Circadian Rhythm & Sleep Homeostasis
Nathaniel Kleitman / Satchin Panda · 1939
"Two processes govern sleep — a 24-hour circadian clock that schedules alertness, and a homeostatic pressure that builds with time awake — and violating either by irregular light, meals, or bedtime impairs cognition the next day more than most people realize."
Kleitman showed in the 1930s that body temperature, alertness, and sleep are not random — they follow a clock. Panda showed in the 2010s that when you eat and when you see light shifts that clock as strongly as when you sleep.
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Fight-or-Flight & the Amygdala Hijack
"Cannon's fight-or-flight describes the body's rapid mobilization under threat, and LeDoux showed the amygdala can route a fear signal before conscious cortex catches up — so you react before you have a reasoned perception of what you're reacting to."