One theory of phantom limb pain is that the sensorimotor cortex of the brain that is responsible for sensing and moving the hands, arms, and legs becomes confused by the sudden loss of a limb. The brain senses a mismatch between its attempt to move the limb and the feedback it receives, and interprets that mismatch as pain. A study, published October 27 in Nature Communications, describes the use of brain-machine interface (BMI) training to dissociate a prosthetic hand and an amputated hand or a hand affected by severe nerve damage to reduce phantom limb pain-the associated pain in the nerve-damaged hands is thought to share a common mechanism with phantom limb pain due to amputation The BMI training technique essentially involves distracting the brain from mixed signals it may receive as a result of losing the limb, said co-author Ben Seymour, MBChB, MRCP, PhD, a neuroscientist with the Department of Engineering at the University of Cambridge, England. He said the BMI training method may provide an alternative to pain medications for people who experience phantom limb pain.
The research team included Seymour and researchers from Osaka University, Japan. They trained ten people with phantom limb pain symptoms to control a robotic arm using their brain activity. Nine participants had brachial plexus root avulsion and one had a transradial amputation.
The BMI used real-time magnetoencephalography signals to reconstruct the movements of the affected hand with a robotic hand. The BMI training induced significant plasticity in the sensorimotor cortex, manifested as improved discriminability of movement information and enhanced prosthetic control, according the researchers. The team used the BMI to decode the neural activity of the mental action needed for a patient to move his or her amputated or nerve damaged hand, and linked those signals to a robotic prosthetic limb.
The participants performed an offline task (pre-BMI) in which they were instructed to try to move their affected hands to be in the posture of grasping or opening according to given instructions; they could not see their sound side arms during the experiment. For comparison, the participants performed actual movements of their intact hands following the same instructions.
Patients experienced an increase in phantom limb pain if they tried to control the prosthetic arm by willing the movement of their affected arms. However, the researchers discovered that the phantom limb pain decreased if the participants were trained to move the robot arm using the “wrong” side of their brains. For example, patients with affected left arms experienced reduced pain if they moved the prosthetic arm through neural signals associated with their right arms. The results reveal a functional relevance between sensorimotor cortical plasticity and pain, and may offer a novel treatment with BMI neurofeedback, according to the study.
