Consciousness is the awareness of oneself and the environment. Changing states of consciousness are often associated with biological rhythms—periodic fluctuations in physiological functioning. Circadian fluctuations occur about once a day and are governed by a biological clock in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN regulates and, in turn, is affected by the hormone melatonin, which is responsive to changes in light and dark and which increases during the dark hours. When a person's normal routine changes, the person may experience internal desynchronization, in which the usual circadian rhythms are thrown out of phase with one another.
Some people experience depression every winter in a pattern that has been labeled seasonal affective disorder (SAD). The causes of SAD, which is relatively uncommon, are not yet clear, although light treatments can be effective in alleviating symptoms. Another long-term rhythm is the menstrual cycle, during which various hormones rise and fall. Well-controlled, double-blind studies on premenstrual syndrome do not support claims that emotional symptoms are reliably and universally tied to the menstrual cycle. Expectations and learning affect how both sexes interpret bodily and emotional changes. Few people of either sex are likely to undergo dramatic monthly mood swings or personality changes because of hormones.
During sleep, periods of rapid eye movement (REM) alternate with non-REM (NREM) sleep in approximately a 90-minute rhythm. Non-REM sleep is divided into stages on the basis of characteristic brain-wave patterns. During REM sleep, the brain is active, and there are other signs of arousal, yet most of the skeletal muscles are limp; vivid dreams are reported most often during REM sleep.
Sleep is necessary not only for bodily restoration but also for normal mental functioning. Many people get less than the optimal amount of sleep, perhaps suffering from insomnia, sleep apnea, narcolepsy, or REM behavior disorder, but the most common reason for daytime sleepiness is probably a simple lack of sleep. Sleep may contribute to the consolidation of memories and subsequent problem solving. These benefits have been associated most closely with slow-wave sleep, but also with REM sleep.
Freud thought that dreams allow us to express forbidden or unrealistic desires that have been forced into the unconscious part of the mind, but there is no objective way to verify Freudian interpretations of dreams and no convincing support for most of his claims. Three modern theories of dreaming emphasize the connections between dreams and waking thoughts. The problem-focused approach holds that dreams express current concerns and may even help us solve current problems. The cognitive approach holds that dreams are simply a modification of the cognitive activity that goes on when we are awake. The difference is that during sleep we are cut off from sensory input from the world, so our thoughts tend to be more diffuse and unfocused. The activation–synthesis theory holds that dreams occur when the cortex tries to make sense of, or interpret, spontaneous neural firing initiated in the pons. The resulting synthesis of these signals with existing knowledge and memories results in a dream.
All of the current theories of dreams have some support, and all have weaknesses. Some psychologists doubt that people can solve problems during sleep. The activation–synthesis theory does not seem to explain coherent, story-like dreams or non-REM dreams. The cognitive approach is now a leading contender, although some of its specific claims remain to be tested.
Hypnosis is a procedure in which the practitioner suggests changes in a person's sensations, perceptions, thoughts, feelings, or behavior, and the person tries to comply. Although hypnosis has been used successfully for many medical and psychological purposes, people hold many misconceptions about what it can accomplish. It cannot force people to do things against their will, confer special abilities that are otherwise impossible, increase the accuracy of memory, or produce a literal re-experiencing of long-ago events.
A leading approach to understanding hypnosis is that it involves dissociation, a split in consciousness. In one version of this approach, the split is between a part of consciousness that is hypnotized and a hidden observer that watches but does not participate. In another version, the split is between an executive-control system in the brain and other brain systems responsible for thinking and acting. The sociocognitive explanationregards hypnosis as a product of normal social and cognitive processes in which the hypnotized person's expectations and beliefs combine with the desire to comply with the hypnotist's suggestions. In this view, hypnosis is a form of role-playing; the role is so engrossing that the person interprets it as real. Sociocognitive processes can account for the apparent age and past-life “regressions” of people under hypnosis and their reports of alien abductions.
In all cultures, people have found ways to produce altered states of consciousness. Psychoactive drugs alter cognition and emotion by acting on neurotransmitters in the brain. Most psychoactive drugs are classified as stimulants, depressants, opiates, or psychedelics, depending on their central nervous system effects and their impact on behavior and mood. However, some common drugs, such as marijuana, straddle or fall outside these categories.
When used frequently and in large amounts, some psychoactive drugs can damage neurons in the brain and impair learning and memory. Their use may lead to tolerance, in which increasing dosages are needed for the same effect, and withdrawal symptoms if a heavy user tries to quit. But certain drugs, such as alcohol and marijuana, are also associated with some health benefits when used in moderation.
Reactions to a psychoactive drug are influenced not only by its chemical properties but also by the user's prior experience with the drug, individual characteristics, environmental setting, and mental set—the person's expectations and motives for taking the drug. Expectations can be even more powerful than the drug itself, as shown by the “think–drink” effect.