Ralph J. Berger

Energy conservation and sleep

Phylogenetic and ontogenetic associations between sleep and endothermy are consistent with the hypothesis that sleep evolved in conjunction with endothermy to offset the high energetic cost of endothermy. The electrophysiological and thermoregulatory continuum of slow wave sleep, circadian torpor and hibernation substantiates a primordial link between sleep and energy conservation. Sleep constitutes a circadian and circannual rhythm of hypometabolic adaptation to biospheric energy cycles that is usually entrained through light-mediated suppression of melatonin secretion. When energy stores decline, energy is conserved by lowering Tb proportionally during sleep or by increasing the daily duration of sleep.

Sleep as an adaptation for energy conservation functionally related to hibernation and shallow torpor.

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.

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

Until recently, sleep and hibernation were not usually considered to be closely related states (e.g. Dement, 1967). However, two current lines of research point toward a system of relations between caloric intake, thermogenesis, metabolic rate and adiposity in the regulation of the energy balance of warm-blooded animals (endotherms). One line indicates that sleep, shallow torpor and hibernation are homologous energy conserving processes, lying on a continuum of decreasing metabolism and body temperature (Tb). The other line indicates that the metabolic reductions brought about by sleep, shallow torpor and hibernation are regulated in accordance with periodic ecological factors affecting energy intake and energy balance.

The effects of changing the phase and duration of sleep.

The relative effects of extended sleep, reduced sleep, and shifts of habitual sleep time on subsequent performance and mood were studied. Ten healthy male university students who regularly sleep 9.5-10.5 hr were the subjects. Measurements were obtained from a 45-min auditory vigilance task, a 5-min experimenter-paced addition task and a mood adjective check list 30 min after awakening, at midday, and in the evening following five electroencephalographically recorded nights of sleep. The experimental treatments compromised at 9.5-10.5 hr habitual sleep condition and four conditions in which the regular sleep period was lengthened, reduced, delayed, and advanced by 3hr. Following each 3-hr altered condition of sleep there was an equivalent decline in vigilance performance and in subjective arousal as measured by the mood scales. Together with other recent evidence, the present results support the hypothesis that acute disruption of the 24-hr sleep-wakefulness cycle produces degradations in human performance largely independent of total sleep time.

Acute shifts in the sleep-wakefulness cycle: effects on performance and mood.

&NA; Ten regular 12‐8 a.m. 8‐hour sleepers performed a 5‐min experimenter‐paced calculation task, a 30‐min vigilance task and completed an adjective check list to rate their mood following a 12‐8 a.m. habitual sleep condition and 8 p.m.‐4 a.m., 10 p.m.‐6 a.m., 2‐10 a.m., and 4 a.m.‐12 p.m. conditions of shifted sleep. After the shifted sleep conditions compared to the 12‐8 a.m. condition performance on the vigilance and calculation tasks was significantly impaired, and negative affect was significantly greater as measured by three scales of the adjective check list. Sleep length did not differ between the various conditions and the decrements in performance and mood were unrelated to any specific changes in the electrophysiological patterns of sleep.

Sleep stage patterns associated with acute shifts in the sleep-wakefulness cycle

Abstract The effect on sleep patterns of changes in length of time awake and time of sleep onset was studied by shifting the time when habitual 12-8 a.m. sleepers took their usual 8 h of sleep. Sleep stage patterns in ten male subjects were analyzed following a 12-8 a.m. habitual sleep condition and 8 p.m.–4 a.m., 10 p.m.–6 a.m., 2–10 a.m., and 4 a.m.–12 p.m. conditions of shifted sleep. As sleep occurred progressively later from 8 p.m. to 4 a.m. stage 4 significantly increased, but predominated during the first third of sleep in all conditions; REM sleep also increased significantly and the length of the REM cycle significantly decreased. Compared to the habitual sleep condition REM latency was significantly reduced in the 4 a.m.–12 p.m. condition. Total time spent asleep did not significantly differ between conditions and averaged at least 7 h. The results indicate that both the quantity and cyclic period of REM sleep exhibit a circadian rhythm, whereas the propensity for stage 4 is primarily determined by prior length of time awake.

Sleep in the domestic pigeon (Columba livia).

Abstract The EEG, EOG, neck EMG and head movements were recorded and behavioral observations made during undisturbed sleep and wakefulness in three domestic pigeons ( Columba livia ). Three states of sleep and wakefulness were distinguished: (a) Wakefulness, characterized by behavioral activity, a low voltage-high frequency EEG, ocular movements and high tonic neck EMG activity. (b) Slow-wave sleep, characterized by behavioral inactivity, high voltage slow EEG activity, and reduced tonic neck activity. (c) REM sleep, characterized by successive downward and rotational jerks of the head, a low voltage-high frequency EEG, clusters of 3-8 eye movements and a marginal but inconsistent decrease in EMG activity. REMs persisted when the pigeons head was immobilized. Forty-two percent of the 24-hr period was spent asleep. REM sleep episodes had a mean duration of 11 sec and constituted 7% of total sleep time and 3% of the 24-hr period.

Correlations between body temperatures, metabolic rate and slow wave sleep in humans

Amounts of slow wave sleep (SWS) in men exposed to either thermoneutral (29 degrees C) or cool (21 degrees C) ambient temperatures were positively correlated with tympanic and rectal temperatures at SWS onset. Decreases in each temperature measure between sleep onset and the nightly termination of SWS were negatively correlated with oxygen consumption during SWS.

Sleep in the burrowing owl (Speotyto cunicularia hypugaea)

Three distinct states of sleep and wakefulness were discriminated in burrowing owls (Speotyto cunicularia): (a) wakefulness, characterized by behavioral activity, a low voltage-high frequency electroencephalogram (EEG), and high tonic neck electromyogram (EMG); (b) slow-wave sleep, characterized by behavioral inactivity, high voltage-slow EEG activity, and a reduced tonic neck EMG; and (c) desynchronized sleep, characterized by a low voltage-high frequency EEG and neck EMG activity maintained at the same level as during prior slow-wave sleep. Phasic eye muscle activity never occurred during desynchronized sleep independently of eyelid movement. Sleep occupied 60% of the 24-hr period. Desynchronized sleep episodes had a mean duration of 11 sec, and constituted 5% of total sleep-time. The absence of EMG hypotonia of the neck and of phasic eye muscle activity, typical of other birds during desynchronized sleep, lends support to the hypothesis that the evolution of REM sleep might be linked with that of binocularly coordinated eye movement, since the eyes of the owl are immobile.

Sleep during Transcendental Meditation

Electroencephalograms (EEGs) and DC electrooculograms (EOGs) were recorded during Transcendental Meditation periods for 8 experienced Ss. The records, scored blind showed that all but 2 Ss spent considerable portions of their meditation periods in unambiguous physiological sleep.