麻豆传媒

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

It didn鈥檛 take the staff long to figure what had happened鈥擶yatt had had
a stroke during the operation. He couldn鈥檛 see his arm, because it had slumped
off the side of the bed. But he couldn鈥檛 feel where it was either, because the
stroke had damaged part of his brain. As far as Wyatt was aware, he鈥檇 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 鈥渟elf鈥�.
But it鈥檚 an impression that鈥檚 possible only because the brain constructs a 鈥渂ody
image鈥� for us. One important component of that image is a mental map of our body
surface, generated by the cortex, the brain鈥檚 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鈥檚 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 鈥減hantom鈥� limbs, the
strong sensation that a limb exists even though they know perfectly well that it
doesn鈥檛. You can even alter your body image temporarily with a simple trick (see
鈥淭ry this at home, folks鈥�).

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鈥檛 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 (麻豆传媒, 6
July 1991, p 15). A group of monkeys had the sensory nerves from one of their
arms severed so they wouldn鈥檛 feel any sensations from that arm. Eleven years
later, when researchers looked at the monkeys鈥� 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鈥檛 gone silent. Instead, signals from the face鈥攏ext door
on the map鈥攈ad 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鈥攂ut swore he could still feel
it鈥擱amachandran soon discovered that his hunch was correct. When he
touched the man鈥檚 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鈥檚 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鈥� 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鈥攖he face and
stump鈥攚hile still considering them to be from the arm.

What鈥檚 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鈥檚 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鈥攅ven more
bizarrely鈥攐f paralysis, in their missing limbs.

Ramachandran suspects that this 鈥渓earned paralysis鈥� 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鈥檛 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鈥攁 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鈥攋ust 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 鈥減aralysed鈥� 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.

鈥淎 couple of patients we have seen have a clenching spasm, several times a
day,鈥� says Ramachandran. With no way to control the painful clenching of a fist
that didn鈥檛 actually exist, the patients just had to wait for it to pass. 鈥淏ut
you put the mirror there and it unclenches instantly,鈥� 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. 鈥淭he first example of
amputation of a phantom limb,鈥� 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鈥檝e
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.

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

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鈥攁 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鈥攁lbeit as an optical
illusion鈥攃ompensates 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. 鈥淲e
tried a number of patients with the mirror, with not a lot of luck,鈥� he
says鈥攖hen Bobby Wyatt came along. 鈥淭his particular patient is unusual,鈥�
says Sathian. 鈥淗is problem was motor, he couldn鈥檛 control the limb. But the main
reason for his problem was sensory loss.鈥� Unlike Ramachandran鈥檚 patients,
Wyatt鈥檚 sensory loss wasn鈥檛 temporary, but a direct result of the brain damage
from the stroke. 鈥淗e couldn鈥檛 feel anything from the right hand, and he couldn鈥檛
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
丑别濒辫.鈥�

On reflection

Almost immediately, Sathian noticed that Wyatt鈥檚 right hand moved a little
more fluidly, although Wyatt didn鈥檛 notice anything himself for about a week.
The mirror made it look as though he was moving his arm again, but he didn鈥檛
feel any movement. 鈥淭hen Dr Sathian told me to look [over the mirror]. I had
moved my right hand,鈥� says Wyatt. 鈥淚t blew my mind. I tell you, at 57 years old,
tears came into my eyes.鈥�

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鈥攈e even set one up at home鈥攈e鈥檚
learned to control his arm more independently. 鈥淚 even took my driver鈥檚 test a
few months ago,鈥� 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鈥攅ven the
paralysis. By putting a mirror on the patients鈥� right, so they could see the
normally neglected left side reflected to their right, Ramachandran hoped he
could reverse that condition. 鈥淭he question is, if you put a mirror on the
right, will it somehow enable them to suddenly pay attention?鈥� he asks.

Results have been mixed so far. In some patients, things seem to get even
more confused. 鈥淭hey start reaching into the mirror,鈥� 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. 鈥淎t the moment it鈥檚 still a maybe,鈥� says
Ramachandran.

Ramachandran, Sathian, and others say they wouldn鈥檛 be too surprised if one
day a simple mirror becomes routine therapy for a host of conditions in which
the brain鈥檚 ability to sense and represent the body causes a physical
disability.

鈥淚 don鈥檛 like to go around touting miracle cures,鈥� says Ramachandran. 鈥淵ou
don鈥檛 want to give false hopes.鈥� On the other hand, he says, such a
straightforward treatment is unlikely to do any harm. 鈥淎t best, you have a
procedure that genuinely works in some patients,鈥� says Ramachandran. 鈥淎t the
very least, you have the world鈥檚 least expensive, most effective placebo.鈥�

There are a few simple illusions that demonstrate the amazing malleability of
the brain鈥檚 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鈥檚 important that you concentrate on the table, where your helper is
touching, and that you can鈥檛 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鈥攁s though the hand is transferred into the table.

鈥淲hat this is telling you is that the brain鈥檚 body image is amazingly
plastic,鈥� says Vilayanur Ramachandran from the University of California in San
Diego. 鈥淵ou鈥檝e grown up with this body and yet the table gets assimilated into
your body image.鈥� Just as an amputee might experience a phantom limb, says
Ramachandran, our entire body image is a phantom鈥攕omething the brain
constructs for convenience.