Epilepsy may not be the first side effect to come to mind when you think about the after-effects of a stroke. But epileptic seizures are a relatively common result of a stroke; some studies estimate that more than 10% of stroke victims develop seizures afterward.
Despite the prevalence of epilepsy among stroke sufferers, researchers have had little idea why the two are connected. Because strokes often involve the injury or death of a region of the cortex -- the outer shell of the brain -- scientists had postulated that the function of the areas around the brain might be disrupted by the injury, leading to seizures.
Now a new study suggests that theory might well be wrong, or at least incomplete. In a report published Wednesday in the journal Nature Neuroscience, scientists used a mouse model of stroke to show that the epileptic seizures were being controlled at least in part by areas deep within the middle of the brain -- in particular, an area called the thalamus, which acts as a sort of central processing center in the brain.
The thalamus has been implicated in seizures not caused by stroke, and it’s directly connected to the cortex, where the seizures are generally detected, helping to control the activity there. Since seizures are caused by an overwhelming amount of electrical activity generated by brain cells, they thought that turning down the activity in the thalamus might help.
First, the team studied cells from the thalamus after a stroke and found that they did indeed appear to seize, suggesting the area plays a role in epilepsy. The researchers then confirmed in living mice that giving them strokes did indeed cause epilepsy; while none of the seven control animals had a seizure during the study, three of the five mice that underwent a stroke did.
Could the seizures be stopped by shutting down the thalamus? To address this question, the team turned to a hot technique called optogenetics -- the use of light to turn specific cells on and off. Researchers added a protein to brain cells in the thalamus that prevented the cells from becoming active when they are flashed with a yellow light implanted near the thalamus. If their hypothesis was correct, flashing the yellow light should stop a seizure in progress. That’s exactly what they found.
But they didn’t stop there. They went on to build what’s called a closed-loop system that is able to detect seizures and flash the yellow light all on its own when a mouse begins to seize. And it worked: Once the system was installed, it stopped seizures all on its own.
Such a system is a tantalizing possibility for the treatment of humans with seizures, but an advance like that remains a long way off. The optogenetic technique would require gene therapy to get the light-sensitive protein into the thalamus, and it remains unclear what side effects turning those cells off might have.
Still, the findings bring researchers one step closer to understanding what causes epileptic seizures, and raises hope we might one day be able to turn seizures off without raising a finger.
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