Chapter 3 How Does Sleep Affect Consciousness Sleep Is Part of the Normal Rhythm of Life Brain activity and other physiological processes are regulated into daily patterns known as circadian rhythms circadian roughly translates to about a day Sleep wake cycles operate according to circadian rhythms as do body temperature and hormone levels Circadian rhythms are influenced by the cycles of light and dark Even when removed from light cues however we continue to show these rhythms as do nonhuman animals Multiple brain regions are involved in producing and maintaining circadian rhythms and your sleep wake cycle This region then sends signals to a tiny structure in the endocrine system called the pineal gland The pineal gland influences the release of melatonin a hormone that travels through the bloodstream and affects various receptors in the body including some receptors in the brain Bright light reduces the production of melatonin whereas darkness triggers its release Typical indoor lighting in the evening can cause a 50 percent decrease in melatonin although people vary greatly in terms of how sensitive they are to light It is believed that melatonin helps regulate the accuracy of our biological clock Taking melatonin as a dietary supplement can help people cope with jet lag and shift work both of which interfere with circadian rhythms Taking a melatonin supplement also appears to help people fall asleep although it is unclear why this happens Four Stages of Healthy Sleep The 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 some extent however you remain aware of your surroundings and your brain still processes certain information Your mind analyzes potential dangers controls body movements and shifts body parts to maximize comfort This is why people who sleep next to children or pets tend not to roll over 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 by changes in consciousness Sleep researchers also identify the stages of sleep by other bodily processes such as rapid eye movement REM behind closed eyelids For most of the night your eyes 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 N1 sleep shown on an EEG as slower theta waves Your awareness of both the outer world and your inner mental activity starts to decline You can easily be aroused from stage N1 sleep If awakened 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 falling or that your limbs are jerking a sensation called a hypnic jerk Experts do not know exactly what causes hypnic jerks but many believe that they come from the muscles responding to brain activity 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 and your inner mental activity In this stage you are truly asleep Now the EEG shows large waves called K complexes and occasional bursts of activity called sleep spindles Abrupt noises can trigger K complexes which may be signals from brain mechanisms involved with shutting out the external world and keeping you asleep As you will learn shortly sleep spindles play an important role in memory The progression to deep sleep occurs in stage N3 sleep This period is marked by large regular delta waves and it is often called slow wave sleep People in stage N3 are very hard to wake and are often disoriented when they do wake up However people still process some outside information in this slow wave sleep because the mind continues to evaluate the 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 beta wave activity that usually represents an awake alert mind The eyes dart back and forth beneath closed 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 an active brain Indeed some regions of the brain are more active during REM sleep than during a normal waking state of consciousness But although the brain is active during REM sleep most of 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 engorgement of the clitoris REM sleep is psychologically significant because of its relation to dreaming When people are awakened during REM sleep about 80 percent of the time they report dreaming By contrast they report dreaming during non REM sleep less than half the time Solms 2000 As you will see in the next study unit you have different types of dreams during these two types of sleep Dreams are one of life s great mysteries Why do our minds create images fantasies stories that make little sense and scenes that ignore physical laws and rules of both time and space Why does the mind confuse these creations with reality Although they sometimes incorporate external sounds or other sensory experiences that happen while we sleep dreams are the products of our consciousness Have you ever woken up and had doubts about whether something happened in real life or only in your dream Our dreams feel real while we are having them Dreams also tend to be very social with just under 90 percent involving interactions with people we know with strangers and even with those who are deceased Rem Dreams and Non Rem Dreams You dream during both REM and non REM sleep But in the two types of sleep the content of your dreams differs REM dreams are more likely to be bizarre They may involve intense emotions visual and auditory hallucinations but rarely taste smell or pain and an uncritical acceptance of illogical events You fly are chased by monsters or tunnel through the center of the Earth Non REM dreams feel
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