Evidence found mirror box therapy alleviates phantom limb pain in amputees

Mirror box therapy involves an amputee placing a healthy limb on one side of a mirror box, and a stump on the other. Photo / Getty Images

An investigation by a team of Kiwi researchers has found solid evidence to back an intriguing approach used to alleviate phantom limb pain in amputees.

Professor Liz Franz and colleagues at Otago University have published studies pinpointing the neural responses in the brain that might indicate why "mirror box therapy" has shown encouraging results among patients who have used it.

The technique, credited to renowned US neuroscientist Professor Vilayanur S. Ramachandran, involves an amputee placing a healthy limb on one side of a mirror box, and a stump on the other.

When the patient looks at the mirror's reflection and moves their healthy limb, it also appears as if the phantom limb is also moving, and the illusion helps the brain move the phantom limb out of painful "positions".

Scientists point to the fact that when one hand moves, the motor cortex on the opposite side of the brain becomes active.

Mirror box research suggests that when a patient sees the reflection of their left hand moving by use of a mirror - making it look like their right hand - the left motor cortex is activated as well.

In her lab, Franz has been working with PhD student Ranjan Debnath and a team of researchers to investigate the nature of the effect, which has been surrounded in debate by scientists.

Because there has been increasing interest in using it as a therapy for amputees - and more recently for sufferers of unilateral stroke - it was important to clearly establish whether the activation occurred on the same brain side to a moving hand could be quantified in a reliable and meaningful way.

In a recently published investigation, the Otago researchers recorded continuous EEG readings of neural activity of study participants, while they measured movements of their arms and hands.

In a further study, published recently in the journal Restorative Neurology and Neuroscience, the researchers again looked closely at the mirror box approach.

They introduced a foot pedal into the research method so that at the precise point where the participant felt like the mirror image was their actual hand, they would tap the foot pedal.

This allowed researchers to align the perception with the EEG reading for that moment -- and control conditions were used to remove any other influencing factors from the picture.

"Other studies have used fMRI to localise brain activation when examining these types of issues, but the EEG paired with the foot pedal methodology allows us to match the perception and the brain activity in time," Franz said.

"Capturing precise brain changes in association with perceptions of movement seems critical in any therapeutic developments using the mirror box."

Franz said the findings were exciting - and prompted many more questions.

"We are getting motor activations with a perception of a movement via a mirror reflection, which I think is quite interesting," she said.

"You can imagine a scenario where a person is paralysed and can't move at all, but may still have quite a vivid perception of movement - and if we could then activate the motor areas in their brain, that could be super helpful."

Although there was still much to learn about the brain networks involved in mirror box treatment, the studies had shown the effects appeared to have been immediate.

"We felt it was pretty solid stuff," Franz said of the findings.

She was now curious to see whether the same effects could be observed in impaired brains - particularly those that had been affected by stroke.