Mapping The Brain

If you have one of 1,000 test copies of this magazine, sometime while you read this article a specially embedded microchip will give you a mild electric shock. If you have an ordinary copy, there is no danger.

Deep inside your brain, a little knob-shaped organ no bigger than a chickpea is going like gangbusters right now (at least if you're the gullible type). The organ is called the amygdala, and when neuroscientists gave volunteers a version of this warning--that sometime during an experiment they might receive an electric shock-the nerve cells in the volunteers' amygdalae lit up like telephone lines during the World Series earthquake. How did the scientists know? They were reading their volunteers' minds-by mapping their brains.

It seems only fitting that, with 1492 in the air, one of the greatest uncharted territories in science is finally attracting its own cartographers. The terrain is the gelatinous three-pound world called the Brain, and the map makers' sextants are devices that stare right through the solid wall of the skull. The maps they are slowly piecing together will carry labels even more provocative than the 15th century's "Disappointment Islands." They will show, with the precision of the best atlas, the islands of emotion and the seas of semantics, the land of forethought and the peninsula of musical appreciation. They will show, in short, exactly where in the brain cognition, feelings, language and everything else that makes us human comes from.

It's called a functional map of the brain, and it is one of the grandest goals of what Congress and President George Bush have declared the "Decade of the Brain." The neuroscientists might actually achieve it, thanks to the technologies that open windows on the mind. With 100 billion cells-neurons-each sprouting about 1,000 sylphlike fingers to reach out and touch another, it's quite a view. "The brain is the last and greatest biological frontier," says James Watson, codiscoverer of the double helix that is DNA. In a book from the National Academy of Sciences released last month entitled " Discovering the Brain," Watson calls it "the most complex thing we have yet discovered in our universe."

To make sense of the jungle of neurons and swamps of gray matter, it won't be enough to take snapshots with, say, a CAT scanner. Computer-assisted tomography produces lovely pictures of brain structure, but can't distinguish between a live brain and a dead one. The challenge for brain cartography is to beyond structure-all the cranial continents have been identified-to create a detailed diagram of which parts do what. For that, the map makers rely on an alphabet soup of technologies, from PETs to SQUIDs (page 68), that pinpoint neural activity in all its electrical, magnetic and chemical glory.

Each technique adds a different piece to the neural puzzle. Some magnetic imaging, for instance, is so spatially precise it can distinguish structures as small as a millimeter, but is much too slow to reveal the sequence in which different clumps of neurons blink on during a thought. But together, the technologies are yielding a map as detailed as that expected to be drawn for human DNA--though much more interesting. For instance, neuroscientists thought that the cerebellum was the patron saint of the clumsy, the region that controls balance and coordination and so keeps people from stumbling. New studies suggest that the cerebellum may also house the memory of rote movements: touch-typing or violin fingering may originate in the same place as the command not to trip over your own two feet. "Perhaps the brain can package a task very efficiently, even take it out of the conscious world [of the cortex] and just run the program unconsciously," speculates neurologist John Mazziotta of the University of California, Los Angeles. The mapping expeditions have also perked up philosophy. Once again, eminent thinkers are dueling over whether the mind is anything more than the brain (following story).

The lofty abilities of the brain reside in the cortex, the quarter-inch-thick cap of grooved tissue that runs from the eyebrows to the ears. The cortex consists of two hemispheres, a left and a right, each composed of four distinct lobes (diagram, page 67) and connected by a highway of fibers called the corpus callosum. Studies of patients with brain lesions, as well as electrical stimulation of conscious patients during brain surgery, have pinpointed scores of regions that seem to specialize in particular jobs. Some make sense of what the eyes see. Others distinguish irregular from regular verbs. But research on brain-damaged people always runs the risk that they aren't representative. The power of the new imaging techniques is that they peer inside the minds of the healthy. " They allow us to study how the living brain performs sophisticated mental functions," says neuroscientist Eric Kandel of Columbia University. "With them, we can address the most complicated questions in all science."

Some of the maps confirm what studies of brain-damaged patients had already shown. Last November, for instance, researchers reported on a PET (positron emission tomography) study confirming that the hippocampus, a little sea-horse-shaped structure deep inside the brain, is necessary for forming and retrieving memories of facts and events (NEWSWEEK, Nov. 25,1991). That's just what studies of amnesiacs had found. But while confirmation of old notions is nice, what the brain mappers really want is to stumble upon a Northwest Passage, connections that were totally unexpected, symphonies of neurons that had gone completely unheard. PET may do that. For a PET scan, volunteers are injected with radioactive glucose. Glucose, the body's fuel, mixes with the blood and wends its way to the brain. The more active a part of the brain is, the more glucose it uses. PET sensors array around the head of a volunteer, who sits in a modified dentist chair with his head behind black felt to keep out distractions pinpoint the source of the radioactivity, and hence the heightened activity. They send the data to computers that produce two-dimensional drawings showing the neural hot spots.

PET is hardly the only technique to discover that the brain is organized in weird ways. Take music-as a team at New York University did. It has pioneered the use of the SQUID (superconducting quantum interference device), which senses tiny changes in magnetic fields. (When neurons fire, they create an electric current; electric fields induce magnetic fields, so magnetic changes indicate neural activity.) The device looks like a hair dryer from hell. When the NYU scientists aimed a SQUID at a brain listening to various notes, they found an eerie reflection of the black and white keys on a piano. NYU physicist Samuel Williamson and psychologist Lloyd Kaufman saw not only that the brain hears loud sounds in a totally different place from quieter sounds, but also that the areas that hear tones are laid out like a keyboard. "The distance between brain areas that hear low C and middle C is the same as the distance between areas that hear middle C and high C--just like on a piano," says Williamson.

In another unexpected find, brain systems that learn and remember faces turn out to reside in a completely different neighborhood from those that learn and recall man-made objects. The memory of a face activates a region in the right part of the brain that specializes in spatial configurations. The memory of a kitchen spatula, in contrast, activates areas that govern movement and touch. "What counts is how the brain acquires the knowledge," says neuroscientist Antonio Damasio of the University of Iowa College of Medicine. "The brain lays down knowledge in the very same systems that are engaged with the interactions"in the case of a spatula, the memory resides in that part of the cortex that originally processed how the spatula felt and how the hands moved it.

Imagine four squares and form them into an "L." "Now imagine two squares side by side. Fit the pieces into a smooth rectangle.

An area near the left side of the back of your head snapped to attention, especially if you're doing this without pencil and paper. It's one of the brain's centers for spatial reasoning-no surprise there. The astonishing thing is how hard it works. At the Brain Imaging Center at UC, Irvine, Richard Haier had volunteers play the computer game Tetris while in a PET scanner. In Tetris, players move and rotate squares, in various configurations such as an "I" or an "L," to create a solid block. This year, Haier found that people used lots of mental energy while learning Tetris, but after practicing for several weeks their brains burned much less energy--even though their scores had improved 700 percent. " Watching someone play Tetris at an advanced level, you might think, 'That person's brain must really be active'," says Haier. However, "[their] brains were actually not working as hard as when they played for the first time." Even more intriguing, the greater a volunteer's drop in the energy his brain used, the higher his IQ.

Intelligence, then, may be a matter of efficiency-neural efficiency. Smart brains may get away with less work because they use fewer neurons or circuits, or both. Conversely, when a less smart brain thinks, lots of extraneous or inefficient neural circuits crackle. Intelligence, in this model, is a function not of effort but of efficiency. Intelligence "may involve learning what brain areas not to use," says Haier.

One key to intelligence may be "pruning." At birth, a baby's brain is a rat's nest of jumbled neurons. It uses up more and more glucose until the child is about 5, when it is rough twice as active as an adult's. Then glucose use and the number of circuits plummet until the early teen years. This is called neural pruning, and Haier speculates it's the key to neural efficiency. More intelligent people may get that way by more pruning, which leaves remaining circuits much more efficient. Might pruning explain the link between genius and madness? "Overpruning may result in the high intelligence often associated with creativity, but hyperpruning may result in psychopathology," suggests Haier. No one has a clue as to why some brains prune their circuits like prize bonsai and others let them proliferate like out-of-control wisteria. Edward Scissorhands, call Dr. Frankenstein.

Decide whether any words in this sentence rhyme. Now name an animal with a very long neck.

Your vision center, at the back of your head right behind your eyes, has been buzzing with activity as you read. That's to be expected. But until recently, scientists thought that all language skills-reading, writing and rhyming--were contained within a single brain circuit. They were wrong. Naming and reading are governed from two different places. You can thank several clusters of neurons scattered across the cortex for coming up with " giraffe"; that's where naming comes from. But these clusters are not necessarily involved in reading. Similarly, regions that process spoken language, midway back on the left side of your head, told you that no words in the sentence rhymed. That spot had been basically dormant until then: contrary to psych texts, words do not have to be pronounced in the mind's ear in order for the brain to assign them a meaning. In the new model, the brain processes words by sight or sound. The result goes to the left frontal lobe, which imparts meaning to information received by either sense.

That finding undercuts psychologists' certainty that language is processed like a football play. Scholars had thought that to speak aloud a written word, the printed word had to pass from the visual cortex that saw it to the area that decoded it. From there, it was lateraled to the area in the frontal lobe that pronounces it. Touchdown! " The surprise is that when you see a word, and say it, it doesn't pass through the auditory part of the brain at all," says neuroscientist and PET pioneer Marcus Raichle of Washington University in St. Louis. " The old idea was that before you could say a word, the brain must change a visual code into a sound code. We don't see that at all." In fact, auditory areas of the brain are not active when one speaks, says Raichle: " You don't listen to what you say in the same way that you hear what others say."

Board. Tweal. Nlpfz.

Your visual cortex is still on the job, seeing words. But so are areas way outside the vision centers. To get at the great questions of language, Raichle and colleagues started small-with single words. As words flashed by on a computer screen, one per second, the PET volunteers' visual cortex lit up, as expected. But so did dime-size clusters of neurons way outside the vision centers, on the left side of the brain. Perhaps they hold the meanings of words. Call it Semantic Central. These same areas lit up when the volunteers saw nonwords that nevertheless obeyed rules of English"tweal"-as if the brain were scrambling to assign a meaning to something that by all rights should have one. These semantic areas stayed dark when the volunteers saw consonant letter strings-nlpfz. Since babies aren't born knowing which letters form words and which don't, the brain has apparently learned what conforms to rules of English spelling and what does not. And it has carved out special zones that do nothing but analyze these rule-obeying strings of letters.

Supply a verb for each noun: pencil, oven, broom. And tell which animals in this list are dangerous: tapir, lion, lamb.

Two clusters in your cerebral cortex lit up. One, in the left frontal lobe, kicks in when the brain deals with meanings. But it gets bored easily. If you were asked to supply verbs for the same nouns, or analyze the same animals, over and over, the region wouldn't lift a neuron: it seems to play a role only "in the acquisition of a new skill, in this case linguistic," says Raichle. Then it bows out. The brain can still provide "write" for "pencil," but seems to do so on automatic pilot. In addition, to focus on the word problems, the "anterior cingulate gyrus" turns on, as it does whenever "subjects are told to pay attention," says Raichle. It also shines with activity when researchers ask volunteers to read words for colors-red, orange, yellow--written in the "wrong" color ink, such as "red" written in blue. Some neural arbiter must choose which processing center, that for reading "red" or naming blue, to activate. As the brain tries to resolve the conflict, the front of something called the cingulate cortex, located an inch or so beneath the center line of the front of the scalp, positively glows.

Scans make it clear that the brain is a society of specialists. Different grape-size regions process proper but not common nouns, for instance. Not only that, separate zones also harbor tiny fragments of a larger idea, says Antonio Damasio. It can be an idea as lofty as Truth or as mundane as silver candlesticks. The Ph.D.s haven't figured out Truth yet, but they think they have a pretty good idea how your mind's eye sees the candlestick. PET scans show that these fragments come together in time but not in space, thanks to an as-yet-undiscovered maestro that takes the disparate tones and melds them into perfect harmony. Fragments of knowledge are scattered around the brain, especially in the back of the cortex. Areas closer to the front contain what Damasio calls "combinatorial codes," which assemble information from the rear. Damasio has christened these "convergence zones"; their location varies from one person to the next. A convergence zone recalls where in the back office the different attributes of the candlestick are stored. When it's time to reconstruct the silver candlestick, the convergence zone activates all the relevant storage sites simultaneously. One bundle of nerves sends in a pulse that means "silver," another shoots out "cylinder shaped," another offers "burns." "Our sensory experiences happen in different places," says Damasio. "There must be an area where the facts converge."

PETs have seen clues to convergence zones in people who, because of brain lesions, cannot name famous faces. They register a flicker of recognition, but deny they know whose face it is. The knowledge exists, says Damasio, but is "unavailable to consciousness. " The lesion has apparently disrupted the links between the memories for various parts of a face-the shapes of its features, the tone of its skin-tucked away in the right part of the cortex and the memory of the name in another back office. The fragments remain, but the convergence zone cannot bring them together.

Sing "Row, Row, Row Your Boat." Lift your finger when you come to a four-letter word.

If you're female, tiny spots on both sides of your brain light up. If you're male, only one side does. That's the kind of map Cecile Naylor of the Bowman Gray School of Medicine saw when she scanned brains of people who had been marked with a radioactive tracer that homes in on active areas. In one task, they listened to words and raised a finger when they heard one four letters long. Women's mental acrobatics were all over the brain; men's were compartmentalized. In women but not in men, some areas associated with vision lit up. " You wonder if females are using more of a visual strategy than males," says Naylor. Perhaps they see the spelled word in their mind's eye and then count letters.

New windows into the brain are ready to open. Robert Turner of the National Institutes of Health recalls "the awe-inspiring experience" of lying inside a colossal MRI (magnetic resonance imaging) magnet as images flashed on and off before his eyes. The machine recorded changes in his brain that came 50 milliseconds a art. " You can see different areas light up at different times," marvels Turner. NYU uses five SQUIDs to spy on the brain; the Japanese are hard at work on a 200-SQUID array. At Massachusetts General Hospital, researchers are putting the finishing touches on "ecoplanar MRI," which snaps a picture of the brain in just 45 milliseconds. The brain's cartographers are poised to glimpse thoughts, feelings and memories as they spring from one tiny clump of cells, ignite others and blossom into an idea or a passion, a creative leap or a unique insight. When they do, science may truly have read the mind.

Illustration: ( LEWIS E. CALVER)

Plan for the future, control movement and produce speech.

Hear and interpret music and language.

Receive and process data from the senses.

Specialize in vision.

Covers the four lobes that make up the left and right hemispheres of the brain. It is just a few diameters thick.

Generates emotions from perceptions and thoughts,.

Consolidates recently acquired information, somehow turning short-term memory into long term.

Takes sensory information and relays it to the cortex.

Controls automatic body functions like breathing. It is the junction between the brain and the spine.

Governs muscle coordination and the learning of rote movements.


Each scanning device has strengths and weaknesses. PET accurately tracks brain function, but can't resolve structures less than .5 inch apart. MRI can't detect function, but can distinguish structures even .05 inch apart.