Sleep and Dreams
6 Biological Bases of Behavior
STEP 4 Review the Knowledge You Need to Score High
Your finely tuned “biological clock,” controlled by the hypothalamus, systematically regulates changes in your body temperature, blood pressure, pulse, blood sugar levels, hormonal levels, and activity levels over the course of about a day. In an environment devoid of environmental cues to the length of a day, your free-running biological clock cycles approximately every 25 hours, but in a typical environment with light during the day and dark at night, cycles of changes, circadian rhythms, recur approximately every 24 hours. The forebrain, reticular formation, and thalamus are involved in the changes in wakefulness, arousal, and attention. Your physiological fluctuations are reflected in changes in your energy level, mood, performance, wakefulness, and sleep. Jet lag and night-shift work involve disruptions of circadian rhythms.
Why do you sleep? Evolutionary psychologists say that humans evolved a unique waking—sleeping cycle as a result of natural selection that maximized our chances of survival. Sleep serves at least two restorative functions—one involved in protein synthesis throughout the body, the other involved in maintaining plasticity of neural connections essential for storing and retrieving memories, which enables you to put together new material from the day before with old material. This is sometimes called consolidation. Sleep deprivation makes you drowsy, unable to concentrate, and impairs your memory and immune system. Sleep time seems to decrease from about 16 to 18 hours for a newborn, to about 7 to 8 hours for an adult.
Sleep is a complex combination of states of consciousness, each with its own level of consciousness, awareness, responsiveness, and physiological arousal. The amount we sleep changes as we age. Electroencephalograms (EEGs) can be recorded with electrodes on the surface of the skull. EEGs have revealed that brain waves change in form systematically throughout the sleep cycle (see Figures 6.5 and 6.6). When you are awake, your EEG shows beta waves when you are alert and alpha waves when you are relaxed. As you fall asleep, you pass into a semiwakeful state of dreamlike awareness, known as the hypnagogic state; you feel relaxed, fail to respond to outside stimuli, and begin the first stage of sleep, Non-REM-1. EEGs of NREM-1 sleep show theta waves, which are higher in amplitude and lower in frequency than alpha waves. As you pass into NREM-2, your EEG shows high-frequency bursts of brain activity (called sleep spindles) and K complexes. As you fall more deeply asleep, your NREM-3 sleep EEG shows very high amplitude and very low-frequency delta waves. In this stage, EEGs show mostly delta waves. Your heart rate, respiration, temperature, and blood flow to your brain are reduced. You secrete growth hormone involved in maintaining your physiological functions. Non-REM-3 was originally split into two stages, 3 and 4. After passing through stages 1 through 4, you pass back through stages 3, 2, and 1; then, rather than awaking, you begin REM sleep (Rapid Eye Movement sleep) about 90 minutes after falling asleep. Your eyes jerk rapidly in various directions; your breathing becomes more rapid, irregular, and shallow; your heart rate increases; your blood pressure rises; and your limb muscles become temporarily paralyzed. Because your EEG shows beta activity typical of wakefulness and theta activity typical of NREM-1 sleep, but you are truly asleep, REM sleep is often also called paradoxical sleep. Throughout the night, you cycle through the sleep stages with REM sleep periods increasing in length and deep sleep decreasing. About 50 percent of our sleep is in NREM-2. More of a newborn’s sleep is spent in REM sleep than an adult’s. Nightmares are frightening dreams that occur during REM sleep. Most of your dreaming takes place during REM sleep. Dreams remembered from other stages are less elaborate and emotional. Training in lucid dreaming, the ability to be aware of and direct one’s dreams, has been used to help people make recurrent nightmares less frightening.
Figure 6.5 Electroencephalograms of Human Sleep Stages.
Figure 6.6 Sleep Stages During a Typical Night.
“Remember delta and deep. Deep waves on the beach are high, so they have a high amplitude. Stages 3 and 4 are the highest numbers for sleep stages.”
—Lori, AP student
Interpretation of Dreams
But what do dreams mean? Psychoanalyst Sigmund Freud thought dreams were “the royal road to the unconscious,” a safety valve for unconscious desires, that reveal secrets of the unconscious part of the mind unknown to the conscious mind. Freud tried to analyze dreams to uncover the unconscious desires (many of them sexual) and fears disguised in dreams. He considered the remembered story line of a dream its manifest content, and the underlying meaning its latent content. Psychiatrists Robert McCarley and J. Alan Hobson proposed another theory of dreams called the activation-synthesis theory. During a dream, the pons generates bursts of action potentials to the forebrain, which is activation. The dreamer then tries to make sense of the stimulation by creating a story line, which is synthesis. The origin of dreams is psychological according to psychoanalysts and physiological according to McCarley and Hobson. A cognitive view holds that when we sleep, information from the external world is largely cut off. So the only world our constantly active brain can model is the one already inside it from stored memories, recent concerns, current emotions, and expectations, which can be activated by electrical impulses discharged from within the brain. In other words, dreams are the interplay of the physiological triggering of brain waves and the psychological functioning of the imaginative, interpretive parts of the mind. Recent studies indicate correspondences between what you do in the dream state and what happens to your physical body and brain. Thus, if you dream you’re doing something, to your brain, it’s as if you’re actually doing it.
Chances are you’ve been sleep deprived at one time or another. When you get little or no sleep one night, you spend more of your sleep time the next night in REM sleep (called REM rebound), with few consequences. But millions of people suffer from chronic, long-term sleep disorders. The most common adult sleep disorders include insomnia, sleep apnea, and narcolepsy, while children are more likely to experience night terrors and sleepwalking. Insomnia is the inability to fall asleep and/or stay asleep. Insomnia complainers typically overestimate how long it takes them to fall asleep and underestimate how long they stay asleep. Sleep researchers recommend that you go to bed at a set time each night and get up at the same time each morning; exercise for about a half hour daily 5 or 6 hours before going to bed; avoid alcohol, sleeping pills, and stimulants; avoid stress; and relax before bed to avoid insomnia. Narcolepsy is a condition in which an awake person suddenly and uncontrollably falls asleep, often directly into REM sleep. Victims often benefit from naps or drug therapy with stimulants or antidepressants. Sleep apnea is a sleep disorder characterized by temporary cessations of breathing that awaken the sufferer repeatedly during the night. Sleep apnea most often results from obstruction or collapse of air passages, which occurs more frequently in obese people. Weight loss and sleeping on the side can help alleviate the problem. An effective treatment is a positive pressure pump that provides a steady flow of air through a face mask worn by the sufferer. Night terrors are most frequently childhood sleep disruptions from the deepest part of NREM-3 (formerly referred to as stage 4) sleep characterized by a bloodcurdling scream and intense fear. Sleepwalking, also called somnambulism, is also most frequently a childhood sleep disruption that occurs during deep NREM-3 sleep characterized by trips out of bed or carrying on of complex activities. Typically, sufferers do not recall anything in the morning.