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People who hear voices, feel missing limbs, see things that no one else does, and deny the obvious are not “crazy.” Ninety-nine percent of the time they are telling the truth, and if it seems incomprehensible, that is usually because we are not smart enough to figure out what is going on in their brains. For the most part, they are lucid, rational, and no more insane than you or I, but each of them suffers from damage to a specific part of the brain that leads to bizarre but highly characteristic changes in behavior.
Enigmatic disorders have intrigued and perplexed physicians throughout history, but usually they are chocked up as curiosities and forgotten. I believe, however, that such patients are our guides into the inner workings of the human brain—yours and mine. Far from being curiosities, these syndromes illustrate fundamental principles of how the normal human mind and brain work, shedding light on the nature of body image, laughter, dreams, depression, and other hallmarks of human nature. By moving patients out of the clinic and into the laboratory, we can conduct experiments that help reveal the deep architecture of our brains.
A key mystery that emerges when thinking about the brain is the extent to which all its intricate circuitry is innately specified by genes or to what extent it is acquired gradually as the result of early experiences, as when an infant interacts with the world.
The sense of mystery that lies at the heart of scientific pursuits is especially characteristic of the forays we make into understanding our own minds. For me, the best research strategy might be characterized as “tinkering.” Indeed, I believe that being a medical scientist is not all that different from being a sleuth.
A key mystery that emerges when thinking about the brain is the extent to which all its intricate circuitry is innately specified by genes or to what extent it is acquired gradually as the result of early experiences, as when an infant interacts with the world. This is the well-known nature-versus-nurture debate, which has been going on for hundreds of years, yet we have barely scratched the surface in formulating an answer.
The study of phantom limbs, interestingly, can shed light on this ancient nature-versus-nurture question. Phantom limbs are arms or legs, for example, that linger indefinitely in the minds of patients long after they have been lost in an accident or removed by a surgeon. Some patients experience excruciating pain in the phantom arm, hand, or fingers—pain that is not only unrelenting, but also untreatable; no one has the foggiest idea of how it arises or how to deal with it.
This phenomenon is not rare: 99 percent of patients experience a phantom pain after an amputation. Why doesn’t the mind accept the loss and “reshape” the body’s image? Is our body image—and other aspects of our mind—so firmly laid down by genes that even the experience of an amputation cannot modify it?
Consider a patient who had lost his left arm above the elbow and was experiencing itching and painful sensations in his phantom fingers. I blindfolded him and, using an ordinary cotton swab, started stroking various parts of his body surface, asking him to tell me where he felt the sensations. He felt me touch his chest, shoulder, back, leg, and so on, but when I moved the swab around his cheek, he felt not only his cheek, but also his phantom thumb and fingers. Soon we had a complete map of the patient’s phantom hand—on his face.
What could explain this medical mystery of sorts? First, we need to look closely at the anatomy of the brain, particularly at how various body parts such as limbs are mapped onto the cerebral cortex, the great convoluted mantle of the surface of the brain. Each brain cell has its territory on the body surface—its own small patch of skin, so to speak, to which it responds. We call this the cell’s receptive field. A map of the entire body surface exists in the brain, with each half of the body mapped onto the opposite side of the brain. The brain’s map is continuous except for one peculiarity. The face area of the brain, instead of being near the neck where you would expect it, is dislocated and is beside the hand area.
My reasoning is that after this patient’s arm was amputated, no sensory signals were going to the hand area of the brain, leaving it hungry for new sensory input. So the sensory signals that normally come from the face skin only to the face area of the brain now invade the vacated territory corresponding to the missing hand and start activating the neurons in the adjacent hand area. Then, whatever is reading those signals higher up in the brain misinterprets them as coming from the missing hand, so when you touch the patient’s face he says you are touching his hand.
Follow-up brain imaging experiments on amputees corroborate this theory, showing changes in brain maps where, in this example, the left hand’s area in the brain’s right hemisphere is gone, invaded by the sensory input from the face. Such large-scale changes in the organization of the brain in adult humans flatly contradict one of the most widely accepted dogmas in neurology—the fixed nature of connections in the adult human brain.
The implications are staggering. First and foremost, they suggest that brain maps can change, sometimes with astonishing rapidity, as effects have been seen in patients just 24 hours after amputation. Thus, it is possible that the completely static brain maps in textbooks are highly misleading. It may be that far from signaling a specific location on the skin, each neuron in the map is in a state of dynamic equilibrium with other adjacent neurons; its significance depends strongly on what other neurons in the vicinity are (or are not) doing.
Another striking example of cross-wiring in the brain is a phenomenon called synesthesia, or mingling of the senses. Synesthetes are otherwise perfectly normal people whose senses are mixed up. For example, every time they hear a specific tone they experience a color, such that C-sharp might be red and F-sharp might be blue. Some of these people see colors when they see numbers. Every time they see a number five printed on a page, for example, it is tinged red, so that five is red, six is blue, seven is green, and so on. Similar to phantom limbs, this phenomenon is not rare: 1 in 200 people has it.
A simple clinical test proves synesthesia is real. Figure 1 at first appears to be a bunch of computerized fives. But scattered among them are some twos—it’s not easy to find them. Eventually, you can find the twos and see that they form a shape, in this instance, a triangle. If you show this figure to a synesthete, he or she will immediately see the triangle because the twos are colored differently and conspicuously pop up from the background.
What might be the cause of synesthesia? My theory is that the most common type of synesthesia, number-color mix-up, can be explained by the fact that the number area and color area of the brain are right next to each other, almost touching, in the brain. Maybe what is going on is some accidental cross talk, or cross-wiring, just as with phantom limbs. Indeed, brain imaging experiments on people with synesthesia have found that if you show them only black-and-white numbers, the color areas of their brains are activated.
What are the implications of this phenomenon? Synesthesia is more than just a quirk in some people’s brains. Indeed, I am convinced it holds tremendous implications for understanding many aspects of conscious human experience.
Consider the odd fact that synesthesia is seven or eight times more common among artists, poets, and novelists than among the general population. What do these people have in common? They are all creative; they are very good at metaphor, at linking seemingly unrelated concepts in their brains. Further, synesthesia runs in families. So if a person has the synesthesia gene expressed diffusely around the brain, he or she is going to have a much more cross-wired brain, creating a propensity toward metaphor, abstraction, and creativity.
We are all in some sense synesthetes. To demonstrate, Figure 2 shows two letters of an imaginary Martian alphabet; one is kiki, the other bouba.
Ninety-eight percent of people in experiments say the jagged shape is kiki and the amoeboid shape is bouba. Why is that? Because the look and the sound of kiki share one property: the kiki visual shape has a sharp inflection and the sound “kiki,” represented in your auditory cortex—in the hearing centers of the brain—also has a sudden inflection of sound. The brain performs a cross-modal synesthetic abstraction, realizing that the only thing they have in common is the property of jaggedness.
The ability to form cross-modal abstractions is something that humans excel in. I suggest that it is the basis of the evolution of language. The bouba-kiki example shows a preexisting translation between the visual appearance of an object (represented in the fusiform gyrus of the brain) and its auditory representation (in the auditory cortex). This is admittedly a very small bias, but that is all that is needed to get something started in evolution.
In addition to this cross-modal effect, there is also a preexisting, built-in cross-activation between the visual in the fusiform gyrus and the motor Broca’s area in the front of the brain that controls the activation of muscles in the lips, tongue, and mouth. For example, say “teeny weeny” or “enormous” and think about what your lips are doing. We have a preexisting bias to map certain visual shapes onto certain sounds in the Broca’s area of our brains.
Finally, the hand area and the mouth area are right next to each other in the brain. There is a spillover of signals that causes the echoing of hand movements by your lips, tongue, and mouth—a phenomenon much more prevalent in children than in adults—that I call synkinesia.
So now we have three things in place: hand to mouth; mouth in Broca’s area to visual appearance in the fusiform gyrus and auditory cortex; and auditory to visual, the bouba-kiki effect. Each of these is a small effect, but acting together there is a synergistic bootstrapping that leads to an avalanche, culminating in the emergence of language.
Scientists have begun to approach questions concerning the malleability of the adult brain and even the neurology of metaphor and creativity. The question for educators is, How can we tap the mind power that anomalies such as those described above show is within us? How do we maximize individual potential? These questions have not yet been answered. I believe, though, that by training students in poetry, metaphor, art, and humor we will help shape more creative and imaginative human beings—skills that may very well spill over into other areas of the brain.
It is a unique privilege for our generation—and our children’s—to witness what I believe will be the greatest revolution in the history of the human race: understanding ourselves as we transform our understanding of the human brain. The prospect of doing so is at once exhilarating and disquieting.
V.S. Ramachandran is director of the Center for Brain and Cognition and professor of neurosciences and psychology at the University of California, San Diego and an adjunct professor of biology at the Salk Institute. Newsweek magazine recently named him a member of “The Century Club”—one of the hundred most prominent people to watch in the next century.