States of Consciousness
What to know
Consciousness varies along a continuum from focused awareness to sleep, dreaming, hypnosis, and drug-altered states. Circadian rhythms follow roughly 24-hour cycles governed by the suprachiasmatic nucleus.
Sleep
Sleep cycles through stages: N1 (light, theta), N2 (sleep spindles, K-complexes), N3 (slow-wave delta, deep sleep), and REM (rapid eye movements, vivid dreams, muscle atonia, brain activity resembling wakefulness). REM and N3 dominate later and earlier in the night respectively. Theories: restorative (repair), adaptive/evolutionary (safety), and information-processing (memory consolidation). Common disorders: insomnia, narcolepsy (sudden REM onset), sleep apnea (breathing stops), night terrors (N3, mostly children), and REM sleep behavior disorder.
Dreams and altered states
Freud viewed dreams as wish fulfillment (manifest vs. latent content); activation-synthesis says the brain interprets random brainstem activity; cognitive views stress problem-solving. Hypnosis involves focused attention and suggestibility-evidence does not support dramatically enhanced memory. Meditation produces relaxed alertness.
Psychoactive drugs
Depressants (alcohol, barbiturates) slow CNS activity; stimulants (caffeine, cocaine, amphetamines) increase it; hallucinogens alter perception; opioids reduce pain. Tolerance (needing more), withdrawal (opposite effects on stopping), and dependence are key. Alcohol is a depressant despite its disinhibiting effects.
Traps
Questions often mislabel alcohol as a stimulant, confuse night terrors with nightmares, or claim hypnosis reliably recovers memories.
Rule of thumb
Match the stage to the marker: spindles/K-complexes = N2; delta = N3; atonia plus vivid dreams = REM.