Chapter 028. Sleep Disorders (Part 4)

Behavioral Correlates of Sleep States and StagesPolysomnographic staging of sleep correlates with behavioral changes during specific states and stages. During the transitional state between wakefulness and sleep (stage 1 sleep), subjects may respond to faint auditory or visual signals without "awakening."Memory incorporation is inhibited at the onset of NREM stage 1 sleep, which may explain why individuals aroused from that transitional sleep stage frequently deny having been asleep.Such transitions may intrude upon behavioral wakefulness after sleep deprivation, notwithstanding attempts to remain continuously awake (see "ShiftWork Disorder," below).Awakenings from REM sleep are associated with recall of vivid dream imagery 80%...
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Chapter 028. Sleep Disorders (Part 4) Chapter 028. Sleep Disorders (Part 4) Behavioral Correlates of Sleep States and Stages Polysomnographic staging of sleep correlates with behavioral changesduring specific states and stages. During the transitional state betweenwakefulness and sleep (stage 1 sleep), subjects may respond to faint auditory orvisual signals without awakening. Memory incorporation is inhibited at the onset of NREM stage 1 sleep,which may explain why individuals aroused from that transitional sleep stagefrequently deny having been asleep. Such transitions may intrude upon behavioral wakefulness after sleepdeprivation, notwithstanding attempts to remain continuously awake (see Shift-Work Disorder, below). Awakenings from REM sleep are associated with recall of vivid dreamimagery >80% of the time. The reliability of dream recall increases with REMsleep episodes occurring later in the night. Imagery may also be reported afterNREM sleep interruptions, though these typically lack the detail and vividness ofREM sleep dreams. The incidence of NREM sleep dream recall can be increased by selectiveREM sleep deprivation, suggesting that REM sleep and dreaming per se are notinexorably linked. Physiologic Correlates of Sleep States and Stages All major physiologic systems are influenced by sleep. Changes incardiovascular function include a decrease in blood pressure and heart rate duringNREM and particularly during slow-wave sleep. During REM sleep, phasic activity (bursts of eye movements) is associatedwith variability in both blood pressure and heart rate mediated principally by thevagus. Cardiac dysrhythmias may occur selectively during REM sleep.Respiratory function also changes. In comparison to relaxed wakefulness,respiratory rate becomes more regular during NREM sleep (especially slow-wavesleep) and tonic REM sleep and becomes very irregular during phasic REM sleep. Minute ventilation decreases in NREM sleep out of proportion to thedecrease in metabolic rate at sleep onset, resulting in a higher P CO2. Endocrine function also varies with sleep. Slow-wave sleep is associatedwith secretion of growth hormone, while sleep in general is associated withaugmented secretion of prolactin. Sleep has a complex effect on the secretion of luteinizing hormone (LH):during puberty, sleep is associated with increased LH secretion, whereas sleep inthe postpubertal female inhibits LH secretion in the early follicular phase of themenstrual cycle. Sleep onset (and probably slow-wave sleep) is associated with inhibition ofthyroid-stimulating hormone and of the adrenocorticotropic hormone–cortisolaxis, an effect that is superimposed on the prominent circadian rhythms in the twosystems. The pineal hormone melatonin is secreted predominantly at night in bothday- and night-active species, reflecting the direct modulation of pineal activity bythe circadian pacemaker through a circuitous neural pathway from the SCN to thepineal gland. Melatonin secretion is not dependent upon the occurrence of sleep,persisting in individuals kept awake at night. In addition, exogenous melatoninincreases sleepiness and increases sleep duration when administered to healthyadults attempting to sleep during daylight hours, at a time when endogenousmelatonin levels are low. The efficacy of melatonin as a sleep-promoting therapy for patients withinsomnia is currently not known. Sleep is also accompanied by alterations of thermoregulatory function.NREM sleep is associated with an attenuation of thermoregulatory responses toeither heat or cold stress, and animal studies of thermosensitive neurons in thehypothalamus document an NREM-sleep-dependent reduction of thethermoregulatory set-point. REM sleep is associated with complete absence of thermoregulatoryresponsiveness, effectively resulting in functional poikilothermy. However, thepotential adverse impact of this failure of thermoregulation is blunted by inhibitionof REM sleep by extreme ambient temperatures.