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Chapter Summary from Current Diagnosis & Treatment
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For a clinical review of the topic in Current Diagnosis & Treatment, 3e please go to Chapter 4: Coma, Chapter 31: Sleep Disorders.
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SLEEP IS A REMARKABLE STATE. It consumes fully a third of our lives—approximately 25 years in the average lifetime—yet we know little about what happens in the brain during this daily excursion. Perhaps even more surprising, the exact functions of sleep and of dreaming, one of the more noteworthy components of sleep, are still unknown.
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Although the psychological content of dreams has been a rich subject of speculation from Plato and Aristotle to Sigmund Freud, we still do not understand whether dreams carry deep personal meaning, as Freud hypothesized, or represent the brain “throwing out its trash,” the bits and pieces of daily experience that are not worth retaining, as Francis Crick speculated. One function of sleep may be to allow synaptic remodeling and consolidation of memory traces reflecting the day’s experiences, but the role of dreaming in this process remains a subject of intense debate.
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When studying sleep and wakefulness, researchers typically use a polysomnogram, which consists of three physiological measures: brain activity measured by an electroencephalogram (EEG) (see Figure 58–1), eye movements recorded by an electro-oculogram (EOG), and muscle tone measured by an electromyogram (EMG) (Figure 44–1B). In clinical polysomnograms, respiration is also measured, as breathing during sleep is disrupted in many patients with sleep disorders.
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