleep; however, these associations were generally smaller than associations with sex, ethnicity, and age. Current smokers had lighter sleep than ex-smokers or never smokers. Obesity had little effect on sleep. Conclusions Sleep architecture varies with sex, age, ethnicity, and SDB. Individual assessment of the effect of SDB on sleep quality needs to account for other host characteristics. Men, but not women, show evidence of poorer sleep with aging, suggesting important sex differences in sleep physiology.

https://jamanetwork.com/journals/jamainternalmedicine/articlepdf/216692/ioi20991.pdf

The Effects of Age, Sex, Ethnicity, and Sleep-Disordered Breathing on Sleep Architecture

The sleep of 52 healthy paid subjects (23 male) divided into three age-bands (20–34, 35–49 and 50–70 y) were recorded at night in their homes for a total of 190 subject-nights while following their normal daily activities and habitual sleep-wake schedule. There was a shortening in both nocturnal total sleep period and total sleep time (TST) with age, the oldest group sleeping 46 min less than the youngest. Also, the mid-point of sleep occurred 32 min earlier in the oldest group compared with the youngest group. The reduction in TST with age was due, in part, to increased wake periods within sleep. The youngest subjects showed more Movement Time which progressively decreased with age while the amount of stage 1 increased with age. The amount of slow-wave sleep (SWS, stages 3+4) was reduced, stage 4 was more than halved, while REM was slightly reduced with age. There were far fewer significant gender differences in the sleep variables: males, particularly in the middle and oldest age bands, had more stage 1 than females, while females had more SWS, particularly stage 3, than males. In general, despite relatively limited subject selection criteria, there was good agreement with previous laboratory-based normative sleep values for the effect of age and gender.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2869.1998.00103.x

Alison Watson

Papers

A field study of age and gender differences in habitual adult sleep