Sleep, Dreams and Psychoactive Drugs

The nightly cycle

The circadian rhythm is a roughly 24-hour clock run by the suprachiasmatic nucleus, which uses light to time the release of melatonin. Sleep itself runs in cycles of about 90 minutes:

• NREM-1 — light sleep, hypnagogic sensations of falling.
• NREM-2 — sleep spindles; roughly half the night is spent here.
• NREM-3 — deep slow-wave (delta) sleep, hardest to wake from. Sleepwalking, night terrors and bedwetting happen here.
• REM — paradoxical sleep: the brain looks awake, the eyes dart, vivid dreams occur, and the skeletal muscles are effectively paralysed.

The mix shifts across the night: NREM-3 dominates the early cycles and shrinks, while REM periods lengthen toward morning.

Why sleep, and what dreams are for

Sleep supports restoration, memory consolidation and growth-hormone release. Competing accounts of dreaming: Freud's wish fulfilment (manifest versus latent content, now little supported), information processing (dreams sort the day's memories), activation-synthesis (the cortex invents a story for random brainstem activity), and cognitive development views. Disorders: insomnia, narcolepsy (sudden REM intrusions), sleep apnea, and REM sleep behaviour disorder, where the usual paralysis fails.

Drugs at the synapse

Every psychoactive drug works at the synapse. An agonist mimics or boosts a neurotransmitter; an antagonist blocks its receptor; a reuptake inhibitor leaves the transmitter in the synapse longer.

• Depressants — alcohol, barbiturates: slow neural activity, impair judgement and inhibition.
• Stimulants — caffeine, nicotine, cocaine, amphetamines: speed it up, flooding dopamine.
• Opioids — mimic endorphins, suppressing pain and the body's own endorphin production.
• Hallucinogens — LSD, marijuana: distort perception.

Tolerance means needing more for the same effect; withdrawal is the discomfort of stopping.