Mirror Therapy Alters Brain Response in Phantom Limb Patients

Neuroimaging Could Help Tailor Treatment for Amputees

By Brandon Levy

Tuesday, July 23, 2019

Our brains frequently cause us to perceive things that are not real, from high-pitched ringing in an empty room to dancing spots in our vision after staring at a bright light. Even more strangely, people with phantom limb syndrome feel sensations, including pain, in arms and legs that they no longer have. New IRP research into the brain mechanisms underlying phantom limb pain could help hone treatment for individuals living with the condition.¹

Studies suggest that the vast majority — perhaps over 90 percent — of amputees experience phantom limb pain.² Pain medications do little to relieve these sensations, making effective treatment difficult.

“It’s very challenging for these patients,” says Annie Chan, Ph.D., the new study’s first author and a former IRP postdoctoral fellow who is now an assistant professor at Brunel University in London. “I was very close to the patients that I worked with. They would come for a physical and I would talk to them for hours and they would describe every painful element."

While the underlying reason why phantom pain occurs remains controversial, there is increasing scientific consensus that a treatment called mirror therapy can benefit some people with the condition. Mirror therapy requires the patient to move his or her unaffected arm or leg while observing the movement in a mirror, which creates the visual illusion that the missing limb on the other side of the body is moving. Unfortunately, the treatment does not work for every patient.

Dr. Chan gathered the data for the new study while working in the lab of the paper’s senior author, IRP senior investigator Chris Baker, Ph.D. Nine leg amputees who had developed phantom limb pain viewed images of hands and feet while undergoing a functional magnetic resonance imaging (fMRI) brain scan to measure activity in different parts of their brains. They then began a four-week course of mirror therapy and had their brains scanned again two weeks and four weeks after the first scan while viewing the same hand and foot images. Nine healthy individuals of the same genders and roughly the same ages as the amputees also completed the same brain scanning regimen but did not complete mirror therapy.

Compared to the healthy participants, the amputees had much more activity in a part of the brain called the sensorimotor cortex when they saw images of feet during their first two fMRI scans. This brain area was also much more active when the patients viewed foot images than when they viewed hand images, a difference that was not seen in the healthy participants. However, during the final fMRI scan — completed after the patients had undergone four weeks of mirror therapy — the amputees’ brain responses to both hand and foot images looked identical to those of their healthy counterparts.

Moreover, not only did mirror therapy lead to a significant decrease in the patients’ phantom limb pain, but the patients who had the most brain activity in the sensorimotor cortex while viewing images of feet during the first fMRI scan experienced the largest reductions in pain by the end of the study. If additional, larger studies can replicate this finding, fMRI scans that measure activity in the sensorimotor cortex could be used to identify patients with phantom limb pain for whom mirror therapy is most likely to be effective.

“Some people benefit from mirror therapy and some don’t, and the mechanism underlying phantom limb pain may not be identical in those two groups,” Dr. Baker says. “Mirror therapy may be a good option for certain people, but for others there may be another type of treatment that would be more useful.”

Since pain and activity in the sensorimotor cortex did not decrease at the same rate in the patients who participated in mirror therapy, it remains uncertain whether the two findings are causally linked. Future studies will also need to confirm that the results generalize to arm and hand amputees, as well as include a control group of patients who do not participate in mirror therapy in order to ensure that the therapy caused the reduced pain and brain activity.

“These kinds of studies provide a route into treatment,” Dr. Baker says. “Having an idea of the neurological mechanism underlying phantom pain gives you a way to think about what treatments might be helpful.”

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References:

[1] Visual responsiveness in sensorimotor cortex is increased following amputation and reduced after mirror therapy. Chan AW, Bilger E, Griffin S, Elkis V, Weeks S, Hussey-Anderson L, Pasquina PF, Tsao JW, Baker CI. Neuroimage Clin. 2019 May 30;23:101882. doi: 10.1016/j.nicl.2019.101882.

[2] Phantom pain, residual limb pain, and back pain in amputees: results of a national survey. Ephraim PL, Wegener ST, MacKenzie EJ, Dillingham TR, Pezzin LE. Arch Phys Med Rehabil. 2005 Oct;86(10):1910-9. doi: 10.1016/j.apmr.2005.03.031.

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