• Consciousness is the awareness people have of themselves and the environment around them.
  • The level and state of consciousness vary. Different states of consciousness are associated with different brain wave patterns. Brain waves are tracings that show the kind of electrical activity going on in the brain. Scientists use an electroencephalograph, or EEG, to record these waves.
  • The main types of brain waves are alpha, beta, theta, and delta.


  • Types of biological rhythms include circadian, infradian, and ultradian rhythms.
  • Endogenous biological rhythms originate from inside the body rather than from the outside environment.
  • Biological clocks in the body regulate the sense of time.
  • The suprachiasmatic nucleus regulates circadian rhythms of sleep.
  • Different theories suggest that people sleep to conserve energy, stay safe from predators, or restore body tissues depleted during the day.
  • Researchers use EEGs, EMGs, EOGs, and EKGs to record sleep patterns.
  • There are five stages of sleep. At each stage, different types of brain waves function, and heart rate, breathing, and temperature vary.
  • During REM sleep, heart rate and breathing become irregular, eyes move rapidly, and muscles relax. Dreams are most vivid during REM sleep.
  • Sleep patterns change as people age, with most people needing less sleep as they get older.
  • Sleep disorders include insomnia, narcolepsy, and sleep apnea.


  • Sigmund Freud believed that dreams allow people to express unconscious wishes. He said the manifest content of dreams, or the dream’s plot, symbolizes the latent content, or hidden meaning.
  • The activation-synthesis theory proposes that neurons in the brain randomly activate during REM sleep. Dreams arise when the cortex tries to make sense of these impulses.
  • Some researchers think dreams express people’s most pressing concerns, while others think dreams arise during the brain’s routine housekeeping chores such as eliminating or strengthening neural connections.

Altered States

  • Altered states are induced states of consciousness and include hypnotic states, meditative states, and drug-induced states.
  • In hypnosis, a hypnotist makes suggestions to a person. One theory states that people in hypnosis divide their consciousness into two parts. Other theories say that people merely play a role when hypnotized.
  • Meditation is the practice of focusing attention.
  • Psychoactive drugs are usually used for recreational rather than medical purposes, though some have legitimate medical uses. These drugs change sensory experience, perception, mood, thinking, and behavior.
  • Recreational drugs include stimulants, sedatives, narcotics, and hallucinogens.
  • Drugs work by affecting neurotransmitter function in various ways.
  • The effect of any drug depends on many factors such as the amount of the drug, how the drug is administered, and the user’s mood, personality, and motivation.
  • Chronic use of drugs can result in tolerance, withdrawal symptoms, physical dependence, or psychological dependence.
  • Drug use can be dangerous.

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