Studies utilizing rat models exposed to multiple types of stress, including footshock, immobilization demonstrated dysregulation of the HPA axis and sympathetic response systems such as those found in the locus coeruleus and adrenal medulla. These signal alterations lead to a reduction in the length and quality of sleep and maintenance of wakefulness, leading to insomnia. With that in mind, REM sleep deprivation and stress have been shown to induce changes in hormone release via the hypothalamic-pituitary-adrenal (HPA) axis as well as alterations in levels of neurotransmitters. Researchers have hypothesized that REM sleep may be an ideal period of reframing negative experiences and regulating emotional reactivity during a period when stress responses are normally quiescent. This hypothesis has been supported by studies such as one in which human participants expressed diminished negative reactions to images of fearful faces, and positive reactions to happy faces were augmented following a 90-minute nap. Īs described earlier, researchers have hypothesized many potential benefits of engaging in REM sleep and that, consequently, REM sleep rebound is an evolutionarily advantageous adaptive strategy with the inability to engage in it having potentially disastrous consequences. Several experimental studies utilizing EEG and hormonal measurements have illustrated that human and animal participants who experience sleep deprivation or significant stressors will experience increased frequency and intensity of REM sleep to compensate for said deprivation. One of these mechanisms is REM rebound, which refers to the compensatory increase of the frequency, depth, and intensity of rapid-eye-movement (REM) sleep following sleep deprivation or significant stressors. However some of the health benefits may include energy conservation, restoration, promotion of brain plasticity, modulating memory, emotion, and cognitive integration of stressors and mechanisms are in place to restore sleep homeostasis if sleep is disrupted. The true purpose of sleep is poorly understood. The maintenance of appropriate sleep architecture appears to play an important role in promoting physiological and mental health. Normally an individual will progress through a predictable cycle of stages beginning with wakefulness, then through each stage of NREM sleep before quickly reversing through the stages to enter REM sleep. These stages are primarily divided into rapid-eye-movement (REM) sleep, which is characterized by classic ocular saccadic movement and fast-wave EEG patterns reminiscent of wakefulness, and non-rapid-eye movement (NREM) which can be subdivided further into three stages each distinguished by distinct EEG wave patterns. Sleep is a state consisting of several different stages of reversible disconnection from the environment with accompanying reduced consciousness, atonia, and metabolic changes.
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