Each human brain contains a detailed map linking specific areas to body parts like hands, lips, and feet. But what happens to this map when a body part is lost?
For years, scientists believed that after an amputation, the brain’s map undergoes major reorganization, with nearby regions taking over the space that once represented the missing limb.
This concept of large-scale neural reshaping became a key example of what neuroscientists refer to as adult brain plasticity—the brain’s ability to adapt its structure and function in response to injury, learning, or experience.
New Study Reveals Brain’s Body Map Remains Stable Long After Amputation
Our recent study, published in Nature Neuroscience, reveals a surprising finding: instead of dramatically changing, the brain’s body map stays remarkably stable—even years after an amputation.
To explore how the brain responds to losing a body part, we took a novel approach.
Working with NHS surgeons, we tracked three adults facing arm amputations due to cancer or circulation problems. We used fMRI to scan their brains before surgery and periodically afterward, some for up to five years.
While undergoing MRI scans, patients were asked to move various body parts—such as tapping individual fingers, curling their toes, or pursing their lips. This enabled us to track brain activity and create a detailed map of the body within the brain.
Tracking Phantom Limb Movements to Compare Brain Maps Before and After Amputation
Following the amputations, we conducted additional scans, this time instructing the participants to move their missing (phantom) fingers. These phantom movements aren’t imaginary—many amputees continue to experience vivid sensations from limbs that are no longer present. This allowed us to directly compare each person’s brain hand map before and after amputation.
In all three patients, the brain’s hand map remained intact and wasn’t overtaken by nearby areas like the face. This stability in the brain’s structure may explain why many amputees continue to feel their missing limbs so vividly.
However, for most amputees, these phantom sensations aren’t just neutral—they’re often painful, described as burning, stabbing, or itching. For years, the leading theory behind this pain was that the brain’s body map had been reorganized. This idea led to treatments such as mirror box therapy, virtual reality exercises, and sensory training, all designed to “repair” what was believed to be a disrupted brain map.
Our results indicate that the brain’s body map remains intact, not damaged. This may clarify why therapies aimed at “correcting” the map often perform no better than placebos in clinical trials. If there’s nothing wrong with the map, then attempting to fix it is unlikely to be effective.
The True Cause
Instead, our findings suggest focusing on other areas—such as the nerves severed during surgery. These cut nerves can develop tangled clusters that send incorrect signals to the brain. New surgical methods for amputation are being designed to preserve nerve signaling and maintain stable connections with the brain.
These discoveries carry significant implications for the advancement of prosthetic limbs and brain-computer interfaces. Advanced invasive brain-computer interfaces can directly access the preserved brain map of the amputated limb to interpret intended movements or even provide electrical stimulation to help amputees experience sensations from their missing limb.
These technologies are still being developed but have the potential to one day restore natural, intuitive control and sensation of prosthetic limbs by utilizing the preserved body map in the brain.
Our findings demonstrate that the brain maintains a robust and enduring model of the body, preserving its representations even after sensory input is lost. For amputees, this means that their missing limb continues to exist within the brain—sometimes causing discomfort, but also serving as a valuable foundation for future technological innovations.
Read the original article on: Sciencealert
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