Definition
Stress physiology is the study of how the body responds to a threat or challenge — the cascade of hormonal and nervous-system changes that prepare an organism to cope. It mobilizes energy, sharpens attention, and readies the body for action, and in the short term it is adaptive and even life-saving.
Behave gives stress its own topic because the system designed for brief emergencies behaves very differently when switched on for weeks or years. Chronic stress, Sapolsky argues, reshapes the brain in ways that ripple directly into behavior.
Why it matters
How it works
A perceived threat triggers two systems. The sympathetic nervous system acts within seconds — the familiar surge of adrenaline. Slower, over minutes to hours, the hypothalamic-pituitary-adrenal axis releases glucocorticoids such as cortisol. Together they redirect energy to muscles, raise alertness, and suspend long-term projects like digestion and repair.
The problem is duration. When stress is chronic, prolonged glucocorticoid exposure enlarges and sensitizes the amygdala while it shrinks dendrites in the frontal cortex and damages the hippocampus. The result is a brain tilted toward threat perception, weaker impulse control, and poorer emotional regulation. This is how Behave connects a stressful environment — poverty, danger, instability — to measurable shifts in how people behave.