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Flipping on the Lights to Halt Seizures

Targeted light transmission to genetically altered brain cells stops seizures cold.

Strobe lights can trigger epileptic seizures. Now imagine a light that stops a seizure a split second after it starts. 

By applying pulses of light to genetically altered nerve cells deep in rat brains, researchers at Stanford and Pierre and Marie Curie University in France have done just that. Their results, which showed for the first time how a part of the brain called the thalamus is involved with epileptic seizures, were published today in Nature Neuroscience.

The study could point toward new targets for epilepsy treatment, says Ed Boyden, associate professor and leader of the Synthetic Biology Group at MIT. Boyden was not involved in the work. Some ideas “might emerge immediately from knowing new targets to insert deep brain stimulation electrodes,” a type of device already used to help people with epilepsy, Boyden says.

The latest research looked at a kind of seizure that sometimes follows damage to the cerebral cortex, the outer part of the brain, from strokes or head injuries. Previous reports had hinted that the cortex might also communicate during a seizure with the thalamus, the brain’s message relay center.

In the current study, experiments with rats confirmed that the thalamus propagates seizure activity originating in the cortex. To see if the thalamus could be a target for treating seizures, Jeanne Paz, the paper’s lead author, and her colleagues turned to optogenetics, a technology that lets researchers use light to turn brain cells on and off.

For the “genetics” part, they used a virus to insert the DNA code for a light-sensitive protein into thalamus cells of rats. When exposed to light, the protein interferes with these cells’ ability to communicate.

The researchers then developed a light source that would turn on only when a rat had a seizure. To detect seizures, they implanted electrodes into the rats’ brains. When these electrodes registered a seizure starting, light from a laser was aimed directly at the genetically altered thalamus cells. The result, the researchers found, was that flipping on the light immediately stopped the seizure activity, proving that the thalamus is needed to keep seizures going.

“We’re excited that just a brief light exposure was enough to stop the seizure,” says John Huguenard, Stanford professor of neurology and neurological sciences and an author of the study.

However, Huguenard says, an optogenetics-based brain implant to control seizures is a long way off because of the unknown risks of altering a person’s DNA with a virus. “I would want to be cautious,” he says.

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