Environments, Past and Present

Abstract

For more than a century, scientists have known that acute stress activates the fight-or-flight response. When your life is on the line, your body reacts instantly: your heart races, your breath quickens, and a cascade of hormones sets off physiological changes that collectively improve your odds of survival. More recently, scientists have come to understand that the fight-or-flight response takes a toll on the brain and the body—particularly when stress is chronic rather than acute. Systems designed to handle transient threats also react to stress that occurs again and again, for weeks, months, or years. It turns out that poverty, abuse, and other forms of adversity repeatedly activate the fight-or-flight response, leading to long-term effects on the immune system and brain, which in turn increase the risk for an array of illnesses, including asthma, diabetes, arthritis, depression, and cardiovascular disease. Pioneering neuroscientist Bruce McEwen called this burden of chronic stress “allostatic load.”