On Sleeping and Dreaming- why do we do it?
Summary: Sleep is a natural, temporary state of reduced consciousness in which the brain remains active but less responsive to external stimuli. It protects the body, supports learning and memory, and restores energy. Sleep follows a circadian rhythm regulated by environmental cues like light and darkness.
There are two major types of sleep: NREM sleep, which includes four stages from light sleep to deep restorative sleep, and REM sleep, which features rapid eye movement and vivid dreaming. Waves in the brain shift across these stages—alpha waves in relaxed wakefulness, theta and spindles in light sleep, and slow delta waves in deep sleep. REM sleep resembles wakefulness in brain activity.
Dream theories propose various functions: Freudian theories focus on hidden wishes, activation–synthesis theory sees dreams as the brain making sense of random neural activity, and other theories suggest dreams help process daily events or rehearse responses to threats.
Sleep deprivation impairs concentration, memory, mood, and reaction time, and long-term loss can be dangerous. Many factors—illness, stress, diet, or the sleep environment—affect sleep quality.
Several sleep disorders interrupt normal sleep patterns: insomnia, narcolepsy, sleep apnea, night terrors, and sleepwalking, each with different causes and treatments.
Neurotransmitters change across sleep stages: serotonin is highest in wakefulness, GABA increases during NREM to reduce brain activity, norepinephrine decreases during REM, and acetylcholine is active when dreaming.