Imaging provides clues to epilepsy

17 Jun 2002

Optical imaging that maps brain activity during a fit promises to help surgeons treat epilepsy.

Real-time imaging

Researchers at Germany's Max-Planck Institute for Neurobiology have developed an imaging technique that measures real-time changes in neuron activity during a neocortical epileptic fit (Nature Medicine 7 9).

Aimed at helping researchers to understand what triggers epilepsy and its spread through the brain, the technique monitors variations in light absorption of animal neural tissue.

Neocortal epilepsy is characterized by so-called ictal and interictal events that take place in the neocortex, the brain's largest external surface layer. Ictal events involve a rapid firing of neurons that leads to physical seizures, but smaller interictal activities often continue unnoticed.

To surgically treat a patient with neocortical epilepsy, doctors have to remove both activity zones. Ted Schwartz and Tobias Bonhoeffer's new method tracks both activity zones and could help doctors locate and remove these regions.

The researchers first illuminated the brain with a halogen lamp filtered to 707 nm wavelengths through two fiber-optic light guides. They focused a CCD camera and lens at just 500 microns beneath the cortical surface and then stimulated the brain to create epileptic activity.

By recording optical signals that were linked to changes in tissue absorption while grabbing images of the brain, Schwartz and Bonhoeffer built up high-resolution activity maps of ictal and interictal events.

"The key was figuring out how to set up the experiment and do the image division to capture epileptic activity," said Schwartz. "By subtracting images [taken before and after epilepsy events] we can uncover what is different between the two events."

Schwartz says the researchers are currently building a human imaging system. "We hope to begin using the technique within the next few months," he added.