When people have a stroke, time is everything. During these events, regions of the brain are starved of oxygen, and the cells consequently begin to die. The longer it takes to get treatment, the more extensive the brain damage. But scientists have also discovered that there is a window directly after a stroke when people are able to relearn skills that might have been lost as a result of the condition. In addition, scientists have found that with mice they are able to “reopen” this window, by giving them a second stroke in the same region as the first. The results, however, cannot be applied to humans due to obvious ethical reasons.
To start with, mice were trained to complete a task that involved reaching through a small gap in their cage to grasp a piece of food. This behavior was very unnatural for the mice, but after spending 10 days in training, the rodents were able to successfully reach the food around half the time they tried. The researchers then induced a stroke within the motor cortex of the brain – the region responsible for voluntary movement – which prevented the rodents from being able to perform the task at all. After waiting a week, past the period of time during which scientists think the brain can recover following a stroke, the scientists tried to reteach the mice how to perform the task.
They found that the success rate for the rodents had fallen, with the mice now only successfully grasping the food around 30 percent of the time. The scientists then wanted to test whether this window of recovery could be reopened, and decided to do so by inducing a second stroke in the mice. For half the animals, they caused the stroke to occur again in the motor cortex, but for a control group they induced it in the visual cortex, far away from the site of the original stroke. Immediately following this, the researchers then taught the mice how to perform the task again.
For the mice that were given the second stroke in the motor cortex, the researchers found that the rodents were able to perform the grasping task as well as they could originally, regaining their 50 percent success rate. But for those that were given the stroke in the visual cortex, the mice never improved in their ability to complete the task. The study is published in the journal Neurorehabilitation & Neural Repair.
This, the researchers claim, suggests that the motor cortex is the only part of the brain that can be reopened in order to regain motor skills following a stroke, although exactly why this is remains unclear. While inducing the mice to have a second stroke appeared to achieve this, allowing them to be retaught previous skills, the scientists are aware that this technique would never be allowed on humans. What it does show, however, is that there is a lot more plasticity within the mammalian brain, and that it could lead to other ways to either reopen this window of recovery in humans or extend it to allow for greater time for recovery.
“If we can better understand how to reopen or extend the optimal recovery period after a stroke, then we might indeed change how we treat patients for the better,” Steven Zeiler, assistant professor of neurology at the Johns Hopkins University School of Medicine, said in a statement. “Our study adds new strong and convincing evidence that there is a sensitive period following stroke where it’s easiest to relearn motor movements – a topic that is still debated among stroke researchers.”