DALLAS, June 2 - Researchers have shown for the first time in humans that rehabilitation therapy may help a stroke survivor's brain rewire itself, leading to regained use of a previously unused limb. The study is in this month's Stroke: Journal of the American Heart Association.
"This result has been a goal in neuroscience for decades, and while it has been shown in animals, it's the first time it's been shown for humans," says one of the study's authors, Edward Taub, Ph.D., of the University of Alabama at Birmingham.
For decades it was believed that once brain cells died after a stroke, they were gone forever. Recent research is finding that the brain is much more "plastic" than previously thought. "Plasticity" refers to the brain's capability to rewire its circuitry to perform tasks that it was incapable of doing because of a severe injury.
This finding offers hope to researchers who believe that it may be possible to stimulate or manipulate brain areas to take over the lost functions, a process known as cortical reorganization.
Researchers used a procedure called focal transcranial magnetic stimulation to map the activity of the cerebral cortex, the thin layer of gray substance covering the surface of each hemisphere of the brain. The cerebral cortex is involved in higher mental functions, and in the production of general movement and behavioral reactions.
In particular, Taub and his colleagues monitored the area of the cortex that controls an important hand muscle, comparing the activity in the injured part of the brain with the unaffected portion. They examined 13 stroke survivors - 10 men, three women - before and after a 12-day period of movement therapy.
"The bottom line is that our rehabilitation technique recruits additional areas of the brain to participate in the production of movement after stroke," says Taub.
Before treatment, the area of the cerebral cortex controlling movements of the hand muscle was considerably smaller on the damaged side of the brain than on the non-affected side. After treatment, the size of the active area capable of generating movement in the damaged hemisphere was significantly enlarged, corresponding to a greatly improved motor performance of the hindered arm.
"These results show the potential for the improvement of impaired function after neurological injury by the use of appropriate techniques," says Taub. "This also opens the possibility of being able to produce this effect by other rehabilitation therapies or by pharmacological means."
In follow-up examinations up to six months after therapy, brain activity remained at a high level and the area of activity in the two hemispheres became almost identical. The improved motor function also persisted over this period of time.
The treatment, called constraint-induced movement therapy, involves restraining of the arm less affected by the stroke for 90 percent of waking hours for two or three weeks. On the weekdays during the period, six hours of therapy are interspersed over seven hours, with one hour of rest. The effectiveness of this therapy, according to Taub, results from the fact that it requires the continual use of the affected extremity for many hours a day during a period of consecutive weeks.
One day before treatment, the patients scored an average of 2.2 on a test that tracked arm use in 20 common and important activities of daily living and an average of 3.7 one day after treatment. A score of 2 indicates slight use; 3, half as much use as before stroke; and 4, three-fourths as much use as before stroke.
By the first day after treatment, there was 37.5 percent more activity in the damaged part of the brain than in the healthy part of the brain. This represented a near-doubling of the active area of the brain on the affected side.
According to Taub, the reorganization reflects either an increase in the excitability of neurons already involved in the development of affected hand movements, an increase in the amount of excitable tissue in the damaged hemisphere, or both.
Co-authors are Joachim Liepert, M.D.; Heike Bauder, Ph.D.; Wolfgang H.R. Miltner, Ph.D.; and Cornelius Weiller, M.D.
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