Healthcare (Commonwealth Union) – New research led by the University College London (UCL) scientists has revealed that the brain’s internal “map” of the body remains fixed even after a limb is amputated, challenging the long-standing belief that it reorganises itself to adjust for the loss.
Published in Nature Neuroscience, the study suggests new possibilities for treating “phantom limb” pain and indicates that operating robotic prosthetics through neural interfaces may be easier than once assumed.
Earlier work has shown that within the brain’s somatosensory cortex lies a detailed representation of the body, where distinct regions are linked to specific body parts. These maps manage sensory input such as touch, temperature, pain, and spatial awareness. For instance, touching a hot surface triggers activity in one area, while stubbing a toe sparks activity in another.
For a long time, neuroscientists widely believed that after an amputation, surrounding regions of the cortex would shift and take over the space previously dedicated to the missing limb. This assumption was based largely on post-amputation studies that did not compare brain activity before and after the loss.
Yet this has raised a puzzle. Many people who lose a limb continue to experience phantom sensations — the sense that the missing part is still there — often accompanied by feelings such as itching or pain in the absent limb. Brain imaging studies have also shown that when amputees are asked to “move” their missing fingers, their brain activity looks strikingly similar to that of people with intact limbs.
To explore this apparent contradiction, researchers at UCL tracked three patients scheduled to have one of their hands amputated. It was the first study to examine how both hand and face representations in the brain change before and after amputation. The project was directed by Professor Tamar Makin, now at the University of Cambridge, and Dr. Hunter Schone, currently at the University of Pittsburgh, with most of the work carried out while both were still at UCL.
Before surgery, all three participants could move every finger of the hand that was later removed. Inside a functional magnetic resonance imaging (fMRI) scanner — which detects patterns of brain activity — they were asked to move each finger separately as well as to purse their lips. From these scans, the researchers-built brain maps showing the representation of the hands and lips, which are positioned close to each other in the brain’s sensory layout.
The same procedure was repeated three and six months after amputation, though this time the participants were instructed to purse their lips and to imagine moving their individual fingers. One subject returned for another scan 18 months later, and another was re-examined five years after the surgery.
When the researchers compared the pre-surgery finger maps with those recorded afterward, the results were striking: the brain patterns remained remarkably stable. Even in the absence of the hand, the corresponding brain area continued to activate almost exactly as it had before.
Professor Tamar Makin, who is based at the University of Cambridge and honorary professor at the UCL Institute of Cognitive Neuroscience, as well as the senior author of the study says “Because of our previous work, we suspected that the brain maps would be largely unchanged, but the extent to which the map of the missing limb remained intact was jaw-dropping.
“Bearing in mind that the somatosensory cortex is responsible for interpreting what’s going on within the body, it seems astonishing that it doesn’t seem to know that the hand is no longer there.”
Dr. Chris Baker, co-author and researcher at the Laboratory of Brain & Cognition, National Institutes of Mental Health, indicated that if the brain reorganised itself after amputation, these technologies would not function. He further indicated that if the region that once controlled our hand were now controlling the face, these implants simply wouldn’t work and their results open a genuine pathway to advance these technologies today.
