Phantom limb pain is likely to be caused by a reorganisation of the wiring in the brain, a new study has found.
And the findings by scientists in Japan and England could lead to a treatment with artificial intelligence techniques, they say.
The researchers, led by a group from Osaka University in Japan with the University of Cambridge, used a brain-machine interface to train a group of 10 people to control a robotic arm with their brains.
They found that if a patient tried to control the prosthetic by associating the movement with their missing arm, their pain increased. Conversely, if they were trained to associate the movement of the prosthetic with the unaffected hand, their pain decreased.
The results show that patients with chronic pain associated with amputation or nerve injury had ‘crossed wires’ in the part of the brain that is linked to sensation and movement.
However, they write in Nature Communications, the pain can be treated if that disruption is fixed.
Study co-author Dr Ben Seymour, a neuroscientist based in Cambridge’s Department of Engineering, wanted to see if an engineering solution could be found, rather than a drug treatment.
It has long been believed that the cause of phantom limb pain is faulty ‘wiring’ of the sensorimotor cortex.
Using this premise, Dr Takufumi Yanagisawa from Osaka University, Dr Seymour and colleagues used a brain-machine interface to decode the neural activity of the mental action needed for a patient to move their ‘phantom’ hand.
The decoded phantom hand movement was then converted into a robotic neuroprosthetic, using artificial intelligence techniques.
“We found that the better their affected side of the brain got at using the robotic arm, the worse their pain got,” said Dr Yanagisawa. “The movement part of the brain is working fine, but they are not getting sensory feedback – there’s a discrepancy there.”
When the technique was changed so that they trained the ‘wrong’ side of the brain, the patients reported significantly less pain.
Dr Seymour said that while the results are promising, the effects are temporary. To be effective long term, a large piece of medical equipment is required, however he believes that a treatment based on their technique could be available within five to ten years.
“Ideally, we’d like to see something that people could have at home, or that they could incorporate with physio treatments,” he said. “But the results demonstrate that combining AI techniques with new technologies is a promising avenue for treating pain, and an important area for future UK-Japan research collaboration.”
Takufumi Yanagisawa et al. Induced sensorimotor brain plasticity controls pain in phantom limb patients. Nature Communications 27 October 2016; doi: 10.1038/ncomms13209
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