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A masterful update on how the brain operates.

At the beginning, neuroscientist Eagleman notes how DNA gets all the credit for being the basis of life but deserves only half. Every animal today possesses DNA identical to that of 30,000 years ago, and its behavior is also indistinguishable. A caveman with identical DNA might look like us, but their actions and thoughts would be utterly foreign. Credit goes to the human brain, entirely the creation of DNA at birth but unfinished. “For humans at birth,” writes the author, “the brain is remarkably unfinished, and interaction with the world is nec­essary to complete it.” Unlike an arm or stomach, the brain is a dynamic system, a general-purpose computing device that changes in response to experience. With this introduction, Eagleman is off and running. In the first of many delightful educational jolts, he notes that the mature brain contains regions with specific functions, but under magnification, its billions of nerve cells, which form trillions of connections, look the same. What’s happening? The brain does not think or hear or touch anything. “All it ever sees are electrochemical signals that stream in along different data cables,” writes the author, but it works brilliantly to extract patterns from this input. As we age, our brain figures out a set of rules, which the author lays out in his conclusion. At birth it possesses enormous flexibility because it must literally learn how to function. Children can learn several languages fluently, but after age 10, new languages come with an accent. If a child is kept in the dark and silence for several years after birth, they will never see or talk. Neurons compete as fiercely as they cooperate. If one area stops functioning, others take over. Thus, when the vision region falls silent from blindness or even a few hours in a blindfold, input from hearing or touch moves in. To fend off this intrusion during sleep, Eagleman theorizes, our vision area continues to operate by generating dreams.

Outstanding popular science.