Sleep Science
How sleep actually works — architecture, cycles, hormones, deep sleep, REM.
What deep sleep actually does for your brain
Deep sleep — the slow-wave stage in the first half of the night — is when your brain runs a cleaning cycle that may help clear waste linked to long-term brain health. It's also the stage your body protects most fiercely after sleep loss.
The 90-minute sleep cycle, explained
A normal night of sleep is built from four to six cycles of about 90 minutes. Each cycle moves through light, deep, and dream sleep — but the mix shifts as the night goes on, which explains why early morning awakenings feel different from middle-of-the-night ones.
Why your body cools down before sleep
Your body temperature follows a daily rhythm tied directly to sleep. The drop in core temperature in the evening is one of the strongest biological signals that it's time to sleep — and the room you sleep in either helps or fights it.
How sleep changes after age 40
Around middle age, sleep becomes lighter, briefer, and more interrupted. Understanding which changes are normal aging and which are insomnia can take a lot of the worry out of the night.
REM sleep: what's happening when you dream
REM is the dream stage of sleep — and one of the strangest states the brain produces. It's central to memory, learning, and emotional processing, and its rhythms across the night explain a lot of what people find odd about their own sleep.
Why do boring lectures make you sleepy?
A flat, predictable lecture gives attention little to hold onto. The same low-arousal ingredients can make bedtime audio feel easier to drift away from when used intentionally.