Amputees' brains remember missing limbs years later
Findings could influence next generation of prosthetics and treatment of 'phantom pain.'
A small study by a team of researchers in England has shown that amputees' brains remember missing limbs to such a degree it's as if they never lost them in the first place. The study has given new insight into the workings of the human brain and counters a previously held belief of the medical community.
Dr. Tamar Makin, a graduate of Hebrew University in Jerusalem, now leads the team of researchers at Oxford University's Hand and Brain Lab that conducted the study, "There's this very powerful notion, both in neuroscience and in medicine, that if you lose an input to one brain area it's not just going to retire and become unemployed. It's going to be taken up by other functions," she told From The Grapevine.
But the study showed that that's not necessarily the case. By analyzing the brain activity of individuals who had lost their left hand decades ago, what they found was quite the opposite. Rather, the brain had created a detailed map of the amputees' hands and fingers that persisted for years even after the loss of the limbs.
Dr. Tamar Makin's research may change the way we think about prosthetics. (Photo: Bryan Jones)
To arrive at their conclusion the team used an ultra-high power MRI scanner to look at brain activity in two people who had both lost their left hand more than 20 years ago but who still experienced vivid phantom sensations — sensations that their hand and fingers were still present — and eleven people who retained both hands and were right handed. Each person was asked to move individual fingers on their left hand.
Sanne Kikkert, a graduate student on Dr. Makin's team, detailed the results: "We found that while there was less brain activity related to the left hand in the amputees, the specific patterns making up the composition of the hand picture still matched well to the two-handed people in the control group," she said.
"We confirmed our findings by working with a third amputee, who had also experienced a loss of any communication between the remaining part of their arm and their brain. Even this person had a residual representation of their missing hand's fingers, 31 years after their amputation."
Dr. Makin told us the findings could prove beneficial in treating phantom pain — the pain suffered by amputees in places where limbs have been lost.
"80% of amputees experience phantom pain and for a smaller number it's so excruciating as to be debilitating," she said. "There's really been nothing the medical community could do about it because you can't treat what's not there."
She also said it could help in the development of neuroprosthetics — prosthetic limbs controlled directly by the brain — the evolution of which has operated under the assumption that a person would over time lose the brain area that could control the prosthetic.
Dr. Makin, who moved from Israel to England seven years ago to work at Oxford, said the study had profoundly influenced how she would approach her own research moving forward. "The way we think about any sensory cortex is that it is shaped and driven by experience. So if you play a musical instrument or do something quite dexterous with your hands then that's going to slightly change it," she told us.
"And the fact that we have people who for 20 or thirty years not only don't have a hand but haven't received any organized input from their hands — they haven't used that hand — and nothing has changed really made me rethink how experience shapes the brain," she continued, while adding, "We've only been focusing on half of the picture. Some things change but some things, they never change."
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