After a stroke has done its worst, killing brain cells by cutting off or drastically reducing their blood supply, healthy cells will often fill the functional breach. But what’s the best way to encourage them? Last June, neurobiologist Randolph Nudo and his colleagues at the University of Texas Health Science Center published a study suggesting that physical therapy is just as effective as drug therapy after a stroke.
Using a microelectrode probe, the researchers stimulated neurons in the motor cortices of 13 adult squirrel monkeys, precisely mapping the areas responsible for limb movement. Then in 9 of the monkeys they mimicked strokes by creating small lesions in a region of the brain that partially controls the hand. In the month that followed, 4 of the 9 monkeys were retrained in fine motor skills with a repetitive exercise--they practised extracting pellets from cylindrical wells with their fingers. The other 5 monkeys with lesions received no rehabilitation. (The 4 monkeys without lesions were a control group.)
All 13 monkeys again underwent the cortical mapping procedure. There was a tremendous amount of remodeling going on, says Nudo. It would appear that rehabilitation encouraged the surrounding tissue to take over the damaged area’s function and even to expand into the elbow and shoulder areas. But monkeys without retraining had the opposite experience. The hand area of their cortex actually shrank as it was invaded by its neighbors. While untrained monkeys did eventually recover basic motor ability, Nudo explains, they seem to have done it more slowly; they had to learn new ways to compensate for their loss of mobility, whereas the monkeys who did the repetitive exercises actually relearned the old motor skills. Says Nudo: It’s only if you’re forced to perform those functions that you actually regain them.