Phantom Limb Pain and the sensorimotor cortex
From my days working with amputees I was aware of phantom limb pain as a frequently troubling side effect of limb amputation. The amputee feels as if the limb is still intact and many of them suffer from chronic, burning or hypersensitive type of pain which is difficult to deal with.
Researchers from Osaka University in Japan in collaboration with the University of Cambridge, have discovered that a ‘reorganisation’ of the wiring of the brain is the underlying cause.
The research used a brain-machine interface to train a group of ten individuals to control a robotic arm with their brains. They found that if a patient tried to control the prosthesis by associating the movement with their missing arm, it increased their pain, but training them to associate the movement of the prosthetic with the unaffected hand decreased their pain.
A popular but increasingly controversial theory has been that phantom limb pain results from maladaptive reorganization of the sensorimotor cortex, suggesting that experimental induction of further reorganization should affect the pain, especially if it results in functional restoration.
However, contrary to their expectation that functional restoration would reduce pain, the Brain Machine Interface training with the phantom hand intensified the pain.
In contrast, BMI training designed to dissociate the prosthetic and phantom hands actually reduced the pain. These results reveal a functional relevance between sensorimotor cortical plasticity and pain, and may provide a novel treatment with BMI neurofeedback.
“Induced sensorimotor brain plasticity controls pain in phantom limb patients” by Takufumi Yanagisawa, Ryohei Fukuma, Ben Seymour, Koichi Hosomi, Haruhiko Kishima, Takeshi Shimizu, Hiroshi Yokoi, Masayuki Hirata, Toshiki Yoshimine, Yukiyasu Kamitani and Youichi Saitoh in Nature Communications. Published online October 27 2016 doi:10.1038/ncomms13209