Chapter 3: How Does Sleep Affect Consciousness?Sleep Is Part of the Normal Rhythm of LifeBrain activity and other physiological processes are regulated into daily patterns known ascircadian rhythms (circadian roughly translates to "about a day"). Sleep/wake cycles operateaccording to circadian rhythms, as do body temperature and hormone levels. Circadian rhythmsare influenced by the cycles of light and dark. Even when removed from light cues, however, wecontinue to show these rhythms, as do nonhuman animals. Multiple brain regions are involved inproducing and maintaining circadian rhythms and your sleep/wake cycle. This region then sendssignals to a tiny structure in the endocrine system called the pineal gland. The pineal glandinfluences the release of melatonin, a hormone that travels through the bloodstream and affectsvarious receptors in the body, including some receptors in the brain. Bright light reduces theproduction of melatonin, whereas darkness triggers its release. Typical indoor lighting in theevening can cause a 50 percent decrease in melatonin, although people vary greatly in terms ofhow sensitive they are to light. It is believed that melatonin helps regulate the accuracy of ourbiological clock. Taking melatonin as a dietary supplement can help people cope with jet lag andshift work, both of which interfere with circadian rhythms. Taking a melatonin supplement alsoappears to help people fall asleep, although it is unclear why this happens.Four Stages of Healthy SleepThe difference has as much to do with conscious experience as with biological processes.When you sleep, your conscious experience of the outside world is largely turned off. To someextent, however, you remain aware of your surroundings, and your brain still processes certaininformation. Your mind analyzes potential dangers, controls body movements, and shifts bodyparts to maximize comfort. This is why people who sleep next to children or pets tend not to rollover onto them and why, after infancy, most people do not fall out of bed while sleeping.As EEG readings indicate, sleep typically occurs in four stages. These stages are marked bychanges in consciousness. Sleep researchers also identify the stages of sleep by other bodilyprocesses, such as rapid eye movement (REM) behind closed eyelids. For most of the night, youreyes do not engage in rapid eye movements, and so this type of sleep is called non-REM(NREM) sleep. When you start to drift off, you enter the first NREM phase of sleep, stage N1sleep, shown on an EEG as slower theta waves. Your awareness of both the outer world and yourinner mental activity starts to decline. You can easily be aroused from stage N1 sleep. Ifawakened, you probably won't be aware that you were drifting off. In this stage before true sleep,you might see fantastical images or geometric shapes. Or you might have the sensation of fallingor that your limbs are jerking, a sensation called a hypnic jerk. Experts do not know exactlywhat causes hypnic jerks, but many believe that they come from the muscles responding to brainactivity that occurs in stage N1 sleep. Because these jerks shift us briefly out of stage N1 sleep,we become aware that we just moved. This conscious awareness usually does not last long,though. It fades when we slip back into sleep for the night. As you progress to stage N2 sleep,your breathing becomes more regular, and you become even less aware of the outside world andyour inner mental activity. In this stage, you are truly asleep. Now the EEG shows large wavescalled K-complexes and occasional bursts of activity called sleep spindles. Abrupt noises cantrigger K-complexes, which may be signals from brain mechanisms involved with shutting outthe external world and keeping you asleep. As you will learn shortly, sleep spindles play animportant role in memory. The progression to deep sleep occurs in stage N3 sleep. This period ismarked by large, regular delta waves, and it is often called slow-wave sleep. People in stage N3are very hard to wake and are often disoriented when they do wake up. However, people stillprocess some outside information in this slow-wave sleep because the mind continues to evaluatethe environment for potential danger. After about 90 minutes of sleep, the sleep cycle reverses,eventually returning to stage N1 sleep. At this point, the EEG suddenly shows a flurry of betawave activity that usually represents an awake, alert mind. The eyes dart back and forth beneathclosed eyelids. Because of these rapid eye movements, this stage is called stage R or REM sleep. It is sometimes called paradoxical sleep because of the paradox of a sleeping body with anactive brain. Indeed, some regions of the brain are more active during REM sleep than during anormal waking state of consciousness. But although the brain is active during REM sleep, mostof the body's muscles are paralyzed. At the same time, the body shows signs of genital arousal:Most males of all ages develop erections, and most females of all ages experience engorgementof the clitoris.REM sleep is psychologically significant because of its relation to dreaming. Whenpeople are awakened during REM sleep, about 80 percent of the time they report dreaming. Bycontrast, they report dreaming during non-REM sleep less than half the time (Solms, 2000). Asyou will see in the next study unit, you have different types of dreams during these two types ofsleep.Dreams are one of life's great mysteries. Why do our minds create images, fantasies, stories thatmake little sense, and scenes that ignore physical laws and rules of both time and space? Whydoes the mind confuse these creations with reality? Although they sometimes incorporateexternal sounds or other sensory experiences that happen while we sleep, dreams are theproducts of our consciousness. Have you ever woken up and had doubts about whethersomething happened in real life or only in your dream? Our dreams feel real while we are havingthem. Dreams also tend to be very social, with just under 90 percent involving interactions withpeople we know, with strangers, and even with those who are deceasedRem Dreams and Non-Rem DreamsYou dream during both REM and non-REM sleep. But in the two types of sleep, the content ofyour dreams differs. REM dreams are more likely to be bizarre. They may involve intenseemotions, visual and auditory hallucinations (but rarely taste, smell, or pain), and an uncriticalacceptance of illogical events. You fly, are chased by
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