This chapter covers various aspects of consciousness, including what consciousness is thought to be, circadian rhythms, and states of altered consciousness that include sleep and dreaming, drugs, and hypnosis.

Consciousness is defined as our moment-to-moment awareness of ourselves and our environment. It is subjective, meaning that everyone's sense of reality is different. It is also private: Other people don't have direct access to your consciousness. It is dynamic or changing in that we go through different states of awareness at different times. Finally, it is self-reflective. The mind is aware of itself. Thus, consciousness is central to how we define our "selves." Freud proposed that we have a conscious mind, containing what we are currently aware of; a preconscious mind, containing things that can be brought into consciousness; and an unconscious mind, containing things that ordinarily cannot be brought into conscious awareness. Modern psychodynamic views suggest that emotional and motivational processes may operate unconsciously. Current cognitive psychologists view conscious and unconscious processes as complementary forms of information processing. People use both voluntary conscious effort, or controlled processing, and little or no conscious effort, or automatic processing, to perform various tasks. Automatic processing facilitates divided attention, enabling us to do several things at the same time. The modular mind approach suggests that various "modules," or information processing subsystems within the brain, interact to help us perform various behavioral tasks.

Circadian rhythms are our daily biological clocks and are controlled by the suprachiasmatic nuclei of the hypothalamus. These rhythmic changes in body temperature, certain hormonal secretions, and other bodily functions like sleep and waking states are on an approximately 24-hour cycle. Environmental changes such as seasons, jet lag, and night shiftwork can alter circadian rhythms. For example, seasonal affective disorder (SAD) is a cyclic tendency to become psychologically depressed during certain months of the year (usually fall or winter).

Psychologists have been very interested in the nature of the sleep cycle. EEG recordings of brain waves show that beta waves, which have high frequency and low amplitude, occur during active waking states; alpha waves occur during feelings of relaxation or drowsiness. We go through five stages of sleep. Stage 1 is a stage of light sleep from which we can easily be awakened. As sleep becomes deeper in Stage 2, sleep spindles, periodic bursts of brain wave activity, occur in the EEG patterns. Very slow and large delta waves occur in Stage 3 and in Stage 4 sleep, and then the EEG pattern changes as we go back into Stage 3 and 2 patterns. At this point in the sleep cycle, people enter rapid-eye-movement (REM) sleep. During REM sleep, physiological arousal increases to daytime levels for many people, and dreaming occurs frequently (although dreaming can also occur in non-REM stages).

The brain has no one "sleep center," but certain areas in the brain stem regulate falling asleep and REM sleep. Limbic system structures such as the amygdala are intensely active during REM sleep. Environmental factors and cultural norms also influence sleep. As we age, we sleep less and spend less time in Stages 3 and 4. REM sleep declines during infancy and early childhood and then remains fairly stable. The number of hours of sleep we need is affected by both genetic and environmental factors. Studies of sleep deprivation have shown deficits in mood and in cognitive and physical performance. Why do we sleep? The restoration model argues that sleep recharges our rundown bodies. Evolutionary/circadian sleep models suggest that sleep developed through evolutionary processes. Early humans may have performed tasks like hunting and food gathering during the day and stayed in shelter at night to avoid predators. Thus, the typical modern human sleeps at night.

There are several types of sleep disorders. Insomnia refers to chronic difficulty in falling or staying asleep. Narcoleptics suffer from extreme daytime sleepiness and sudden, uncontrollable sleep attacks. People with REM-sleep behavior disorder (REM-BD) don't experience normal REM sleep paralysis, and may kick violently or throw punches while asleep! Sleepwalkers typically walk during Stage 3 or 4 sleep; though they seem vaguely aware of their environment, they are typically unresponsive to other people. Most people have nightmares, and some, typically children, have night terrors. People with sleep apnea repeatedly stop and restart breathing during sleep.

Dreams are a source of endless curiosity for people, including psychologists, who study when and why we dream. We tend to dream during REM states and during the last few hours of sleep. We typically dream about familiar people and places. Our cultural backgrounds, life experiences, and current concerns influence the content of our dreams. Freud's psychoanalytic theory argued that dreams serve "wish fulfillment." According to activation-synthesis theory, dreams occur because the cortex is trying to make sense of random neural activity. Problem-solving models suggest that dreams help us find creative solutions to problems. Cognitive-process dream theories argue that both dreaming and waking thought are produced via the same neural processes.

Psychologists study the effects of various drugs on the brain and on behavior. Agonists are drugs that increase neurotransmitter activity, while antagonists are drugs that decrease it. When a drug is used repeatedly, people may develop a tolerance to it and suffer compensatory responses, which are opposite to the drug effects. Stopping the use of a drug produces withdrawal symptoms, during which more compensatory processes occur. Substance dependence is a maladaptive pattern of drug use (commonly called drug addiction) that significantly impairs the user's life. Depressants such as alcohol, barbiturates, and tranquilizers depress nervous system activity. Stimulants such as amphetamines, cocaine, and Ecstasy (MDMA) increase neural firing. Opiates such as heroin produce pain relief and a sense of euphoria. Hallucinogens like LSD produce hallucinations. Marijuana contains THC, which binds to receptors throughout the brain. Marijuana smoke is carcinogenic, and the drug impairs reaction time, thinking, and other skills while users are "high." Many factors, from genetic and biological ones to environmental and cultural ones, seem to determine how a given drug affects a given individual.

Hypnosis is a state of heightened suggestibility. Hypnotized people subjectively experience their actions to be involuntary, but hypnosis does not seem to involve any unique power that would get people to act against their wills. People under hypnosis sometimes perform what seem to be fantastic physical feats, but the effects may simply be placebo effects. On the other hand, hypnosis seems to increase pain tolerance and is not a placebo effect. Researchers seem to agree that hypnosis can affect amnesia, but they dispute the causes. Whether hypnosis can improve memory is highly debatable, and hypnotized subjects have been shown to remember things that did not happen (pseudomemories). Dissociation theories of memory suggest that hypnosis literally involves a dissociation of consciousness such that a person simultaneously experiences two streams of consciousness. Social-cognitive theories suggest that people are acting out the role of being hypnotized when under a hypnotic trance and thus act in ways that conform to the role of what they believe a hypnotized person can do.