Hockenbury Discovering Psychology 5th txtbk

146 CHAPTER 4 Consciousness and Its VariationsREM reboundA phenomenon in which a person who isdeprived of REM sleep greatly increases theamount of time spent in REM sleep at thefirst opportunity to sleep uninterrupted.Do We Need to Sleep?That we have a biological need for sleep is clearly demonstrated by sleep deprivationstudies. After being deprived of sleep for just one night, research subjects developmicrosleeps, which are episodes of sleep lasting only a few seconds that occur duringwakefulness. People who go without sleep for a day or more also experience disruptionsin mood, mental abilities, reaction time, perceptual skills, and complex motorskills (Bonnet, 2005).But what about getting less than your usual amount of sleep? Sleep restrictionstudies reduce the amount of time that people are allowed to sleep to as little as fourhours per night.Sleep restriction produces numerous impairments and changes, not the least ofwhich is an increased urge to sleep. Concentration, vigilance, reaction time, memoryskills, and the ability to gauge risks are diminished. Motor skills—including drivingskills—decrease, producing a greater risk of accidents. As discussed in the Focuson Neuroscience titled "The Sleep-Deprived Emotional Brain," moods, especiallynegative moods, become much more volatile (Dinges & others, 2005). Metabolicand hormonal disruptions occur, including harmful changes in levels of stress hormones(Van Cauter, 2005). The immune system’s effectiveness is diminished, makingthe person more susceptible to colds and infections.As sleep restriction continues for night after night, all of these changes becomemore pronounced. The problem is that most people are not good at judging the extentto which their performance is impaired by inadequate sleep. People tend tothink they are performing adequately, but in fact, their abilities and reaction timeare greatly diminished (Walker, 2008).Sleep researchers have also selectively deprived people of different components ofnormal sleep. To study the effects of REM deprivation, researchers wake sleeperswhenever the monitoring instruments indicate that they are entering REM sleep. Afterseveral nights of being selectively deprived of REM sleep, the subjects areallowed to sleep uninterrupted. What happens? They experience REM rebound—the amount of time spent in REM sleep increases by as much as 50 percent. Similarly,when people are selectively deprived of NREM stages 3 and 4, they experienceNREM rebound, spending more time in NREM sleep (Borbély & Achermann, 2005;Tobler, 2005). Thus, it seems that the brain needs to experience the full range ofsleep states, making up for missing sleep components when given the chance.FOCUS ON NEUROSCIENCEThe Sleep-Deprived Emotional BrainWhether they are children or adults, people often react withgreater emotionality when they’re not getting adequate sleep(Zohar & others, 2005). Is this because they’re simply tired, or dothe brain’s emotional centers become more reactive in responseto sleep deprivation?To study this question, researcher Seung-Schik Yoo and hiscolleagues (2007) deprived some participants of sleep for35 hours while other participants slept normally. Then, all of theparticipants observed a series of images ranging from emotionallyneutral to very unpleasant and disturbing images whileundergoing an fMRI brain scan.Compare the two fMRI scans shown here. The orange and yellowareas indicate the degree of activation in the amygdala, akey component of the brain’s emotional centers. Comparedto the adequately rested participants, the amygdala activated60 percent more strongly when the sleep-deprived participantslooked at the aversive images.Yoo’s research clearly shows that the sleep-deprived brainis much more prone to strong emotional reactions, especiallyin response to negative stimuli. So when you’re consistentlyoperating on too little sleep, monitor and gauge your emotionalreactions so you don’t overreact, only to regret it later. Better yet,get some sleep before you speak.Sleep ControlSleep Deprivation