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