Hockenbury Discovering Psychology 5th txtbk

140 CHAPTER 4 Consciousness and Its Variationselectroencephalograph(e-lec-tro-en-SEFF-uh-low-graph) An instrumentthat uses electrodes placed on thescalp to measure and record the brain’selectrical activity.EEG (electroencephalogram)The graphic record of brain activity producedby an electroencephalograph.What this means is that exposure to environmental time signals is necessary for usto stay precisely synchronized, or entrained, to a 24-hour day. Practically speaking,this has some important applications. For example, imagine that you leave Denver at2:00 P.M. on a 10-hour flight to London. When you arrive in London, it’s 7:00 A.M.and the sun is shining. However, your body is still on Denver time. As far as your internalbiological clock is concerned, it’s midnight.The result? Your circadian rhythms are drastically out of synchronization with daylightand darkness cues. The psychological and physiological effects of this disruptionin circadian rhythms can be severe. Thinking, concentration, and memory get fuzzy.You experience physical and mental fatigue, depression or irritability, and disruptedsleep (Eastman & others, 2005). Collectively, these symptoms are called jet lag.Although numerous physiological variables are involved in jet lag, the circadiancycle of the hormone melatonin plays a key role. When it’s 10:00 A.M. in London,it’s 3:00 A.M. in Denver. Since your body is still operating on Denver time, yourmelatonin production is peaking. Rather than feeling awake, you feel very sleepy,sluggish, and groggy. For many people, it can take a week or longer to fully adjustto such an extreme time change.SleepKey Theme• Modern sleep research began with the invention of the EEG and the discoverythat sleep is marked by distinct physiological processes and stages.Wired for Sleep Three main measurementsare recorded throughout the night in asleep lab or clinic. Using electrodes pastedto the scalp, the electroencephalogram(EEG) detects changes in the brain’s electricalactivity. The electromyogram (EMG)uses electrodes taped to the chin to recordchanges in muscle tone and chin movements.The electrooculogram (EOG) recordseyeball movements using electrodes positionednear each eye. This young woman’supper and lower limb movements, respirations,heart rate, and airflow are also beingmeasured. Although it may look uncomfortable,most people involved in sleepstudies become oblivious to the electrodesand wires as they drift into sleep(Carskadon & Rechtschaffen, 2005).Key Questions• What characterizes sleep onset, the NREM sleep stages, and REM sleep?• What is the typical progression of sleep cycles? How do sleep patternschange over the lifespan?• What evidence suggests that we have a biological need for sleep?From Aristotle to Shakespeare to Freud, history is filled with examples of scholars,writers, and scientists who have been fascinated by sleep and dreams. But prior tothe twentieth century, there was no objective way to study the internal processesthat might be occurring during sleep. Instead, sleep was largely viewed as a periodof restful inactivity in which dreams sometimes occurred.The Dawn of Modern Sleep ResearchThe invention of the electroencephalograph by German psychiatristHans Berger in the 1920s gave sleep researchers an important tool formeasuring the rhythmic electrical activity of the brain (Stern, 2001).These rhythmical patterns of electrical activity are referred to as brainwaves. The electroencephalograph produces a graphic record called anEEG, or electroencephalogram. By studying EEGs, sleep researchersfirmly established that brain-wave activity systematically changesthroughout sleep.Along with brain activity, today’s sleep researchers monitor a varietyof other physical functions during sleep. Eye movements, musclemovements, breathing rate, airflow, pulse, blood pressure, amount ofexhaled carbon dioxide, body temperature, and breathing sounds arejust some of the body’s functions that are measured in contemporarysleep research (Carskadon & Dement, 2005).