Hockenbury Discovering Psychology 5th txtbk

Sleep145AwakeNREM stage12Sleep position shiftsREM REM REM REM REMAwake12Figure 4.3 The 90-Minute Cycles ofSleep During a typical night, you experiencefive 90-minute cycles of alternatingNREM and REM sleep. The deepeststages of NREM sleep, stages 3 and 4,occur during the first two 90-minutecycles. Dreaming REM sleep episodesbecome progressively longer as thenight goes on. Sleep position shifts, indicatedby the dots, usually occur immediatelybefore and after REMepisodes.Source: Based on Hobson (2004).334411 PM 12 AM 1 AM 2 AM 3 AM 4 AM 5 AM 6 AM 7 AMTimeFrom childhood through lateadulthood, the pattern of a typicalnight’s sleep evolves and changes(see Figure 4.4). Total sleep timeand the percentage of a night’s sleepspent in deeper slow-wave sleep decrease.This is offset by gradual increasesin the percentage of timespent each night in lighter NREMstages 1 and 2. The percentage of anight’s sleep devoted to REM sleepincreases during childhood and adolescence,remains stable throughoutadulthood, and then decreases duringlate adulthood (Ohayon & others,2004).Sleep-Deprived AdolescentsTeenagers require about 8.5 to 9hours of sleep each night to be fullyrested. However, only 1 out of 7 U.S.teens actually gets that much sleep.Most adolescents report gettingaround 7 to 7.5 hours of sleep onschool nights, which is probably whythey sleep about 2 hours longer onweekends. Consequences of regularsleep loss include poor school performance,increased risk of accidentsand injuries, and depressed mood(National Sleep Foundation, 2000).600500Sleep latency400WASOREM300SWS200Stage 2100Stage 105 10 15 25 35 45 55 65Age7585Figure 4.4 Sleep over the Lifespan Sleepquality changes significantly over the lifespan.In particular, notice that slow-wavesleep decreases over the lifespan, as doestotal sleep time. By middle adulthood,people are more likely to experiencewakefulness after sleep onset, abbreviatedWASO. Senior adults aged 55 and olderoften take longer to fall asleep, which istechnically called sleep latency. Manysenior adults spend an hour or more eachnight simply dozing or resting quietlyin bed.