Phantom pain in amputees is a tough problem to solve.
According to The Amputee Coalition of America, there are around 2 million amputees living in America.
As diabetes rises in prevalence, amputations are increasing in line. The number of amputations caused by diabetes rose 24 percent from 1988-2009.
Beyond the obvious distress and myriad of psychological and practical problems, these procedures also carry a painful and mysterious side effect.
The sensation of pain coming from the place where an amputated limb used to reside is a common and disruptive problem in amputees.
This phantom pain is estimated to affect 80 percent of the worldwide amputee population.
The co-author of a recent study examining this phenomenon explains this sensation:
“Even though the hand is gone, people with phantom limb pain still feel like there’s a hand there – it basically feels painful, like a burning or hypersensitive type of pain, and conventional painkillers are ineffective in treating it.”
Dr. Ben Seymour
Dr. Seymour is a neuroscientist, based at Cambridge University’s Department of Engineering in the United Kingdom. His team recently joined forces with a second group, led by Takufumi Yanagisawa from Osaka University, to examine this problem.
Why does phantom limb pain happen?
One of the major problems with phantom limb pain is that standard pain relief medicine does not remove the discomfort. Dr. Seymour explains that, with this new research, they “wanted to see if we could come up with an engineering-based treatment as opposed to a drug-based treatment.”
The findings, published today in Nature Communications, might be the basis for more effective interventions in the future.
Although the mechanisms behind phantom limb pain remain difficult to unpick, one popular theory is that there is faulty wiring of the sensorimotor cortex. This part of the brain is responsible for processing sensory inputs and executing movements.
Previous research has shown that, following an amputation, there is considerable reorganization of the sensorimotor cortical maps, some of which appears to be maladaptive. It seems that there is a mismatch between a specific movement and the perception of that movement.
To study this possibility and see if these changes could be manipulated, the two teams used a brain-machine interface to decode the mental activity needed for an amputee to “move” their phantom hand. Then, using artificial intelligence (AI) techniques, they turned this information into a signal that moved a robotic neuroprosthetic.
In this way, when a participant attempted to use their phantom hand, they moved a robotic prosthetic.
“We found that the better their affected side of the brain got at using the robotic arm, the worse their pain got. The movement part of the brain is working fine, but they are not getting sensory feedback – there’s a discrepancy there.”
To further investigate this finding, the team switched tactics. They trained the opposite side of the brain. For instance, a patient missing their left arm was trained to move the robotic arm by decoding motions associated with their right arm.
With this reversed training, patients reported a significant reduction in pain. The individuals were making use of the sensorimotor cortex’s natural plasticity – its ability to learn new things by restructuring.
These findings demonstrate a clear link between plasticity in the sensorimotor cortex and pain.
Although these results are certainly positive and offer a new insight into this difficult to understand phenomenon, the reduction in pain was only temporary. Additionally, the process requires a large and expensive set of medical equipment. However, with the rapid advancement of technology, the future of these types of techniques could be bright.
Dr. Seymour hopes that within 5-10 years this new technology might be more easily available, he says:
“Ideally, we’d like to see something that people could have at home, or that they could incorporate with physio treatments. But the results demonstrate that combining AI techniques with new technologies is a promising avenue for treating pain and an important area for future U.K.-Japan research collaboration.”