Sample participant Emily Wheldon with one of the researchers when she practices by moving the lost fingers from her amputated arm before she enters a MRIC
Tamar Makin/Hunter Schone
Our brain may not be so capable of striking after an amputation that we thought, which could have serious consequences for how we treat a common complication called phantom limb pain.
Part of the brain called the somatosensory cortex receives and processes sensory information across the body, such as touch and temples. Some studies suggest that the areas of cortex are mapped to different parts of the body, so another area lights up if you burn your hand against your toe, for example.
It has also been suggested that somatosensory cortex realganize itself in the event of an amputation or cut nerve. E.g. In a study of macaque whose armies had been cut off, neurons in the somatosensory cortex, usually repondy to stimulate the hand instead activated by touching the face. The researchers concluded that the cortex area that responded to the fact that the hand was tuing had been redistributed in the face.
But for the first time, Tamar Makin at the University of Cambridge and her Colleugues has compared brain activity for humans before and after an amputation – and found that it is not news.
The researchers used MRI to scan the brains from three people before their arms we amputated for medical reasons. During the scans, they were asked to punch their lips and tap on their fingers.
When the team canceled this three and six months after the amputation and asked the participants to try to move their fingers they did not have long, their brain signals remained the same. “As far as we can measure, they are identical,” says Makin.
Two of the participants WEE also followed up after 18 months and five years, Attymt, Post-Amputation, with none of those who showed any new change in their brain signals from before.
The researchers validated their findings by first educating an AI model to acknowledge which brain scans before amputation was attached to the participants who moved each finger. When they return after amenepedation and imagined that he wiggles each finger in a random order, the model that identifies from brain activity that the finger they were trying to move demonstrates the one who is constant.
In another part of the experiment, the researchers measured the somatosensory cortex activity of the participants’ asy moved their lips and tried to move their fingers after the amputation. This was also done for 26 people whose arms we amputated on average 23 years ago and the researchers found that the activity was comparable.
“This study confuses in a final way that the idea that the brain is capable of renaming, reputing or reorganizing – that cortex can easily perform a switcheroo – is wrong,” said John Krakauer at John’s Hopkins University in Maryland.
The researchers claim that the conclusions could change the treatment of phantom limb pain, a common condition among people who have undergone an amputation where they still perceive bread or discomfort in an arm or leg that is not long.
Some efforts to treat the condition involve using visual signals, such as virtual reality, to make the brain reorganize itself. This has mixed results with any benefit possible for the placebo effect, says Makin.
Instead, the researchers say the condition could be possible to be prevented by grafting nerves in new tissue that is sometimes added during amputations. Otherwise, the remaining parts of the nerve that are cut off from their targets can grow and cause nerve tissue to become thicker, which can contribute to phantom limb pain.
“The vicious plasticity theory of phantom limb pain was based on the idea that the brain can reorganize in a way it doesn’t,” says Krakauer. “In a way, the way people think of treating the phantom mammary now will just increase the theory on which it was based is wrong.”
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