Hockenbury Discovering Psychology 5th txtbk

Sleep141Today, sleep researchers distinguish between two basic types of sleep. REM sleepis often called active sleep or paradoxical sleep because it is associated with heightenedbody and brain activity during which dreaming consistently occurs. NREMsleep, or non-rapid-eye-movement sleep, is often referred to as quiet sleep because thebody’s physiological functions and brain activity slow down during this period ofslumber. Usually pronounced as “Non-REM sleep,” it is further divided into fourstages, as we’ll describe shortly.The Onset of Sleep and Hypnagogic HallucinationsAwake and reasonably alert as you prepare for bed, your brain generates small, fastbrain waves, called beta brain waves. After your head hits the pillow and you closeyour eyes, your muscles relax. Your brain’s electrical activity gradually gears down,generating slightly larger and slower alpha brain waves. As drowsiness sets in, yourthoughts may wander and become less logical.During this drowsy, presleepphase, you may experience oddbut vividly realistic sensations. Youmay hear your name called or aloud crash, feel as if you’re falling,floating, or flying, or see kaleidoscopicpatterns or an unfoldinglandscape. These brief, vivid sensoryphenomena that occasionallyoccur during the transition tolight sleep are called hypnagogichallucinations. Some hypnagogicGARFIELDhallucinations can be so vivid or startling that they cause a sudden awakening(Vaughn & D’Cruz, 2005).Probably the most common hypnagogic hallucination is the vivid sensation offalling. The sensation of falling is often accompanied by a myoclonic jerk—an involuntarymuscle spasm of the whole body that jolts the person completely awake(Cooper, 1994). Also known as sleep starts, these experiences can seem really weird(or embarrassing) when they occur. But you can rest assured because hypnagogichallucinations and sleep starts are normal—if not completely understood—eventsthat sometimes occur during sleep onset (Mahowald, 2005).The First 90 Minutes of Sleep and BeyondThe course of a normal night’s sleep follows a relatively consistent cyclical pattern.As you drift off to sleep, you enter NREM sleep and begin a progression throughthe four NREM sleep stages (see Figure 4.2 on the next page). Each progressiveNREM sleep stage is characterized by corresponding decreases in brain and bodyactivity. On average, the progression through the first four stages of NREM sleepoccupies the first 50 to 70 minutes of sleep.Stage 1 NREMAs the alpha brain waves of drowsiness are replaced by even slower theta brainwaves, you enter the first stage of sleep. Lasting only a few minutes, stage 1 is a transitionalstage during which you gradually disengage from the sensations of the surroundingworld. Familiar sounds, such as the hum of the refrigerator or the soundof traffic, gradually fade from conscious awareness. During stage 1 NREM, you canquickly regain conscious alertness if needed. Although hypnagogic experiences canoccur in stage 1, less vivid mental imagery is common, such as imagining yourselfengaged in some everyday activity. These imaginations lack the unfolding, storylikedetails of a true dream.Jim DavisREM sleepType of sleep during which rapid eye movements(REM) and dreaming usually occurand voluntary muscle activity is suppressed;also called active sleep or paradoxical sleep.NREM sleepQuiet, typically dreamless sleep in whichrapid eye movements are absent; dividedinto four stages; also called quiet sleep.beta brain wavesBrain-wave pattern associated with alertwakefulness.alpha brain wavesBrain-wave pattern associated with relaxedwakefulness and drowsiness.hypnagogic hallucinations(hip-na-GAH-jick) Vivid sensory phenomenathat occur during the onset of sleep.GARFIELD © 1989 PAWS INC. Reprinted withpermission of UNIVERSAL PRESS SYNDICATE.All rights reserved.