What phantom limbs and mirrors teach us about the brain

In a lab in southern California scientists are curing the previously incurable with little more than a mirror, and changing our understanding of the brain in the process.

In mid-November the team at the University of California San Diego (UCSD) announced the results of a small pilot study which suggests that a simple mind trick involving mirrors can help ease the pain of osteoarthritis, a condition that affects one in 10 people.

That study is in its very early stages, but since the mid-1990s neuroscientist Vilyanur S Ramachandran, who heads the team, has been extolling the benefits of mirrors for all manner of diseases and syndromes, from stroke to the mind-boggling medical phenomenon of the phantom limb.

Ramachandran's 20-year association with the mirror, and phantom limbs, has driven him to the forefront of experimental neuroscience.

The syndrome occurs in at least 90% of amputees - in two-thirds of those it manifests as an insatiable itch in the missing limb, many feel extreme discomfort or even chronic pain.

In most cases, pain-killers and surgical treatment have no effect.

Ramachandran's first phantom limb patient - who he calls Victor - lost his arm crossing the Mexican border into the US. He had an itch in his missing hand.

When Ramachandran prodded him in the left cheek with a cotton bud, Victor claimed he felt it in his missing left thumb - when he touched his upper lip, Victor though he was prodding his index finger.

The neurons that detect sensation in the missing hand, at a loss for anything to do, had somehow started detecting sensation in the face.

In this case there was a simple and effective treatment for the itch - scratch the face. But to Ramachandran it also had theoretical implications. It appeared to demonstrate the plasticity of brain modules - their ability to adapt to each other and their environment.

This was a radical idea as the established notion at the time was that the brain is made up of independent modules, insulated from each other and hardwired to a specific function. The notion of plasticity was something only a small group of scientists were considering.

In 1994, Ramachandran proved the theory by mapping the brain activity of a group of amputees. Using a magnetic scanner he showed that neuron activity was indeed migrating from the hand area to the face. It was a ground-breaking study.

But he believed much more could be gleaned from studying phantom limbs.

In the mid-1990s he followed the work of Italian scientist Giacomo Rizzolatti, who discovered an entirely new type of neuron that he called the mirror neuron.

Rizzolatti observed that certain neurons in the brain of a macaque monkey fired when the monkey reached out and when it watched another monkey reach out. Mirror neurons were later discovered in humans too.

Ramachandran began to apply this finding to his work with phantom limbs. If mirror neurons fired when an individual watched someone moving a limb, he conjectured, then visual perception might play an important role in creating the sensation of movement.

His next subject, Jimmy, felt that his phantom hand was always agonisingly clenched, with his phantom fingernails digging into his missing hand.

Ramachandran put a mirror between Jimmy's arms and asked him to move both his phantom and healthy limb simultaneously, while looking at the reflection of the healthy limb - effectively fooling Jimmy's brain into thinking his phantom was moving in a normal way.

Jimmy felt his clenched fist release almost immediately.

"This is because you are creating intense sensory conflict - the vision is telling you the limb is moving," Ramachandran explains.

"One way the brain deals with conflict is to say, 'To hell with it! There is no arm,' and the arm disappears.

"I tell my medical colleagues that it is the first example in the history of medicine of successful amputation of a phantom limb."

He called the treatment Mirror Visual Feedback therapy or MVF. But it wasn't until much later that MVF was properly acknowledged by clinicians.

In 2007, an army medic in the US Dr Jack Tsao, performed a controlled test on 22 amputees with remarkable results. All those using the mirror reported a reduction in pain over four weeks, those using a control reported no result or increased pain.

At the UK army's rehabilitation centre, Hedley Court, mirror therapy has also been used for the past four years to help amputee soldiers to manage phantom pain.

"Prosthesis-wearing is key," says army physiotherapist Major Pete LeFeuvre. Those who wait longer for a fake limb seem to suffer more from phantom pain. This suggests it is the visual feedback of seeing an arm rather than the feedback from nerves within it that stops the brain getting confused.

In Vietnam, a project called End the Pain has been running for the past three years to spread the therapy among victims of landmines and leprosy sufferers. It has reached over 100 medical practitioners so far and has also extended the project to amputees in Cambodia and Rwanda.

The simple therapy has proven useful with other syndromes that have perplexed doctors such as Complex Regional Pain Syndrome, a term for unexplained pain. And at the Royal National Hospital for Rheumatic Diseases in the UK, an associate of Ramachandran, Professor Candy McCabe is testing the use of mirrors with acute stroke victims.

Though it is in its very early stages, the experiment into arthritis at UCSD could provide the broadest use of mirror therapy yet.

Much of Ramachandran's work since developing mirror therapy has focused on mirror neurons. He believes these neurons help us understand not only what is happening to our own body, but also to others. They are the basis of empathy, he suggests, our ability to feel what others feel.

In 2009 he used the phantom limb again to provide evidence for this theory, showing that sufferers could experience relief from phantom pain merely by watching someone else massaging or flexing their own hand.

While others spend million on machines with complicated acronyms, the beauty of Ramachandran's work is that he uses ordinary items such as mirrors, pens and paper.

"The hi-tech stuff is very important but it lacks the aesthetic appeal of the other stuff," he says.

"It has the slightly boring, banal quality to it."

Find out more about VS Ramachandran's work on Exchanges at the Frontier, external from the BBC World Service in association with the Wellcome Collection. Listen to the programme here.