Your brain is currently expending about a fifth of your body’s energy , and almost none of that is being used for what you’re doing right now. Reading these words, feeling the weight of your body in a chair—all of this together barely changes the rate at which your brain consumes energy, perhaps by as little as 1 percent. The other 99 percent is used on the activity the brain generates on its own : neurons (nerve cells) firing and signaling to each other regardless of whether you’re thinking hard, watching television, dreaming, or simply closing your eyes. Even in the brain areas dedicated to vision, the visuals coming in through your eyes shape the activity of your neurons less than this internal ongoing action. In a paper recently published in Psychological Review , we argue that our imagination sculpts the images we see in our mind’s eye by carving into this background brain activity. In fact, imagination may have more to do with the brain activity it silences than with the activity it creates.…