Researchers from Japan and the UK have determined that a reshuffling in the brain is the reason for phantom limb pain. Specifically, say the researchers, “a ‘reorganisation’ of the wiring of the brain is the underlying cause of phantom limb pain…”
The group from Osaka University in Japan and the University of Cambridge used a brain-machine interface and trained 10 people to control a robotic arm with their brains. If a patient tried to control the prosthetic by associating the movement with their missing arm, say the researchers, it increased their pain, but training them to associate the movement of the prosthetic with the unaffected hand decreased their pain.
Essentially, says the October 27, 2016 news release, “there are ‘crossed wires’ in the part of the brain associated with sensation and movement, and that by mending that disruption, the pain can be treated. The findings could also be applied to those with other forms of chronic pain, including pain due to arthritis.”
“We found that the better their affected side of the brain got at using the robotic arm, the worse their pain got, ” said co-author Takufumi Yanagisawa from Osaka University. “The movement part of the brain is working fine, but they are not getting sensory feedback—there’s a discrepancy there.”
As indicated in the news release, “The researchers then altered their technique to train the ‘wrong’ side of the brain: for example, a patient who was missing their left arm was trained to move the prosthetic arm by decoding movements associated with their right arm, or vice versa. When they were trained in this counter-intuitive technique, the patients found that their pain significantly decreased. As they learned to control the arm in this way, it takes advantage of the plasticity—the ability of the brain to restructure and learn new things—of the sensorimotor cortex, showing a clear link between plasticity and pain.”
Co-author Dr. Ben Seymour, a neuroscientist based in Cambridge’s Department of Engineering, told OTW, “The laboratory in Osaka has a strong interest in developing brain-controlled prostheses for people who have paralysis of some sort—ranging from loss of limb to severe ALS [amyotrophic lateral sclerosis or Lou Gehrig’s disease]. These patients also usually have severe chronic pain, so when developing prostheses, the effect on pain is an important consideration.”
“We think it is likely that the same mechanism—cortical reorganisation—may also underlie a lot of the pain in patients with arthritis, and may explain why surgery isn’t as effective for pain as we sometimes wish. This is something we are now planning to study. If so, then these findings might lead us to new ways to understand and treat pain in conjunction with surgery in the future.
