“Lithium regulates the proteins that control the body’s inner clock. This clock runs, oddly, on DNA, inside special neurons deep in the brain. Special proteins attach to people’s DNA each morning, and after a fixed time they degrade and fall off. Sunlight resets the proteins over and over, so they hold on much longer. In fact, the proteins fall off only after darkness falls—at which point the brain should “notice” the bare DNA and stop producing stimulants. This process goes awry in manic-depressives because the proteins, despite the lack of sunlight, remain bound fast to their DNA. Their brains don’t realize they should stop revving. Lithium helps cleave the proteins from DNA so people can wind down. Notice that sunlight still trumps lithium during the day and resets the proteins; it’s only when the sunlight goes away at night that lithium helps DNA shake free. Far from being sunshine in a pill, then, lithium acts as “anti-sunlight.” Neurologically, it undoes sunlight and thereby compresses the circadian clock back to twenty-four hours—preventing both the mania bubble from forming and the Black Tuesday crash into depression.”