Sleep

During sleep, the brain not only stores memories — it erases them. Research from 2022–2023 found Arc and Homer1a can weaken less-active synapse connections. Forgetting is a feature, not a bug: clearing space helps encode new memories.

Each night, a Hummingbird enters torpor: its heart slows from up to 1,200 bpm to under 50, body temperature drops from 40°C to ~10°C, and metabolism falls 95%. Without this near-death energy saving it could starve before dawn; wing-muscle tremors wake it before sunrise.

The International Space Station orbits Earth every 92 minutes, so its crew sees 16 sunrises and sunsets daily. A 45-minute day-night cycle would wreck their sleep — so astronauts keep window shades closed and run the station on Greenwich time, regardless of the light outside.

During Sleep, the Brain switches into cleanup mode. A 2013 study found that brain cells shrink during sleep, widening the space between them by about 60%, so Cerebrospinal fluid can wash away toxic proteins such as Alzheimer's-linked beta-amyloid 10–20 times faster than when awake.