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They do it with mirrors

Who'd have thought that you could  make the brain pay attention to a useless limb, or even exercise a  phantom one with only a mirror for help, says Helen Phillips

WHEN he woke up in the recovery  room, Bobby Wyatt knew straight away that something was wrong. It  was his right arm. He couldn't see it and he couldn't feel it. Wyatt  panicked--he'd gone in for heart surgery, not amputation.

It didn't take the staff long to figure what had happened--Wyatt had had a stroke during the operation. He couldn't see his arm, because it had slumped off the side of the bed. But he  couldn't feel where it was either, because the stroke had damaged  part of his brain. As far as Wyatt was aware, he'd lost his arm.

Usually we just know what our legs, arms and body  are up to without having to look. We take for granted the powerful impression of a stable, embodied "self". But it's an impression  that's possible only because the brain constructs a "body image" for  us. One important component of that image is a mental map of our  body surface, generated by the cortex, the brain's outer shell, using the touch signals it picks up from the skin. Other components, handled by other parts of the cortex, include the position of our  muscles and joints, the intention to move, and also what we see our body doing.

But, as Wyatt's experience shows, our body image can become distorted, and when it does the disability it causes can be every bit as devastating as injuring part of our body. If a stroke or accident damages the region of the brain housing the body  map, patients may lose the use of a perfectly healthy limb, even though the parts of the brain that directly control movement remain  intact. At the other end of the scale, amputees can have "phantom" limbs, the strong sensation that a limb exists even though they know perfectly well that it doesn't. You can even alter your body image temporarily with a simple trick (see "Try this at home, folks", p 29).

The usual treatments for conditions like these range from stimulating nerves with electrodes to physical therapies such as forced use of the affected limb. Although these treatments can be very effective, they don't work for everyone.

Now a handful of neurologists led by Vilayanur Ramachandran, a neurologist and Director of the Center for Brain and Cognition at the University of California in San Diego, are  developing a new type of treatment that works by beating the brain  at its own tricks. They have found ways to retrain and refashion the distorted body image so that useless limbs can move again and  phantom limbs give up the ghost.

Ramachandran got his inspiration in a roundabout way from a controversial study of monkeys that began more than 20  years ago (New Scientist, 6 July 1991, p 15). A group of monkeys had the sensory nerves from one of their arms severed so they wouldn't feel any sensations from that arm. Eleven years later, when researchers looked at the monkeys' brain activity, they found  that despite the lack of sensory input from the arm, the arm region of the body map in the cortex hadn't gone silent. Instead, signals  from the face--next door on the map--had taken over from the arm ( Science, vol 252 p 1857).

When Ramachandran heard about that study he  instantly thought of a group of his patients who had lost limbs, and  experienced bizarre phantom sensations. Might their body maps have  been rearranged too? With the help of a man who had lost part of his left arm in a car accident--but swore he could still feel  it--Ramachandran soon discovered that his hunch was correct. When he touched the man's face, he said it was as if Ramachandran were touching parts of his missing hand, as well as his face. The whole  surface of the man's hand was mapped out beautifully on his cheek. A second map of the missing arm was inscribed on the stump of the arm.

Those strange sensations are probably the result of  just the sort of changes that happened in the monkeys' brains, says  Ramachandran. When the brain region that had once received messages about physical sensations from the arm suddenly found itself bereft  of input, it compensated by responding to signals from the parts of the body that are mapped next door to the arm--the face and  stump--while still considering them to be from the arm.

What's more, the whole range of feelings had shifted en masse, including differences between cold and hot, light  and heavy touch, vibrations and steady pressure. Ramachandran believes that this is the essence of many a phantom limb. The brain generates the feeling of the limb from the signals coming from another part of the body. So every time Ramachandran's patient smiled or scratched his face, he stimulated the arm region of the  body map.

Transferring sensations of touch and temperature are one thing. But some patients have vivid experiences of movement, spasms, or--even more bizarrely--of paralysis, in their missing  limbs.

Ramachandran suspects that this "learned paralysis"  and the other strange sensations come about in the following way.  Once the limb is severed, the brain continues to send signals telling the missing limb to move. For a while, this creates the  illusion of movement because the brain is still monitoring the  intention. But the patients clearly don't see anything moving, so the different signals feeding into the body image contradict one another. Eventually the brain learns to interpret the lack of response as paralysis.

To treat the paralysis, Ramachandran reasoned that you needed to remove the contradiction by allowing the patient to see the movement they intended to make. He pondered for a while the  practicalities and cost of virtual reality systems, but eventually  hit on a much simpler idea--a mirror.

He placed a large mirror sideways on in front of each patient, so that they saw a reflection of their good arm where the phantom was--just as if the limb had grown back. Next, he asked  them to try making mirror-symmetric movements like conducting an orchestra.

Six of the ten patients instantly felt their "paralysed" phantom limbs moving. Most found the sensation pleasant in itself, and it even enabled a few to shift their paralysed  phantom limbs out of painfully awkward positions.

"A couple of patients we have seen have a clenching  spasm, several times a day," says Ramachandran. With no way to control the painful clenching of a fist that didn't actually exist,  the patients just had to wait for it to pass. "But you put the mirror there and it unclenches instantly," he says.

One amputee did something even more dramatic. He exercised his phantom arm every day for several weeks in front of  the mirror and managed to correct his body image. The phantom gradually shrank and disappeared. "The first example of amputation of a phantom limb," says Ramachandran.

The effect of mirrors on phantoms has yet to undergo the large-scale, placebo-controlled testing that Ramachandran says is necessary, but quite a large number of  neurologists have tried it informally and liked what they've seen. At a meeting on phantom limb pain in Oxford this March, a quick show  of hands revealed that around 30 therapists and neurologists had  tried it with some success.

"The mirror is no universal remedy for all patients  with phantom limb pain," says Peter Brugger, a neurologist at the University Hospital in Zurich. "But we should all use it more, if  only to find out which patients it helps and which it does not."

Learned paralysis may not be limited to phantom  limbs, according to Ramachandran. The monkey studies, and work dating back decades earlier to experiments by Oxford physiologist  Charles Sherrington, show that cutting the sensory signals from the  arm also paralyses it. Though the motor nerves are intact, somehow  the animals need the whole loop of sensory and motor signals to move. Ramachandran wondered whether sometimes the paralysis that often follows a stroke was also learned, possibly when swelling in the brain temporarily restricts nerves, cutting off sensory signals. And if a conflict between the different signals feeding into the  body image was to blame, not permanent physical damage to the nerves, could the mirror help these patients too?

Ramachandran and Eric Altschuler, also at UCSD,  tested the mirror training with nine stroke patients who were left weak on one side--a condition known as hemiparesis. They found that  mirror training seemed to improve the strength and fluidity of movement in at least half of the patients (The Lancet, vol  353, p 2035). Perhaps seeing the arm move--albeit as an optical illusion--compensates for missing sensory input and resolves the conflict.

Krishnankutty Sathian, a neurologist and Medical Director of the Program in Restorative Neurology at Emory University  in Atlanta, Georgia, is also enthusiastic about the potential of  mirror therapy for stroke patients. "We tried a number of patients with the mirror, with not a lot of luck," he says--then Bobby Wyatt  came along. "This particular patient is unusual," says Sathian. "His  problem was motor, he couldn't control the limb. But the main reason  for his problem was sensory loss." Unlike Ramachandran's patients, Wyatt's sensory loss wasn't temporary, but a direct result of the  brain damage from the stroke. "He couldn't feel anything from the right hand, and he couldn't tell where his right hand was in space.  When he was trying to use his hand he had to look at it. He needed  visual input, so we thought the mirror might help."

On reflection

Almost immediately, Sathian noticed that Wyatt's right hand moved a little more fluidly, although Wyatt didn't notice  anything himself for about a week. The mirror made it look as though  he was moving his arm again, but he didn't feel any movement. "Then Dr Sathian told me to look [over the mirror]. I had moved my right  hand," says Wyatt. "It blew my mind. I tell you, at 57 years old, tears came into my eyes."

Sathian and his colleagues believe that the mirror helped Wyatt learn to use non-standard sensory cues, such as the  sensations from the upper arm, as well as vision, to substitute for the normal, fine-grained sensory map.

But few treatments are without side effects, even  mirror therapy. Once he started moving his right arm, Wyatt found that it would sometimes tag along with the left, without him intending it. Now, after more than a year and a half of training every day with the mirror--he even set one up at home--he's learned  to control his arm more independently. "I even took my driver's test  a few months ago," says Wyatt.

So useful is mirror therapy looking, that  Ramachandran has even tried it out with a small number of patients with a rare and notoriously difficult to treat condition known as  hemispatial neglect, which happens after a particular type of right  brain stroke. Not only are these patients often paralysed on their left side, they are also completely unaware of anything to their left--even the paralysis. By putting a mirror on the patients' right, so they could see the normally neglected left side reflected  to their right, Ramachandran hoped he could reverse that condition. "The question is, if you put a mirror on the right, will it somehow  enable them to suddenly pay attention?" he asks.

Results have been mixed so far. In some patients,  things seem to get even more confused. "They start reaching into the  mirror," he says. But a couple of patients actually reach over to the left with their unparalysed arm when the mirror is there,  seemingly aware again of their neglected side. The acid test will be  if repeated practice with the mirror eventually helps them pay  attention to their left when the mirror is gone. "At the moment it's  still a maybe," says Ramachandran.

Ramachandran, Sathian, and others say they wouldn't  be too surprised if one day a simple mirror becomes routine therapy for a host of conditions in which the brain's ability to sense and represent the body causes a physical disability.

"I don't like to go around touting miracle cures," says Ramachandran. "You don't want to give false hopes." On the other hand, he says, such a straightforward treatment is unlikely to do any harm. "At best, you have a procedure that genuinely works in some patients," says Ramachandran. "At the very least, you have the world's least expensive, most effective placebo."

Further reading: Phantoms in the Brain by Vilayanur Ramachandran and  Sandra Blakeslee (Fourth Estate, 1998) "Doing it with mirrors: a case study of a novel approach to neurorehabilitation" by Krishnankutty Sathian and others,  Neurorehabilitation and Neural Repair, vol 14, p 85 (2000) "Consciousness and body image: lessons from phantom  limbs, Capgras syndrome and pain asymbolia" by Vilayanur  Ramachandran, Philosophical Transactions of the Royal  Society of London B, vol 353, p 1851 (1998)

Try this at home, folks There are a few simple illusions that  demonstrate the amazing malleability of the brain's image of the body. One trick is to sit at a table and recruit a helper. Hide one hand under the table, resting palm down on your knee. Then ask your helper to tap, touch and stroke with their  fingertips the back of your hidden hand and the table top directly above the hand with an identical pattern of  movements, for a minute or two. It's important that you concentrate on the table, where your helper is touching, and that you can't see  your hand or their hand under the table. The more irregular the pattern, and the more synchronised the touches you can see  and feel, the more likely you are to feel something very strange. About half the people who try this find that the  table starts to feel like part of their body--as though the hand is transferred into the table. "What this is telling you is that the brain's  body image is amazingly plastic," says Vilayanur Ramachandran from the University of California in San Diego. "You've grown  up with this body and yet the table gets assimilated into your  body image." Just as an amputee might experience a phantom limb, says Ramachandran, our entire body image is a  phantom--something the brain constructs for  convenience. From New Scientist magazine, 17 June 2000.

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