This Is Your Mind on Plants

by Michael Pollan

it’s necessary to understand something about the pharmacology of caffeine. Caffeine is a tiny molecule that happens to fit snugly into an important receptor in the central nervous system, allowing it to occupy it and therefore block the neuromodulator that would normally bind to that receptor and activate it. That neuromodulator is called adenosine; caffeine, its antagonist, keeps adenosine from doing its job by getting in its way. Adenosine is a psychoactive compound that has a depressive and hypnotic (that is, sleep-inducing) effect on the brain when it binds to its receptor. It diminishes the rate at which our neurons fire. Over the course of the day, adenosine levels gradually rise in the bloodstream, and as long as no other molecule is blocking its action, it begins to slow mental operations in preparation for sleep. As adenosine builds up in your brain, you begin to feel less alert and a mounting desire to go to bed—what scientists call sleep pressure. But when caffeine beats adenosine to those receptor sites, the brain no longer receives the signal to begin turning out the mental lights. Even so, the adenosine is still circulating in your brain—in fact, its levels continue to rise—but because the receptors have been hijacked, you don’t feel its effects. Instead, you feel wide-awake and alert. Are you really? Yes and no. How you feel is how you feel, it’s true, but as Matthew Walker, a UC Berkeley neuroscientist and sleep researcher, explains, since adenosine continu...