(5 of 9)
In fact, says Damasio, emotion is a key element of learning and decision making. If an investment goes sour, you feel bad about it and act more carefully next time-something Elliot could no longer do after his injury. Observes Damasio: "We can't decide whom we're going to marry, what savings strategy to adopt, where to live, on the basis of reason alone."
WINDOWS ON THE WORLD A baby born with cataracts -- an unusual but not unheard-of condition -- and left untreated for as little as six months becomes permanently and irrevocably blind. If a 60-year-old develops cataracts, an operation can restore full sight. The distinctions most of us make unconsciously and at a glance -- foreground vs. background, moving vs. stationary, vertical vs. horizontal and dozens more -- are concepts that the brain must learn. It literally has to wire itself, with neurons growing out to touch and communicate with one another in an ever more sophisticated network of connections. And if those connections are not repeatedly stimulated in the first few months of life, when the brain is still in its formative period, they atrophy and die. The rule for vision -- and most likely for the other senses as well -- is "use it right away or lose it."
Those who can use it are rewarded with a visual system of astonishing complexity, with each neuron connected to as many as 15,000 others -- trillions of connections in all. Semir Zeki, a neurobiologist at University College, London, has found that there are separate subsystems for color, shape, motion and depth. Even small injuries to one of these systems can produce severe disturbances. One of his patients, for instance, could make a fine drawing of St. Paul's Cathedral but did not know what the image depicted. Another was able to copy the shapes of a Mondrian painting but not its colors. Still another lost his ability to perceive shapes, while other patients, says Zeki, "are able to see forms when they are static but not when they are in motion."
For years Zeki used electrodes planted in monkeys' brains to tease out the secrets of visual processing; more recently he has been using high-tech positron-emission tomography to watch, noninvasively, vision taking place in humans. A PET scan detects energy-burning activity in cells by tracking the rush of blood to active areas. When a part of the brain is being used intensively, it lights up on the scanner's screen. Guided by the telltale glow, Zeki has found that a colorful painting triggers a response in a region called V4. Moving black-and-white shapes activate another region, V5.