As many as 60 percent of people who suffer from a stroke are left with some kind of physical disability, ranging from blindness in one eye to loss of function in one or more limbs. As many as a third of these patients are placed in long-term care facilities.
New research from Johns Hopkins University offers hope for people recovering from a stroke and may give stroke patients a better chance for a complete recovery.
“Despite all of our approved therapies, stroke patients still have a high likelihood of ending up with deficits,” study leader Steven R. Zeiler, M.D., Ph.D., an assistant professor of neurology at the Johns Hopkins University School of Medicine, said in a press release. “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.”
We have some clever mice and our brain’s plasticity to thank for the latest stroke breakthrough.
The Power of the Brain
Training mice is no easy task, no matter how many medical degrees you have.
For this study, researchers trained healthy, hungry mice to reach for and grab food pellets in a precise way so that they didn’t spill any. Even with food as a reward, the task was difficult for the mice to master, but with seven to nine days of training, the mice reached maximum accuracy.
Researchers then created small strokes in the mice, which left them with damage to the primary motor cortex, one the areas of the brain that helps control the body’s ability to move. Just as they suspected, the mice were then unable to perform the pellet-grasping task with precision.
Researchers began to retrain the mice just 48 hours after the stroke. After one week, the mice performed the task almost as precisely as they did before the stroke.
Upon studying their brains, researchers found that while the stroke caused permanent damage to many nerve cells in the primary motor cortex, a different part of the brain—the medial premotor cortex—adapted and took over control of reaching and grasping.
This surprised researchers because, while the function of the medial premotor cortex still has an air of mystery to it, a stroke in that same area in healthy mice had no effect on their motor control. These results have led scientists to believe that our brains are far more plastic, or adaptable, than previously thought.
Mice are the preferred research subjects for experiments in human brain function because humans and mice share 90 percent of the same genes in their brains.
Taking Off the Brain’s ‘Brakes’
Besides the effect that precise, intense, and early intervention can have on the brain after a stroke, Johns Hopkins researchers also learned more about how the brain can “rewire” itself to take on new functions.
After the mice underwent the experimental stroke, there was a decrease in the level of a specific protein in their brains. This protein, parvalbumin, is a marker for neurons whose primary function is to keep the brain's circuitry from overloading. Basically, they are the brain’s brakes, which keep it from speeding off a cliff.
With lower levels of parvalbumin in the medial premotor cortex—the area of the brain that took over post-stroke—the brain was allowed to reorganize itself to assume new functions. For the mice, that included the ability to reach and grasp the food pellets.
When a stroke was induced directly in the medial premotor cortex in the mice, they lost their new skills but could still be retrained.
The research team’s findings were published in the American Heart Association journal Stroke.
This study further demonstrates that humans are still learning about the mysteries of the brain, namely it’s ability to adapt in the face of damage.
The Johns Hopkins team plans to use the mouse experiments to evaluate the effect of drugs on stroke recovery and the importance and timing of physical rehabilitation for long-term improvement.
The goal is to discover whether humans who suffer a stroke should begin immediate and aggressive rehabilitation.
“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 said. “This research begins to provide us some answers.”