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Rodents can recover from strokes that damage the primary motor cortex, the region of the brain that controls most movement in the body. Rewiring enables a different part of the brain to take over the lost function.

“Despite all of our approved therapies, stroke patients still have a high likelihood of ending up with deficits,” says study leader Steven R. Zeiler, assistant professor of neurology at the Johns Hopkins University School of Medicine. “This research allows us the opportunity to test meaningful training and pharmacological ways to encourage recovery of function and should impact the care of patients.”

More patients are surviving strokes because of improved emergency care. Still, as many as 60 percent are left with diminished use of an arm or leg; one-third need placement in a long-term care facility. The economic cost of disability translates to more than $30 billion in annual care.

“In people left with deficits after a stroke, we have been asking how we can encourage the rest of the nervous system to adapt to allow true recovery,” Zeiler says. “This research begins to provide us some answers.”

For the study, published online in the journal Stroke, researchers first trained normal but hungry mice to reach for and grab pellets of food in a precise way that avoided spilling the pellets; they received the pellets as a reward. The task was difficult to master, the researchers say, but the mice reached maximum accuracy after seven to nine training days.

Then the researchers created experimental small strokes that left the mice with damage to the primary motor cortex. Predictably, the reaching and grasping precision disappeared, but a week of retraining, begun just 48 hours after the stroke, led the mice to again successfully perform the task with a precision comparable to that they achieved before the stroke.

Subsequent brain studies showed that although many nerve cells in the primary motor cortex were permanently damaged by the stroke, a different area called the medial premotor cortex adapted to control reaching and grasping. Normal function of the medial premotor cortex is not well-understood, but in this case it seemed to take over the reach-and-grab task in the  experimental mice.

The researchers also report that otherwise healthy mice trained to reach and grasp pellets did not lose this ability after experiencing a stroke in the medial premotor cortex. That suggests that it usually plays no role in such activities and that its ability to take over the task might help human stroke victims.

The team’s next steps with their mouse model include evaluating the effect of drugs and timing of physical rehab on long-term recovery. The research could offer insight into whether humans should receive earlier and more aggressive rehab.

The Johns Hopkins University Department of Neurology, the National Institute of Neurological Disorders and Stroke, and the National Institute of Mental Health supported the study.

Source: Johns Hopkins University