Cannon, Barbara, and Jan Nedergaard. Brown Adipose Tissue: Function and Physiological Significance. Physiol Rev 84: 277–359, 2004; 10.1152/physrev.00015.2003.—The function of brown adipose tissue i...

Brown Adipose Tissue: Function and Physiological Significance

Most current models in health psychology assume that stress adversely affects physical health. We re-examined this assumption by reviewing extensive data from the literature and from six samples of our own, in which we collected measures of personality, health and fitness, stress, and current emotional functioning. Results indicate that self-report health measures reflect a pervasive mood disposition of negative affectivity (NA); self-report stress scales also contain a substantial NA component. However, although NA is correlated with health compliant scales, it is not strongly or consistently related to actual, long-term health status, and thus will act as a general nuisance factor in health research. Because self-report measures of stress and health both contain a significant NA component, correlations between such measures likely overestimate the true association between stress and health. Results demonstrate the importance of including different types of health measures in health psychology research.

Health complaints, stress, and distress: exploring the central role of negative affectivity.

Background Sleep duration may be an important regulator of body weight and metabolism. An association between short habitual sleep time and increased body mass index (BMI) has been reported in large population samples. The potential role of metabolic hormones in this association is unknown. Methods and Findings Study participants were 1,024 volunteers from the Wisconsin Sleep Cohort Study, a population-based longitudinal study of sleep disorders. Participants underwent nocturnal polysomnography and reported on their sleep habits through questionnaires and sleep diaries. Following polysomnography, morning, fasted blood samples were evaluated for serum leptin and ghrelin (two key opposing hormones in appetite regulation), adiponectin, insulin, glucose, and lipid profile. Relationships among these measures, BMI, and sleep duration (habitual and immediately prior to blood sampling) were examined using multiple variable regressions with control for confounding factors. A U-shaped curvilinear association between sleep duration and BMI was observed. In persons sleeping less than 8 h (74.4% of the sample), increased BMI was proportional to decreased sleep. Short sleep was associated with low leptin (p for slope = 0.01), with a predicted 15.5% lower leptin for habitual sleep of 5 h versus 8 h, and high ghrelin (p for slope = 0.008), with a predicted 14.9% higher ghrelin for nocturnal (polysomnographic) sleep of 5 h versus 8 h, independent of BMI.

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Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index

To determine whether a cumulative sleep debt (in a range commonly experienced) would result in cumulative changes in measures of waking neurobehavioral alertness, 16 healthy young adults had their sleep restricted 33% below habitual sleep duration, to an average 4.98 hours per night [standard deviation (SD) = 0.57] for seven consecutive nights. Subjects slept in the laboratory, and sleep and waking were monitored by staff and actigraphy. Three times each day (1000, 1600, and 2200 hours) subjects were assessed for subjective sleepiness (SSS) and mood (POMS) and were evaluated on a brief performance battery that included psychomotor vigilance (PVT), probed memory (PRM), and serial-addition testing, Once each day they completed a series of visual analog scales (VAS) and reported sleepiness and somatic and cognitive/emotional problems. Sleep restriction resulted in statistically robust cumulative effects on waking functions. SSS ratings, subscale scores for fatigue, confusion, tension, and total mood disturbance from the POMS and VAS ratings of mental exhaustion and stress were evaluated across days of restricted sleep (p = 0.009 to p = 0.0001). PVT performance parameters, including the frequency and duration of lapses, were also significantly increased by restriction (p = 0.018 to p = 0.0001). Significant time-of-day effects were evident in SSS and PVT data, but time-of-day did not interact with the effects of sleep restriction across days. The temporal profiles of cumulative changes in neurobehavioral measures of alertness as a function of sleep restriction were generally consistent. Subjective changes tended to precede performance changes by 1 day, but overall changes in both classes of measure were greatest during the first 2 days (P1, P2) and last 2 days (P6, P7) of sleep restriction. Data from subsets of subjects also showed: 1) that significant decreases in the MSLT occurred during sleep restriction, 2) that the elevated sleepiness and performance deficits continued beyond day 7 of restriction, and 3) that recovery from these deficits appeared to require two full nights of sleep. The cumulative increase in performance lapses across days of sleep restriction correlated closely with MSLT results (r = -0.95) from an earlier comparable experiment by Carskadon and Dement (1). These findings suggest that cumulative nocturnal sleep debt had a dynamic and escalating analog in cumulative daytime sleepiness and that asymptotic or steady-state sleepiness was not achieved in response to sleep restriction.

/pdf/cumulative-sleepiness-mood-disturbance-and-psychomotor-3dmt6gtthk.pdf

Cumulative sleepiness, mood disturbance, and psychomotor vigilance performance decrements during a week of sleep restricted to 4-5 hours per night

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

Energy conservation and sleep

The relative effects of extended sleep, sleep deprivation, and shifts of accustomed sleep time on subsequent performance and mood were studied. Ten regular 2400–0800 sleepers worked on E-paced addition and vigilance tasks, and completed an adjective check list to rate their mood following 2100-0800 extended, 2100-0500 advanced-shift, 2400-0800 habitual, 0300-0800 deprivation, and 0300-1100 delayed-shift conditions of sleep. Accuracy and speed of response on the vigilance task were significantly poorer, and negative affect was significantly greater after the conditions of shifted sleep and altered sleep duration than after the habitual sleep condition. Changes in the mood and performance measures were unrelated to prior sleep length or any specific alterations in the electrophysiological patterns of sleep.

Performance and mood following variations in the length and timing of sleep.

Publisher Summary A vast amount of research on sleep has been generated during the past two decades and much has been learned about its phenomenology and underlying physiological and biochemical mechanisms. Yet the biological function of sleep remains enigmatic. A recent approach that might shed light on this question is to study sleep in relationship to behaviorally similar states—states whose biological function is obvious. Hibernation and shallow torpor are two such states. Although the mechanism underlying hibernation and torpor are not completely understood, there can be little doubt that their biological function is that of energy conservation. We propose that sleep constitutes another, albeit less well recognized, variation on the theme of mammalian dormancy—that is functionally related to hibernation and torpor. This chapter reviews the behavioral and physiological characteristics of sleep, shallow torpor, and hibernation in mammals and birds and proposes that they are functionally homologous processes. In addition, the chapter describes phylogenetic and ontogenetic correlations between sleep and endothermy, and sleep-dependent thermoregulatory adjustments associated with decreased metabolism consistent with an energy conserving role for sleep.

Sleep as an Adaptation for Energy Conservation Functionally Related to Hibernation and Shallow Torpor

Slow wave sleep, shallow torpor and hibernation: Homologous states of diminished metabolism and body temperature

The hypothesis is proposed that sleep constitutes a period of dormancy in which energy is conserved to partially offset the increased energy demands of homeothermy. Phylogenetic data indicate that the complete physiological and behavioral manifestations of sleep are unique to homeotherms; furthermore “ontogeny recapitulates phylogeny” in the parallel development of slow wave sleep and thermoregulation as exemplified in the opossum. Thus, sleep constitutes a state of reduced metabolism that may represent a variation on the theme of dormancy, functionally lying on a continuum of energy conservation processes, ranging from inactivity and estivation to torpor and hibernation. The high amounts of sleep in infancy may involve conservation of energy and its consequent availability for growth. Decreased amounts of stage 4 and total sleep with aging in humans may represent reduced energy demands reflected by parallel declines in basal metabolic rate and physical activity. Disruptions of circadian rhythms of sleep and wakefulness in humans produce impairments in mood and performance independent of total amounts of sleep obtained, and reduce the amplitude of physiological rhythms. It is suggested that aging processes might also be affected by such disruptions in activity rhythms. Berger, R. J. Bioenergetic functions of sleep and activity rhythms and their possible relevance to aging. Federation Proc. 34: 97–102, 1975.

Ralph J. Berger

Papers

Energy conservation and sleep

Performance and mood following variations in the length and timing of sleep.

Sleep as an Adaptation for Energy Conservation Functionally Related to Hibernation and Shallow Torpor

Slow wave sleep, shallow torpor and hibernation: Homologous states of diminished metabolism and body temperature

Bioenergetic functions of sleep and activity rhythms and their possible relevance to aging