Images of the living brain, made while stroke victims and normal subjects tap their fingers, are revealing how some stroke patients regain lost strength. Such studies may suggest ways to foster similar recovery in those not as fortunate.
Dr. Steven C . Cramer worked on these studies during a fellowship with Dr. Seth Finklestein at Harvard University. Cramer will continue related research as a new assistant professor of neurology at the University of Washington.
“Our study patients ranged from two weeks to one year post-stroke. When they had their stroke was not important to this study. What mattered is these patients had good recovery, and we wanted to learn why,” Cramer explained.
The researchers used a viewing technique called functional m agnetic resonance imaging. FMRI not only gives a realistic picture of living brain anatomy, but also shows physiological changes when a person tries to move. Bright pools of color mark where neurons, or brain cells, are at work. At the start or stop of a movement, the colors turn on or off.
The researchers observed a few tricks some stroke victim’s brains call into play to compensate for injury. The first trick: some people, initially paralyzed in one arm, use both sides of the brain to move the rec overed hand. In contrast, normal subjects tapping the left fingers would activate a site on the right side of the brain, and vice versa.
What occurs in stroke patients with good recovery isn’t a new brain event. The same trick is seen when a normal subject performs a highly complex task.
Cramer explained, “Just to get out of bed in the morning, a stroke patient has to turn on all the areas of the brain a golfer would use to sink an 18-foot putt.”
Initial evidence shows some people have at least two controls for finger movement: one that governs the fingers on the opposite side of the body, and another that can, when necessary, move the fingers on the same side or both sides.
A second brain trick, demonstrated by about half the normal subjects and half the recovered stroke patients, is an increased ability to recruit areas richly connected to the motor cortex of the brain to supplement the main motor control area. Earlier researchers first discovered supplemental motor areas through br ain mapping — electronic probing to detect vital areas to protect during brain surgery. Supplemental motor areas now can be observed with functional magnetic resonance imaging. Their increased activity after stroke might represent alternate strategies to plan a movement, or could be reliance on undamaged pathways to carry messages out of the brain in parallel with pathways affected by the stroke.
Strokes vary in the amount of harm done. Sometimes the wreckage is small and deep but hits like a bomb d ropped on Grand Central Station during rush hour. Other times, the damage is larger, extending to the brain’s surface and boring a hole in the cortex.
People recovering well from major stroke show a third type of brain cell regrouping. Their functio nal MRI’s reveal active spots along the wound’s rim.
“It’s almost as though the brain relocated its motor headquarters to the nearest viable part of the cortex,” Cramer said. Reshuffling and reorganization within the brain is known as plasticity.
Another of Cramer’s studies brings in bedside analysis of hand strength after a stroke. A computer measures the patients’ grip on their good side and on the affected side. For more than a century physicians have noticed that stroke patients trying to move only the affected hand can’t keep the unaffected hand still, a phenomenon called mirror movements.
“Mirror movements may be telling us about enhancements the brain is making to increase motor output,” Cramer said.
Combining these windows o n the brain with studies of treatment during the early stages of stroke and soon after might uncover new protocols that improve the extent of recovery. Cramer, a neurologist, hopes to collaborate with rehabilitation specialists, basic neuroscientists and emergency medicine experts.
“Many people who survive a stroke remain disabled for the rest of their lives,” Cramer said. “Anything medical science can do to help these patients regain function could make a big difference in the quality of their years ahead.”
Cramer practices at University of Washington Medical Center and with the Veterans Affairs Puget Sound Health Care System.