The Center for Brain and Cognition, UCSD
In one experiment, Ramachandran used a mirror and a cardboard box to perform the first "successful amputation of a phantom limb."
The Center for Brain and Cognition, UCSD
Ever wonder how your brain communicates with your fingers and toes? It all happens deep inside the brain, in a region known as the cortex. And to explain it all, neuroscientists came up with the idea of the “homunculus,” or “little man.”
We've all heard the expression "I know it like the back of my hand." But just how well do we really understand our relationship to our hands, our legs, or any of our other various body parts?
Dr. V.S. Ramachandran's innovative studies plumb many of the uncharted depths in our understanding of how our bodies and our brains relate to each other, often revealing unexpectedly complex processes for recognizing our physical selves.
In one breakthrough example, Ramachandran, a researcher at the University of California, San Diego, devised a seemingly simple experiment to explore a puzzle that has confounded doctors since at least the 16th century: the sensation that a ghostly limb remains after the amputation of a body part.
A Haunting Sensation
The French military surgeon Ambroise Pare, working in the mid-1500s, is believed to have been the first to describe this sensation.
In 1872, the experience was given its modern name when Silas Weir Mitchell, another military surgeon, coined the term "phantom limb." He based it on his experiences at Philadelphia's "Stump Hospital" during the Civil War.
According to Ramachandran, the majority of those who lose a limb experience some impression that the limb is still present. In some cases, a person may only feel it immediately after the loss. And for others, the phantom limb feels not only present, but also quite painful.
A Cause For Reflection
One of Ramachandran's patients complained that he was suffering from an excruciating cramping in his phantom arm. He felt that his phantom hand was clenched so tightly, he could feel his fingernails digging into his phantom palm. The patient was in no way delusional. He knew his arm had been amputated and that the pain was emanating from a nonexistent limb. Yet his grasp of this reality was no match for his perceived pain.
Ramachandran came up with an unusual treatment. He placed a mirror in a cardboard box and instructed the patient to place his existing hand inside the box, next to the mirror. When the patient looked down at the mirror, the reflection of his existing hand stood in as a visual replacement of his phantom limb. The patient was told to imagine that the reflection was in fact the lost limb, and to practice clenching and unclenching his hand while looking in the mirror.
To the patient's surprise — and Ramachandran's — the illusion worked. After two weeks, the patient's pain vanished, along with his perception of a phantom arm.
Mind Over Matter?
How can a limb that no longer exists "feel" pain? And why do some phantom-limb sufferers gain relief from a low-tech optical illusion that tricks their brains into believing something they already know?
Clearly, the body and the brain are intricately involved in the perception of the physical self. But when sensory experiences don't match the brain's perceptions, how is this difference reconciled, and what can we learn from the disconnect?
Herman Melville's iconic Captain Ahab, who himself was haunted by the ghost of a lost leg, ominously raised a timeless question about the discord that can occur between the body and brain: "If I still feel the smart of my crushed leg, though it be now so long dissolved; then, why mayst not thou, carpenter, feel the fiery pans of hell for ever, and without a body?" If the sensation of a leg can persist long after it ceases to exist, what about the rest of a body? Where is the line drawn between the physical self and the perception of self?
Our Bodies, Our Brains, Ourselves?
In a sense, Ramachandran explains, the entire body can be thought of as a type of phantom. And through this phantom construction, the brain can interpret our sensory experiences as we interact with our environment.
The sensation of phantom limbs, and the experiences of patients who are able to relearn the way their brains perceive these phantoms, raise a host of fascinating questions.
Neither purely physical explanations (that the irritation of severed nerves causes phantom feelings) nor purely psychological explanations (that feeling a phantom limb is a form of mental denial) can fully explain what patients describe.
Instead, Ramachandran believes that a complex interaction between the physical and the mental is at play. The brain must reconcile the physical experiences of the body with the mental image, or cortical map, it has of the body. And as the body changes, this mental image can also be remapped.
Unfortunately, in the case of phantom limbs, the mental image doesn't follow the change in the body. That's how you end up feeling pain in an arm that isn't there. But with a mirror and a little creative thinking, Ramachandran was able to trick the brain into remapping its mental image, pulling off what he calls the first "successful amputation of a phantom limb."
RADIO LAB, a production of WNYC, explores the blurring boundaries between science, philosophy and human experience.