Rewiring the brain after a stroke
Stroke victims are often left incapacitated, unable to speak clearly, walk without assistance or do routine tasks such as grooming and feeding themselves. Because current physical therapy can go only so far in restoring lost abilities, many of them must learn to accept their new limitations.
An experimental device may eventually be able to help such patients resume relatively normal lives. By electrically stimulating injured brain regions, it appears to reverse some of the physical damage of stroke.
“This is an important advance,” says Dr. Robert Levy, a neurosurgeon at Northwestern Memorial Hospital in Chicago who has tested the electrical stimulator. “This has significant potential for improving the quality of life for a large number of people.”
The device, similar to a cardiac pacemaker, consists of electrodes that are attached by a wire to a pulse generator, which transmits electrical signals to the affected area of the brain.
To determine precisely where to place the system, doctors perform a functional MRI test to reveal the injured part of the brain. Surgeons then open the skull and place the thumbnail-sized electrode on the surface of the brain, or cortex, at the spot that controls movement of the affected arm, wrist or hand. The electrode’s wire is threaded under the skin, through the neck, and is hooked up to the battery-powered pulse generator, implanted under the collarbone.
Experts aren’t sure of the mechanism, but they say the resulting brain stimulation promotes recovery of motor function. “The brain does change in response to external stimulation,” says Brad Gliner, a biomedical engineer at Northstar Neuroscience Inc. in Seattle who helped develop this technology.
Results of a recent test of 24 stroke victims were encouraging. Half received the electrical implants and aggressive rehabilitation therapy; the other half received only the rehabilitation therapy. After six weeks, patients with the cortical stimulator experienced a 7.8-point improvement in hand and arm movements, according to motor function tests, compared with a 3.7-point increase in the control group. A 3-point improvement is considered clinically meaningful.
Stroke is the leading cause of long-term disability in the United States, and more than 200,000 Americans each year become debilitated. Although stroke victims often spontaneously regain some motor control in the first three or four months after their stroke, most people plateau after that, and some even lose ground once they stop rehabilitation therapy.
“These were people who were two to three years out from their strokes and they weren’t getting better, so it’s remarkable the therapy worked at all,” says Levy.
The electrical stimulation, in combination with the movement provided by traditional therapy, seems to either jump-start the growth of new nerve fibers or reorganize nerve cells in the area of the stroke so that other cells take over the function of the ones that died, says Gliner. And although the initial study focused on improving arm, wrist and hand movements, this approach could also be used to improve motor function in the legs and treat other stroke deficits such as speech difficulties, he says.
Northstar Neuroscience recently launched a larger clinical trial that will eventually involve 100 patients. The company hopes to have the stimulator available to the general public within the next three years.
“But we’re still just stabbing in the dark on the best way to stimulate the brain based on what we know from experiments in animals,” Levy says. “Once we learn more about how this works, we’ll likely see much greater improvements.”
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Shocks to the nervous system
Deep brain stimulators, in which electrodes implanted inside brain tissue deliver controlled pulses of electrical stimulation, are already used to relieve severe tremors in people with Parkinson’s disease whose symptoms can’t be controlled with medication.
Electrical activation of the nervous system is also being tested experimentally to treat the symptoms of a number of other neurological conditions, including epilepsy, multiple sclerosis, spinal cord injuries, and dystonia, a disorder in which involuntary muscle contractions cause uncontrolled and often painful movement.
