consciousness
our awareness of ourselves and our environment.
circadian rhythm
the biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occur on a 24-hour cycle.
REM sleep
rapid eye movement sleep; a recurring sleep stage during which vivid dreams commonly occur. Also known as paradoxical sleep, because the muscles are relaxed (except for minor twitches) but other body systems are active.
alpha waves
the relatively slow brain waves of a relaxed, awake state.
sleep
periodic, natural loss of consciousness�as distinct from unconsciousness resulting from a coma, general anesthesia, or hibernation.
hallucinations
false sensory experiences, such as seeing something in the absence of an external visual stimulus.
delta waves
the large, slow brain waves associated with deep sleep.
NREM sleep
non-rapid eye movement sleep; encompasses all sleep stages except for REM sleep.
insomnia
recurring problems in falling or staying asleep.
narcolepsy
a sleep disorder characterized by uncontrollable sleep attacks. The sufferer may lapse directly into REM sleep, often at inopportune times.
sleep apnea
a sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings.
night terrors
a sleep disorder characterized by high arousal and an appearance of being terrified; unlike nightmares, night terrors occur during Stage 4 sleep, within two or three hours of falling asleep, and are seldom remembered.
dream
a sequence of images, emotions, and thoughts passing through a sleeping person's mind. Dreams are notable for their hallucinatory imagery, discontinuities, and incongruities, and for the dreamer's delusional acceptance of the content and later difficultie
manifest content
ccording to Freud, the remembered story line of a dream (as distinct from its latent, or hidden, content).
latent content
according to Freud, the underlying meaning of a dream (as distinct from its manifest content).
REM rebound
the tendency for REM sleep to increase following REM sleep deprivation (created by repeated awakenings during REM sleep).
hypnosis
a social interaction in which one person (the hypnotist) suggests to another (the subject) that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur.
posthypnotic suggestion
suggestion, made during a hypnosis session, to be carried out after the subject is no longer hypnotized; used by some clinicians to help control undesired symptoms and behaviors.
dissociation
a split in consciousness, which allows some thoughts and behaviors to occur simultaneously with others.
psychoactive drug
a chemical substance that alters perceptions and moods.
tolerance
the diminishing effect with regular use of the same dose of a drug, requiring the user to take larger and larger doses before experiencing the drug's effect.
withdrawal
the discomfort and distress that follow discontinuing the use of an addictive drug.
physical dependence
a physiological need for a drug, marked by unpleasant withdrawal symptoms when the drug is discontinued.
psychological dependence
a psychological need to use a drug, such as to relieve negative emotions.
addiction
compulsive drug craving and use, despite adverse consequences.
depressants
drugs (such as alcohol, barbiturates, and opiates) that reduce neural activity and slow body functions.
barbiturates
drugs that depress the activity of the central nervous system, reducing anxiety but impairing memory and judgment.
opiates
opium and its derivatives, such as morphine and heroin; they depress neural activity, temporarily lessening pain and anxiety.
stimulants
drugs (such as caffeine, nicotine, and the more powerful amphetamines, cocaine, and Ecstasy) that excite neural activity and speed up body functions.
amphetamines
drugs that stimulate neural activity, causing speeded-up body functions and associated energy and mood changes.
methamphetamine
a powerfully addictive drug that stimulates the central nervous system, with speeded-up body functions and associated energy and mood changes; over time, appears to reduce baseline dopamine levels.
Ecstasy (MDMA)
a synthetic stimulant and mild hallucinogen. Produces euphoria and social intimacy, but with short-term health risks and longer-term harm to serotonin-producing neurons and to mood and cognition.
hallucinogens
psychedelic ("mind-manifesting") drugs, such as LSD, that distort perceptions and evoke sensory images in the absence of sensory input.
LSD (lysergic acid diethylamide)
a powerful hallucinogenic drug; also known as acid.
near-death experience
an altered state of consciousness reported after a close brush with death (such as through cardiac arrest); often similar to drug-induced hallucinations.
THC
the major active ingredient in marijuana; triggers a variety of effects, including mild hallucinations.