Study Discovers Altered Brain Connections in Epilepsy Patients

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Based on a new study published online in the journal Radiology, patients with the most prevalent form of focal epilepsy have widespread, abnormal connections in their brains that could offer clues toward diagnosis and treatment.

Temporal lobe epilepsy is defined by seizures stemming from the temporal lobes, which are situated on each side of the brain just above the ear. Previously, experts believed that the condition was associated to isolated injuries of structures within the temporal lobe, like the hippocampus. However, recent research has connected the default mode network (DMN), the set of brain regions activated during task-free introspection and deactivated during goal-directed behavior. The DMN is comprised of several hubs that are more active during the resting state.

To learn more, researchers conducted diffusion tensor imaging, a type of MRI that tracks the movement, or diffusion, of water in the brain's white matter, the nerve fibers that transmit signals throughout the brain.

The study group was made up of 24 patients with left temporal lobe epilepsy who were scheduled for surgery to remove the site from where their seizures originated. The researchers compared them with 24 healthy controls using an MRI protocol programmed to finding white matter tracts with diffusion imaging at high resolution. The data was then analyzed with a new technique that identifies and quantifies structural connections in the brain.

Patients with left temporal lobe epilepsy showed a decrease in long-range connectivity of 22 percent to 45 percent among areas of the DMN when compared with the healthy controls.studyfind brain

"Using diffusion MRI, we found alterations in the structural connectivity beyond the medial temporal lobe, especially in the default mode network," said Steven M. Stufflebeam, M.D., from the Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital in Boston.

In addition to reduced long-range connectivity, the epileptic patients had an 85 percent to 270 percent increase in local connectivity within and beyond the DMN. The researchers believe this may be an adaptation to the loss of the long-range connections.

"The increase in local connections could represent a maladaptive mechanism by which overall neural connectivity is maintained despite the loss of connections through important hub areas," said Stufflebeam.

The results are supported by previous functional MRI studies that have pointed to a decreased functional connectivity in DMN areas in temporal lobe epilepsy. Researchers are not sure if the structural changes cause the functional changes, or vice versa.

"It's probably a breakdown of myelin, which is the insulation of neurons, causing a slowdown in the propagation of information, but we don't know for sure,"said Sufflebeam.

As of now, Stufflebeam and colleagues plan to delve deeper into their research, utilizing structural and functional MRI with electroencephalography and magnetoencephalography to track diffusion changes and look at real-time brain activity.

"Our long-term goal is to see if we can we predict from diffusion studies who will respond to surgery and who will not," he said.

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