Spark

by John J. Ratey

The overarching principle of the fight-or-flight response is marshaling resources for immediate needs in lieu of building for the future—act now, ask questions later. The hormonal rush of epinephrine focuses the body, increasing heart rate and blood pressure and dilating the bronchial tubes of the lungs to carry more oxygen to the muscles. Epinephrine binds to muscle spindles, and this ratchets up the muscles’ resting tension so they’re ready to explode into action. Blood vessels in the skin constrict to limit bleeding in the event of a wound. Endorphins are released in the body to blunt pain. In this scenario, biological imperatives like eating and reproduction are put on the back burner. The digestive system shuts down; the muscles used to contract the bladder relax so as not to waste glucose; and saliva stops flowing. If you’ve ever faced a nerve-racking public-speaking situation, you’ve experienced this shift in the form of a racing heart and cotton mouth. Your muscles and your brain get stiff, and you lose all hope of being flexible and engaging. Or, if the processed signal from the cortex to the amygdala breaks up, you can’t think and you freeze. Technically, the full-blown stress response should be called “freeze or fight or flight.” None of this is particularly helpful when you’re up at the podium, but the body responds in essentially the same way whether you’re staring down a hungry lion or a restless audience. Two neurotransmitters put the brain on alert: norepin...