The technique, called repetitive transcranial magnetic stimulation (rTMS), had beneficial effects lasting at least two weeks, according to the report published Thursday in the journal Stroke.
"The results are certainly encouraging, but what the clinical implications are at this point is really unclear," said Dr. Larry Goldstein, director of the stroke center at Duke University in Durham, N.C., and chairman of the American Stroke Association's stroke council.
Because the study was small and relatively short, "We don't know at this point what the patients will be like six months or a year from now," he said.
Goldstein was not involved in the study, which was conducted by a team at Harvard Medical School and Beth Israel Deaconess Medical Center in Boston.
According to lead researcher Dr. Felipe Fregni, rTMS seeks to slow activity in the side of the brain unaffected by stroke. In that sense, the treatment works on the same principle as "constraint-induced therapy" -- a successful rehabilitation strategy where a stroke survivor's healthy limb is restrained, forcing the affected limb to function better.
Researchers elsewhere are investigating the use of rTMS for a number of neurological conditions. Previous work on stroke paved the way for the current trial, Fregni said.
"We know that several sessions of rTMS can increase the magnitude and duration of the beneficial effects, so we assessed the effect of five sessions," Fregni said in a prepared statement.
The trial included 15 people who had suffered strokes at least a year earlier. Ten got rTMS treatment to ease activity in the motor cortex area of the undamaged hemisphere of the brain. The other five patients got a sham treatment.
Testing reaction time of the patient's stroke-affected hands, the researchers found that those who got rTMS got 30 percent faster after five days of treatment. This effect lasted for two weeks, they said. The improvement increased early as the number of treatments increased. Patients were, on average, 10 percent, 20 percent, 27 percent and 30 percent faster on days two, three, four and five of treatment, respectively, Fregni noted.
Goldstein said that although these motor improvements look promising, it's still unclear whether they will translate into better long-term physical performance, he said. "We need studies for a longer period of time with measures of the [patients'] quality of life," Goldstein said.
Studies of rTMS and stroke are also under way at the Emory University School of Medicine in Atlanta, said researcher Andrew J. Butler, an assistant professor of rehabilitation medicine at that institution.
"We have a slightly different perspective," Butler said. "They are using it on the unaffected hemisphere in hopes it will reduce the amount of damage. We are using it in conjunction with physical constraint therapy. We use excitatory pulses into the affected hemisphere," he said.
The Emory group's work with stroke patients has not yet been submitted to a medical journal for publication, Butler said.
In another hopeful development, researchers at the U.S. National Institute of Neurological Diseases and Stroke reported that they had stimulated the growth of new brain cells in rats after a stroke. The researchers said they used a protein to activate the stem cells, setting off a cascade effect that created new brain cells. Many rats given the treatment regained the function they lost after the stroke, the researchers reported in the journal Nature.