A simple, inexpensive device that delivers electrical current to the brain noninvasively could help stroke patients recover lost motor ability. According to a new study, the treatment–transcranial direct current stimulation (tDCS)–in combination with occupational therapy boosted recovery better than either treatment on its own.
Many patients spontaneously recover some function in the weeks and months after suffering a stroke, as their brains reorganize to compensate for the damaged area. Scientists are searching for ways to both boost and focus this innate plasticity, thus improving neural repair. Electrical activity is one option under study: electrical current applied to the brain can modulate brain-cell activity–a crucial component of neural remodeling.
In tDCS, an electrical current is passed directly to the brain through the scalp and skull. (The treatment generates just a slight tingle, if anything, in the patient.) Previous research has shown that applying tDCS to the motor cortex can improve motor performance in healthy people and, to some extent, in stroke patients. But most previous studies have tested just a single treatment, and few have used it in conjunction with rehabilitation exercises.
In the current study, Gottfried Schlaug and his collaborators at Beth Israel Deaconess Medical Center, in Boston, tested 20 patients who had suffered a stroke an average of 2.5 years previously and still had moderate to severe impairments. Patients performed 60 minutes of occupational therapy each day for five days, while also receiving a 30-minute session of either active electrical stimulation or a placebo–a fake treatment designed to mimic electrical stimulation.
The researchers used a simple device–a nine-volt battery connected to large flat sponges that are moistened and then applied to the head–that has been approved by the Food and Drug Administration for delivering drugs across the skin. (The current encourages the movement of charged drug molecules across the skin.)
A week after the start of the experiment, patients given the real treatment performed much better on a number of motor tests–including tests of strength, range of movement, and practical functions such as grasping a cup–than those who received the fake treatment, improving by about 12 to 15 percent versus about 3 to 5 percent, says Schlaug. He presented the research at a conference in San Francisco this week sponsored by the Organization for Human Brain Mapping.
Using functional magnetic resonance imaging (fMRI), the researchers also found that activity in the injured part of the brain increased after the course of treatment.
While it’s not yet clear exactly how tDCS improves motor function after stroke, one theory is that it helps repair an imbalance in the interactions between the two hemispheres of the brain. In the healthy brain, the left and right sides of the motor cortex continually inhibit each other in order to carry out one-sided movements, such as writing or brushing one’s teeth. If one side is damaged by stroke, it can no longer effectively inhibit the healthy side, which in turn leads to increased inhibition of the stroke-damaged hemisphere. “There is some thought that this imbalance of inhibition actually hinders stroke recovery,” says Schlaug. “Noninvasive brain stimulation offers a potential solution to this, or at least a way to test this hypothesis.”