THE FEELING OF WHAT HAPPENS

Body and Emotion in the Making of Consciousness

By Antonio R. Damasio

Harcourt Brace. 386 pp. $28

We've all experienced it many times. It may come when you're riding a bike and the wind blows in your hair or when a great poem causes something to burn beneath your sternum or when you're overcome by love while kissing a sleeping child. It's the rush of consciousness, the intense I can feel that I'm alive.

Consciousness may not be the greatest riddle philosophers have sought to explain over the ages, but it's certainly the most democratic and accessible one. Antonio Damasio, an eminent neuroscientist, endeavors to dissect and explain consciousness in "The Feeling of What Happens." It is a daunting and difficult task, and his is a daunting and difficult book.

Damasio, whose "Descartes' Error" gained wide attention, is exploring the edge of the precipice where the solid ground of science ends and the ethereal world of epistemology begins. He employs knowledge of neuroanatomy--and, in particular, insights gained from people with brain damage--to create what's essentially a theory of consciousness. The reader spends much of the time cantilevered over the precipice, unsure if the platform he is standing on is built of substance or abstraction.

As you can see, it's hard to talk about consciousness in concrete terms. Try doing it for an entire book!

It's easiest to begin, as Damasio does, by saying what consciousness isn't. It isn't an idea held constantly in the mind. It doesn't depend on language. There isn't a single anatomical site where it occurs (although several neural structures must be functional for it to exist). What consciousness does require--apart from a brain--is a body with a functioning milieu interieur, in the phrase of the 19th-century French physiologist Claude Bernard.

Philosophers and some scientists, Damasio believes, have looked for the key to consciousness in the wrong place. They've located it in the neighborhood of the brain's greatest accomplishments--language, memory, creativity. What it really arises out of, however, is the guts or, more precisely, a dialogue that occurs between the brain and the guts.

The roots of consciousness are buried in the body's unsung accomplishment of maintaining internal stability, or "homeostasis." The body achieves homeostasis by sensing changes in the environment and adjusting physiological variables to compensate for them. This may mean shunting blood to the skin to dissipate heat when the sun comes out from behind a cloud. It may mean producing less urine (and changing the contents of it) when you go on a hike without a water bottle.

Myriad homeostatic adjustments are made every moment, until the moment of death. They occur without thought and, within limits, can't be controlled by choice. This infrastructure of sensors, receptors and adjustors is all but invisible to us. To say that consciousness arises out of it--now that's an unusual idea.

Damasio's theory is this: An organism, through both its unconscious homeostatic machinery and the semiconscious signals of muscle tone, balance, etc., is continuously making and remaking neural "maps," or representations, of its own physical state. (He calls these maps, collectively, the "proto-self.")

The alterations brought about by worldly encounters are themselves "mapped" in the brain--in a sense, fed back to the brain--for a very practical reason. They help the organism focus attention on the object and prepare the body for interaction with it.

Damasio writes: "As the brain forms images of an object--such as a face, a melody, a toothache, the memory of an event--and as the images of the object affect the state of the organism, yet another level of brain structure creates a swift nonverbal account of the events that are taking place in the varied brain regions activated as a consequence of the object-organism interaction. The swift, second-order nonverbal account narrates a story: that of the organism caught in the act of representing its own changing state as it goes about representing something else. But the astonishing fact is that the knowable entity of the catcher has just been created in the narrative of the catching process."

That narrative account (which Damasio believes occurs in a near-infinite series of pulses as we navigate the world) is what he calls "core consciousness." It is also the core insight of the book. It's a very plausible theory, but is there evidence for it? The answer is: some.

The evidence is indirect, drawn mostly from people who've suffered such calamities as stroke, tumor or head injury. For example, people with damage to the brain's temporal lobes so severe they can't hold new information for more than 45 seconds have normal core consciousness. So memory isn't essential to consciousness. On the other hand, people with damage to the cingulate cortex, which gets all kinds of signals from the viscera and musculoskeletal system, are fully awake but without consciousness as we would ordinarily define it. So information about the body does appear to be essential to consciousness. People with destruction of the brain's visual cortex are often able to point to where an object is located even though they can't see it. This so-called blind sight exists because some of the visual signal coming from their eyes is routed into the utility trench of unconscious or semiconscious processing. So Damasio's model of sensory encounters being displayed to the brain as something more than just sensory data seems right.

There's other evidence, too, and also a lot more to the book. The author goes on to explain how core consciousness underlies "extended consciousness," which permits imagination, anticipation and conscience. He talks a little about the implications of his theory, one being that computers will never have consciousness because they'll never have the mind-body dialogue it arises from.

Damasio, who teaches at both the University of Iowa College of Medicine and the Salk Institute in California, brings an immense amount of knowledge and a wide reading of philosophy and literature to "The Feeling of What Happens." But the book he's produced is more difficult--and far longer--than it needs to be.

It's become fashionable to bewail the state of book editing--but, I have to say, Damasio was not well served by his editor. The book is poorly organized, with many arguments interrupted with statements that this or that key concept will be explained three chapters ahead. Many of the clinical examples appear in the last third of the book but would have been more useful if they'd been presented in the overly abstract beginning and middle. There's much too much neuroanatomy in the running text, while the dedicated primer on neuroanatomy is in the appendix. In a book like this, writer and editor have to face reality and put a didactic chapter or two at the beginning.

This is a tough, important subject, and Antonio Damasio has some very insightful things to say about it. But he doesn't make it easy.

David Brown, a science writer for The Washington Post.