The Mystery of Sleep Function: Current Perspectives and Future Directions

Department of Neuroscience, University ofPennsylvania, Philadelphia, PA 19014 , USA.
Reviews in the neurosciences (Impact Factor: 3.33). 02/2006; 17(4):375-92. DOI: 10.1515/revneuro.2006.17.4.375
Source: PubMed


The function of sleep is one of the most persistent and perplexing mysteries in biology. Many theories have been proposed to explain why we sleep, but most account for only a portion of sleep behavior and very few enjoy strong experimental support. A critical review of current findings leads to the following conclusions. Sleep is for the brain rather than the body, and the neural process most impacted by sleep is cognition. Sleep may influence cognition in many ways, including the removal of a toxic byproduct of wakefulness, or the restoration of neural substrates needed for mental processes. The evidence for these possibilities, however, is weak or equivocal. On the other hand, converging lines of evidence support the hypothesis that sleep promotes brain plasticity.

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Available from: Marcos G Frank, Apr 05, 2014
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    • "Data are presented as mean ± SD. immediate post-game recovery intervention utilised in this study may be the most important aspect in psychophysiological player recovery; however, this cannot be definitively shown because there were no players who did not complete the post-game intervention . This is accomplished through hydrostatic pressure (Wilcock, Cronin, & Hing, 2006) and vasoconstriction that aids in metabolite removal, a reduction in swelling and muscle soreness (Cochrane, 2004), increase in protein synthesis and restoration of the immune, endocrine and nervous systems (Frank, 2006; Howarth, Moreau, Phillips, & Gibala, 2009; Swenson, Swärd, & Karlsson, 1996). The individual difference among the subject's response to the game and protocol provides evidence of variation. "
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    ABSTRACT: Rugby union is a physical demanding sport that requires optimum recovery between games to maintain performance levels. Analysis of four unique biochemical markers of stress is measured here to determine which recovery strategy currently in use by a professional team provides the necessary requirements for sustained performance. Urine and saliva samples were collected from 37 professional rugby players before, immediately after and 36 hours after five home games, and analysed by enzyme linked immunosorbent assay and high performance liquid chromatography for urinary myoglobin, total neopterin (NP; NP + 7,8-dihydroneopterin), salivary cortisol and immunoglobulin A. Subjects completed a cold water immersion (CWI) or pool session (PS), donned compression garments, consumed protein and carbohydrate food and fluid, and slept for 8 hours post-game. The following day subjects choose from one or a combination of CWI, PS or active recovery/stretching to complete. There was no difference between the recovery protocols for cortisol, total NP, immunoglobulin A concentration or myoglobin at 36 hours post-game. Immunoglobulin A secretion rate significantly increased above pre-game levels at 36 hours post-game for all protocols; however, protocol three did not increase as much (p = 0.038). Total NP was also significantly increased above pre-game levels at 36 hours post-game for all protocols. This study provides evidence that the immediate post-game recovery intervention following a game of professional rugby union may be the most important aspect of psychophysiological player recovery, irrespective of the "next-day" intervention. The concentrations of total NP and immunoglobulin A suggest these professional rugby players are still in a state of recovery 36 hours post-game.
    04/2015; 15(6):1-7. DOI:10.1080/17461391.2015.1029982
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    • "Previous studies have established a correlation between neural restoration and sleep regularity. Other forms of restoration in the body also have been observed, but much less evidence supports the notion that sleep provides primarily somatic as opposed to neural restoration [1]. A growing consensus suggests that a major benefit of sleep involves ongoing support for neuronal function in the brain. "
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    ABSTRACT: Although sleep physiology has been extensively studied, many of the cellular processes that occur during sleep and the functional significance of sleep remain unclear. The degree of cardiorespiratory synchronization during sleep increases during the progression of slow-wave sleep (SWS). Autonomic nervous system (ANS) activity also assumes a pattern that correlates with the progression of sleep. The ANS is an integral part of physiologic processes that occur during sleep with the respective contribution of parasympathetic and sympathetic activity varying between different sleep stages. In our paper, we attempt to unify the activities of various physiologic systems, namely the cardiac, respiratory, ANS and brain, during sleep into a consolidated picture with particular attention to the membrane potential of neurons. In our unified model, we explore the potential of sleep to promote restorative processes in the brain.
    Sleep Medicine 03/2014; 15(3). DOI:10.1016/j.sleep.2013.10.017 · 3.15 Impact Factor
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    • "Sleep is a complex physiological process and still remains one of the great mysteries of science [1] [2]. Hypotheses for the function of sleep include somatic, metabolic and cellular theories, as well as brain-specific alterations affecting synaptic plasticity and leading to synaptic downscaling [3e10]. "
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    ABSTRACT: Sleep is a complex physiological process and still remains one of the great mysteries of science. Over the past 10 y, genetic research has provided a new avenue to address the regulation and function of sleep. Gene loci that contribute quantitatively to sleep characteristics and variability have already been identified. However, up to now, a genetic basis has been established only for a few sleep disorders. Little is yet known about the genetic background of insomnia, one of the most common sleep disorders. According to the conceptualisation of the 3P model of insomnia, predisposing, precipitating and perpetuating factors contribute to the development and maintenance of insomnia. Growing evidence from studies of predisposing factors suggests a certain degree of heritability for insomnia and for a reactivity of sleep patterns to stressful events, explaining the emergence of insomnia in response to stressful life events. While a genetic susceptibility may modulate the impact of stress on the brain, this finding does not provide us with a complete understanding of the capacity of stress to produce long-lasting perturbations of brain and behaviour. Epigenetic gene-environment interactions have been identified just recently and may provide a more complex understanding of the genetic control of sleep and its disorders. It was recently hypothesised that stress-response-related brain plasticity might be epigenetically controlled and, moreover, several epigenetic mechanisms have been assumed to be involved in the regulation of sleep. Hence, it might be postulated that insomnia may be influenced by an epigenetic control process of both sleep mechanisms and stress-response-related gene-environment interactions having an impact on brain plasticity. This paper reviews the evidence for the genetic basis of insomnia and recent theories about epigenetic mechanisms involved in both sleep regulation and brain-stress response, leading to the hypothesis of an involvement of epigenetic mechanisms in the development and maintenance of insomnia.
    Sleep Medicine Reviews 08/2013; 18(3). DOI:10.1016/j.smrv.2013.05.002 · 8.51 Impact Factor
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