Much has been written about the amazing ability of the
damaged human brain to rewire itself. Research has shown
that an undamaged hemisphere will often adapt to take
on tasks previously performed by the other side. In stroke
victims, this is one of the principal mechanisms of recovery.
This raises a fascinating possibility — could it
be that temporarily suppressing activity on the undamaged
side of a stroke victim's brain might help restore function
to the damaged hemisphere?
Apparently, it could. A team of
researchers from Harvard and the University of Sao Paulo
have reported in the May 24 edition of Neurology
that repetitive transcranial magnetic stimulation (rTMS)
of stroke victims' brains produced dramatic improvements
in motor control and reaction time tests.
The term "stimulation" is something
of a misnomer, since the immediate effect of the magnetic
field is not to stimulate, but to suppress neuronal
activity in the targeted region of healthy tissue. But
the ultimate purpose is to stimulate activity in the
parts of the brain touched by stroke.
This procedure was successfully
tried last year in patients who'd suffered a left frontal
stroke. Now, for the first time, the treatment has been
applied to patients with motor deficits following stroke.
The trial was small, involving just 10 patients, half
of whom underwent real magnetic stimulation while the
other half were given sham treatment. But the improvement
in test scores was large enough to yield fairly robust
statistical power. Not only did the rTMS recipients
outperform the sham treatment recipients by 50%, they
also dramatically improved their own pre-treatment scores
in a range of simple and choice reaction tests.
SHORT
BUT SWEET SUCCESS
Unfortunately, the improvement was short-lived. "The
effect only lasted for about an hour," admits lead author
Dr Felipe Fregni of Harvard Medical School. "But that
is what we expected. It takes a course of treatments
to achieve a lasting effect."
In fact, so pressing was the need
to measure subjects' reactions immediately after rTMS
that the investigators had no time for the brain imaging
studies that could have confirmed their primary hypothesis
— that intercallosal signalling between the two
hemispheres triggers each side to take up the slack
when its companion is underperforming.
"Clearly, we need to confirm these
results in a bigger study," acknowledges Dr Fregni.
"We're currently recruiting 60-80 subjects for a new
study. We hope to learn more about the mechanism of
action, and above all to look at the effects of repeated
therapy."
There's evidence that the hard-wiring
of the brain does change with repeated magnetic stimulation,
as damaged pathways are rebuilt or replaced. Dr Fregni
compares it to piano lessons: "If you practice for one
afternoon, a week later you will have forgotten how
to play. But if you practice regularly enough, eventually
it becomes second nature."
"I don't think we'll ever achieve
a truly permanent effect, but after an initial course
of regular treatment, patients might be able to get,
say, one treatment a month. That could feasibly provide
lasting benefit."
Neurology May 24, 2005;64:1802-4
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