TIME Magazine

July 17, 1995 Volume 146, No. 3

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What is consciousness? Memory? Emotion? Science unravels the best-kept secrets of the human brain


To all outward appearances, Elliot is a perfectly normal middle-aged businessman. Despite an operation a decade ago for removal of a benign brain tumor the size of a small orange, he remains intelligent and seemingly rational, with a wry sense of humor. Yet his behavior makes it clear that there is something very wrong. After years of rock-solid competence, Elliot now has trouble keeping appointments and making decisions. He has squandered much of his life savings on a series of bad investments. And, strangest of all, the very fact that his behavior is self-destructive doesn't seem to bother him--and he keeps on making the same mistakes.

Patient "X" is much more clearly ill. She has suffered a major stroke; her entire left side is paralyzed. It's obvious to everyone that she's severely impaired--everyone, that is, except her. Ask her how she feels, and she responds, "Just fine." Point out her lifeless left arm, and she seems baffled. She can be convinced, through persistent effort, that the arm doesn't work. But a few minutes later, she has forgotten all about it.

Bill Noonan hasn't suffered any obvious physical damage to his brain. Yet for more than two decades after his return from Vietnam, he has re-experienced the most terrifying event of his life several times a week as a waking dream. "It was a night ambush," he remembers. "The first seven guys to my right were machine-gunned down. My gas mask was shot right off my hip. That was my first fire fight." Bill knew his flashbacks weren't real--but they seemed so real that it made no difference. "I didn't know what was happening," he says. "The biggest fear I had was that I was crazy."

Nothing is more morbidly intriguing, more chillingly compelling than an account of a malfunctioning mind, as medical writers have learned to their great profit. The victims of mental disease or brain damage are fascinating, not simply as exhibits in a neurological sideshow but also as stark demonstrations of how fragile reality can be. Most people agree, within limits, on the objective character of the world around them. Yet while the victims of mental disorders are certainly conscious and aware, their worlds are profoundly different from those of most of us. What can it possibly feel like, we wonder, to live without emotion, to be crippled without realizing it, to re-experience an event from the distant past complete with the fears that originally surrounded it?

As neurologists, psychologists and biologists have zeroed in more and more precisely on the physical causes of mental disorders, they have found themselves addressing a much deeper mystery, a set of interrelated conundrums probably as old as humanity: What, precisely, is the mind, the elusive entity where intelligence, decision making, perception, awareness and sense of self reside? Where is it located? How does it work? Does it arise from purely physical processes--pulses of electricity zapping from brain cell to brain cell, helped along their way by myriad complex chemicals? Or is it something beyond the merely physical--something ethereal that might be close to the spiritual concept of the soul?

Great thinkers have had no shortage of ideas on the subject. Plato was convinced that the mind must be located inside the head, because the head is shaped more or less like a sphere, his idea of the highest geometrical form. Aristotle insisted that the mind was in the heart. His reasoning: warmth implies vitality; the blood is warm; the heart pumps the blood. By the Middle Ages, though, pretty much everyone agreed that the mind arose from the brain--but still had no clear idea how it arose. Finally, in the 17th century, the French philosopher Rene Descartes declared that the mind, while it might live in the brain, was a nonmaterial thing, entirely separate from the physical tissues found inside the head. Furthermore, said Descartes in one of history's most memorable sound bites, "Cogito, ergo sum" (I think, therefore I am). His point: consciousness is the only sure evidence that we actually exist.

Until just a few years ago, unraveling the relationship of mind and brain was beyond the realm of observation and experimentation. But science has finally begun to catch up with philosophy. Using sensitive electrodes inserted deep into the gray matter of test animals, researchers have watched vision as it percolates inward from the eye's retina to the inner brain. Powerful technologies such as magnetic resonance imaging (MRI) and positron-emission tomography (PET) have also provided a window on the human brain, letting scientists watch a thought taking place, see the red glow of fear erupting from the structure known as the amygdala, or note the telltale firing of neurons as a long-buried memory is reconstructed. "What's so exciting," says Patricia Churchland, a professor at the University of California at San Diego, "is that the philosophical questions raised by the Greeks are coming within the province of science."

In response to this enormous opportunity--not just to clarify the mysteries of consciousness but also to understand and treat such devastating mind malfunctions as Alzheimer's disease, depression, drug addiction, schizophrenia and traumatic brain damage--research projects have multiplied dramatically. Over the past several years, Johns Hopkins has launched the Zanvyl Kreiger Mind/Brain Institute and Harvard has created the Mind/Brain/Behavior Initiative. And at the urging of the National Institute of Mental Health and other organizations, President Bush declared the 1990s the Decade of the Brain.

In short, the brain is a hot topic, and while a complete understanding of its inner workings will be a long time coming, the surge of interest in things cerebral has already produced tantalizing results. It turns out that the phenomenon of mind, of consciousness, is much more complex, though also more amenable to scientific investigation, than anyone suspected. Descartes was right in one sense: the mind is not a physical object, and while it exists within the brain, it has no particular location. The destruction of any given part of the brain can severely alter the mind in one way or another but not destroy it.

However, Descartes was profoundly wrong, it appears, in his assertion that mind and body are wholly independent. The mind, argues University of Iowa neurologist Antonio Damasio in his book Descartes' Error, is created by the body--specifically by the brain. Utterly contrary to common sense, though, and to the evidence gathered from our own introspection, consciousness may be nothing more than an evanescent by-product of more mundane, wholly physical processes--much as a rainbow is the result of the interplay of light and raindrops. Input from the senses clearly plays a part; so do body chemicals whose ebb and flow we experience as feelings and emotions. Memory, too, is involved, along with language--the way humans translate concepts into symbolic form.

As neurologists gain deeper insights into each of these processes, they come ever closer to the central mystery of consciousness itself. Among the front-line areas of research:


We think of learning and memory as somehow separate functions; in fact, they're not. Both are processes by which we acquire and store new data in a way that makes them retrievable later on. The storage takes place, says the current theory, as a pattern of connections among neurons, the nerve cells that serve as the brain's basic building blocks. When information--the image of a new acquaintance's face, for example--enters the brain, it arrives in the form of electric impulses streaming from the retina, up the optic nerve and into the cerebral cortex, the so-called gray matter that houses the brain's higher functions.

The impulses die away within milliseconds, but their passage reinforces the particular set of connections between this particular set of neurons, giving them the ability to re-create the image. The more often the pattern is reinforced--by repeated sightings of the person, by the effort to remember him or by connection with some other mental trigger ("This woman is attractive; she's worth getting to know better," or, "This man looks unpleasant; I need to avoid him")--the more likely, says Damasio, the pattern, or image, will not go into short-term memory, lasting weeks or months, but into permanent, long-term memory. And from there, barring brain injury, disease or old age, it can be re-created by inducing the neurons to send up electric impulses in the old, by now familiar pattern.

That's the simple version. In fact, almost every memory is made of many different patterns of neuronal connections, some for sounds, some for sights, some for smells or textures--tens of thousands of neurons firing off minute electric impulses simultaneously. The combination of all these patterns, says Larry Squire, a professor of psychiatry at the University of California at San Diego, "gives you a complete perception. The persistence of the firing patterns over time gives you the transformation from perception to memory of that object." The fact that many overlapping patterns are stored together means that a single stimulus can bring on a flood of remembrance--as Marcel Proust's taste of a cookie triggered intense memories of his childhood, which in turn inspired him to write his monumental Remembrance of Things Past.

Memories of concrete facts and events, which can in principle be retrieved on demand, are coordinated through the hippocampus, a crescent-shaped collection of neurons deep in the core of the brain. Other sorts of memory are handled by other areas. The amygdala, for example, an almond-size knot of nerve cells located close to the brain stem, specializes in memories of fear; the basal ganglia, clumps of gray matter within both cerebral hemispheres, handle habits and physical skills; the cerebellum, at the base of the brain, governs conditioned learning (as when Pavlov's dogs salivated at the ringing of the dinner bell) and some reflexes.

Damage to any one of these regions has an effect on the corresponding form of memory. A much studied patient known as HM, for example, lost much of his hippocampus in the course of surgery to relieve severe epilepsy. As a result, he could remember everything that happened to him before the surgery, but he was completely unable to form new memories. He was stuck forever in the 1950s. Yet HM was able to learn new skills, such as drawing while looking in a mirror.


Physical trauma can distort memory, presumably by destroying all or part of one of these memory-processing structures. But other sorts of shock--strong emotion, for example--can do the same. Virtually everyone who was over the age of 10 when J.F.K. was shot or when Challenger exploded remembers precisely where he or she was when the news arrived. Posttraumatic stress disorder, which affects Vietnam vets like Bill Noonan, is another good example. While the intellectual memory of emotions is routed through the hippocampus, a different, gut-level sort of memory can be involuntarily revived with terrible clarity by abnormal activity in the amygdala. "It's been an eye opener to me that individuals we study who were traumatized 25 years ago still show abnormal brain function," says Dennis Charney, head of psychiatry at the VA hospital in West Haven, Connecticut. "Severe stress can change the way your brain functions biologically."

It stands to reason that humans would have a specialized region of the brain for processing emotional perceptions and memories: if our distant ancestors hadn't had an instant and violent reaction to danger, they would not have lived very long. But other parts of the brain are apparently also involved in feeling emotions. What's most surprising is the assertion by the University of Iowa's Damasio that emotion is central to the process of rational thought.

His evidence comes from nearly two dozen patients treated by Damasio, including Elliot, the businessman who started behaving irrationally after surgery to remove a brain tumor. Elliot cannot behave rationally, even though his intelligence was not affected by his tumor. The part of the brain destroyed by invading tissue was in a region of the prefrontal cortex (see diagram) essential to decision making. But what Elliot lost, psychological testing revealed, was the ability to experience emotion. While the amygdala does process fear, his doctors argue from the example of Elliot and the other patients that other parts of the brain are also critical to regulating emotion.

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."


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.

Until recently, Zeki believed that without the area known as V1, the part of the brain that first receives input from the retina, conscious visual perception would be impossible. V1 is a sort of clearinghouse, a place where incoming signals are split up and sent to the sites where they can be processed. But one patient, a 38-year-old man whose V1 for one eye was wiped out in an automobile accident, is also quite clearly aware of motion seen by the "blind" eye even when the good eye is covered. "We find," says Zeki, "that he is consciously aware of moving stimuli and of their direction. He will tell you that the bars on a TV screen are moving left or right, toward or away, and he gets it 100% correct every time." Furthermore, notes Zeki, PET scans show that the patient's perception of motion is accompanied by the appropriate activation of V5. So how does the signal travel? Zeki is convinced the answer lies in a secondary pathway, a kind of back road created to get around the damaged area.

Indeed, the brain abhors a vacuum, observes neuroscientist Dr. Vilayanur Ramachandran of the University of California at San Diego; it craves information, and when it can't come by the data honestly, it does the best it can with what it has. One of his patients, for instance, a physical-therapy professor from San Antonio, Texas, suffered a brain hemorrhage that left a huge blank spot in her otherwise normal field of vision--or, rather, it would be blank if her brain allowed it. First, she saw a drawing of a cat, presumably supplied by her visual memory. "Then," says M.J. Blaschak, "I started to see flowers." Soon cartoon characters like Mickey Mouse began to appear. "I've got to the point where I think they're pretty funny," she says.

Another well-documented example of the brain's need to fill in the blanks is the phenomenon of phantom limbs. When an arm or a leg is amputated, the victim almost invariably "feels" sensations like pain or itching, often very strongly, in the missing limb. What's happening? The brain carries within it a mental map of the body, a well-formed sense of where every part is in relation to every other. That's why it's possible for you to extend your arm and then, with your eyes closed, bring it in to touch the tip of your nose. (Drunkenness distorts your perception of the map; thus the nose-touching sobriety test often administered by cops.)

Even when a limb is gone, its place on the mental map remains, and the neurons formerly responsible for processing sensations from it occasionally fire at random--the sensory equivalent of Mickey Mouse hallucinations. The brain also attempts to make up for the deficit physically, perhaps, suggests Ramachandran, by sprouting new sets of connections. Because neurons that process information from the arm are near those that handle the face, for example, these new connections can cause a blindfolded patient to think a gentle touch on the face is really a touch on a missing fingertip. Says Ramachandran: "Reorganization can occur in a period of weeks."


The exquisite specialization of neurons for processing very precise sorts of information--moving but not still objects, the sensation of touch on a finger that isn't there anymore--is perhaps at its most highly refined when it comes to language. As a result, brain-damaged patients can exhibit an astounding range of language problems. Some have trouble using and understanding just nouns. Others have trouble with verbs. Some patients can't produce language but comprehend it perfectly; others can speak normally but can't make any sense out of what they hear.

University of Washington neurosurgeon Dr. George Ojemann has discovered, by probing the brain with electrodes, that some neurons turn on when one is silently naming an object to oneself but not during reading and vice versa. In one bilingual patient he found neurons that were activated by Finnish but not English. In another he found neurons that changed activity with English but not Spanish. And, marvels Ojemann, "the neurons that are active when you hear a word are not active when you express it."

Until recently, scientists assumed that the brain processed language in two neatly defined boxes: Broca's area (for speech production) and Wernicke's area (for speech comprehension). The picture now emerging is far more complex. The University of Iowa's Damasio, along with his wife Hanna, also a neurologist, has recently constructed a model for how the brain processes language based on some 200 unusual case histories, most prominent among them a patient code-named Boswell. Boswell has no function in large areas of his brain, owing to an infection. One consequence is that he has no memory of recent events. Nonetheless, he is able to speak and understand language perfectly well--up to a point.

Prompted with "Denver," Boswell unfailingly responds, "Colorado." Asked to name a city in Colorado, however, he goes blank. Similarly, Boswell recognizes the category "horse" but cannot supply the example "Appaloosa." He knows "U.S. President" but not Harry Truman or Richard Nixon. Somewhere in his brain, the data may still exist, but he can no longer get at them. The reason, argue the Damasios, is that he has lost essential "convergence zones," mental switching stations that provide access to the information and relate it to other relevant data.

Using an MRI scanner, Hanna Damasio has examined the living brains of hundreds of patients, and she and her husband have identified regions they think may serve as convergence zones in the brain's left hemisphere. An area in the temporal lobe pulls together information about the names of objects, animals and people, for instance, while another area in the frontal cortex appears to act as the nexus for verbs. Yet a third oversees the task of assembling nouns and verbs into sentences.


The Damasios suspect that convergence zones--thousands of them, spread through the cortex--do more than just process language. They may also coordinate every other sort of information the brain needs--perception, memory, emotion--to be fully functional. And if that's true, the convergence zones, merging disparate pieces of information into a semblance of a whole, could be responsible for that most elusive of brain phenomena: consciousness, the sense of being in the here and now.

"Consciousness," says Antonio Damasio, "is a concept of your own self, something that you reconstruct moment by moment on the basis of the image of your own body, your own autobiography and a sense of your intended future." Missing any one of the essential parts that it's built on diminishes consciousness but does not totally negate it. Damasio has no doubt that Boswell is conscious, though the quality of that consciousness is impossible for anyone else to imagine.

However, despite our every instinct to the contrary, there is one thing that consciousness is not: some entity deep inside the brain that corresponds to the "self," some kernel of awareness that runs the show, as the "man behind the curtain" manipulated the illusion of a powerful magician in The Wizard of Oz. After more than a century of looking for it, brain researchers have long since concluded that there is no conceivable place for such a self to be located in the physical brain, and that it simply doesn't exist.

But there is no shortage of competing theories about how consciousness might arise. One, offered by the Salk Institute's Francis Crick (co-discoverer of the structure of DNA) and Christof Koch, at the California Institute of Technology, is that consciousness is somehow a by-product of the simultaneous, high-frequency firing of neurons in different parts of the brain. It's the meshing of these frequencies that generates consciousness, according to Crick and Koch, just as the tones from individual instruments produce the rich, complex and seamless sound of a symphony orchestra. The concept is highly speculative, Crick acknowledges in his book The Astonishing Hypothesis (which carries the ironic subtitle The Scientific Search for the Soul). "If you think I appear to be groping my way through the jungle," he writes, "you are right."

New York University Medical School neuroscientist Dr. Rodolfo Llinas also thinks coordinated electrical signals give rise to consciousness, though his idea is subtly different from Crick and Koch's. Llinas believes that the firing of neurons is not just simultaneous but also coordinated. Using a highly sensitive device called a magnetoencephalograph, which indirectly measures the electric currents within the brain, Llinas measured the electrical response to external stimuli (he used musical tones). What he observed was a series of perfectly timed oscillations. Says Llinas: "The electrical signal says that a whole lot of cells must be jumping up and down at the same time."

These oscillations, Llinas believes, are the basic building blocks of consciousness. What the brain does, whether asleep or awake, he notes, is make images. But these are purely mental constructions, even when they're based on external information. For example, says Llinas, "light is nothing but electromagnetic radiation. Colors clearly don't exist outside our brains, nor does sound. Is there a sound if a tree drops in the forest and no one hears it? No. Sound is the relationship between external vibrations and the brain. If there is no brain, there can be no sound."

The upshot, says Llinas: "We can say that being awake or being conscious is nothing but a dreamlike state." It is a state, Llinas concedes, that corresponds tightly to external reality. But it has no objective reality; as with a rainbow, you can perceive it but never actually touch or measure it.

Llinas' and Crick and Koch's concepts, speculative though they may be, are at least firmly rooted in biology. But you don't have to be a biologist or a neuroscientist to play the consciousness game: the mystery is intriguing enough so that researchers from a wide variety of scientific disciplines have jumped in with their own ideas. Oxford mathematician Roger Penrose, for example, argues that consciousness may arise from quantum mechanics, of all things, the same process that governs the behavior of subatomic particles.

Computer scientists come at the problem from a different direction. The mind is something like a parallel-processing computer, they argue, and consciousness is simply the coordinated signal-processing of individual "agents." These agents, described as simple computer programs, sound a bit like the Damasios' convergence zones. Computer scientists and neuroscientists seem to be arriving at theories that look, in some ways, very similar.

Does this mean that science is on the verge of understanding consciousness? Not necessarily. San Diego's Churchland compares the search for answers to a canoe trip into the wilderness. Every time the canoe rounds a bend in the river, the landscape changes. She believes the journey has barely begun and that there are bound to be surprises in store. Certainly, science has finally started to shed light on a puzzle that is not just abstract and philosophical, but intimately familiar to anyone who gives it a moment's thought. But as physicist Penrose has suggested, the notion that the human mind can ever fully comprehend the human mind could well be folly. It may be that scientists will eventually have to acknowledge the existence of something beyond their ken--something that might be described as the soul.

Reported by J. Madeleine Nash/Iowa City, Alice Park/New York and James Willwerth/West Haven Copyright 1995 Time Inc. All rights reserved.

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