This new model of memory isn’t just a theory—neuroscientists actually have a molecular explanation of how and why memories change. In fact, their definition of memory has broadened to encompass not only the cliché cinematic scenes from childhood but also the persisting mental loops of illnesses like PTSD and addiction—and even pain disorders like neuropathy. Unlike most brain research, the field of memory has actually developed simpler explanations. Whenever the brain wants to retain something, it relies on just a handful of chemicals. Even more startling, an equally small family of compounds could turn out to be a universal eraser of history, a pill that we could take whenever we wanted to forget anything.