Dr. V.S. Ramachandran is a neurologist and professor at the University of California, San Diego, who studies the neural mechanisms underlying human behaviors. He has written several books about unlocking the mysteries of the human brain.
In his latest, The Tell-Tale Brain, Ramachandran describes several neurological case studies that illustrate how people see, speak, conceive beauty and perceive themselves and their bodies in 3-D space.
Take, for example, the clinical phenomenon known as the "phantom limb." In the majority of cases where people have lost limbs, they continue to vividly feel the presence of the missing limb. Chronic phantom pain — which strikes roughly two-thirds of patients who have had a limb removed — can become so severe that patients seriously contemplate suicide.
Where Phantom Limb Pain Originates
Several years ago, Ramachandran proposed that phantom limb pain might be caused by changes in the brain — not, as most people thought, in the peripheral nerves near the phantom limb.
"[It] was based on an idea that there's a complete map of the body's surface on the surface of the brain," he tells Fresh Air's Dave Davies. "So every point on the body's surface has a corresponding point in the brain. Now the curious thing about this map is, even though it's continuous, the face area of the map is right next to the hand area instead of being near the neck where it should be."
Ramachandran suspected that once an arm was amputated, the area in the brain mapped to that arm was deprived of sensory inputs it was used to receiving — and became hungry for new sensations.
If that was true — and if the face area of the brain map invaded the territory corresponding to the hand area of the brain map — touching the face would activate the sensations in the hand area of the brain. Patients would then feel pain on their bodies.
Ramachandran tested his theory by blindfolding patients so that they wouldn't know where he was touching them — and then touched various parts of the body. Sure enough, when touching a patient's face on the same side as an amputated limb, the patient reported that he could feel the sensation in his phantom missing limb. What this proved, he explains, is that the brain is constantly remapping itself as we age.
"What we were all taught as medical students a decade or two ago is that connections in the fetal brain are fixed during infancy or fetal life by genes, and then as you grow into adulthood, the maps crystallize and are there permanently," he says. "But we are finding that this is not true. Even the basic sensory map in the brain gets completely reorganized in a matter of weeks. This challenges the dogma that all medical students are raised with that no new connections or pathways can emerge in the adult brain. That was news 10 or 15 years ago. Now it's widely accepted."
How To Unlearn Phantom Pain
After realizing that phantom limb pain originated in the brain — and that the brain could be remapped — Ramachandran realized he needed to trick patients' brains into unlearning the pain associated with their phantom limbs.
"We call this phenomenon learned pain or learned paralysis," he says. "The question is: Can you unlearn the pain or paralysis by allowing the brain to send a command to the phantom and have the phantom move — or appear to move — in response to the command. But how do you do that? The guy doesn't have an arm. How do you make the arm appear to move?"
The answer, Ramachandran discovered, was a simple $5 mirror box which he propped up on a table parallel to a patient's nose. The patient put his phantom limb on the nonreflecting side of the mirror and his normal arm on the reflecting side of the mirror. When the patient then looked at the reflecting side, it appeared as if the phantom limb had returned. (It was, in fact, a reflection of the patient's existing arm.)
"If the patient then starts moving his hand, clapping his hand or conducting an orchestra or waving goodbye while looking in the mirror, he's going to see the mirror reflection of the normal hand superposed on the phantom, moving in command with the command sent to the phantom arm," says Ramachandran. "So you're going to get the visual illusion that the phantom limb is obeying the command."
Though patients know intellectually that their phantom limbs have not returned, they are able to successfully trick their brains into thinking that their limbs have returned.
"It not only looks like it's there, it feels like it's there," says Ramachandran. "Patients say, 'When I move my normal hand, the phantom arm looks like it's moving. When I open the normal fist, the phantom hand — whose fist I could not open for months — suddenly feels as if it is opening as a result of the visual feedback, and the painful cramp goes away.' This is a striking example of modulation of pain signals by vision."
Dr. V.S. Ramachandran, called the "Marco Polo of neuroscience" by Richard Dawkins, is the author of several books on the brain, including Phantoms in the Brain: Probing Mysteries of the Human Mind and A Brief Tour of Human Consciousness: From Impostor Poodles to Purple Numbers. He gave the 2003 BBC Reith Lectures and has published more than 180 papers in scientific journals including Nature and Science.