Study finds altered brain connections in epilepsy patients

Patients with the most common form of focal epilepsy have widespread, abnormal connections in their brains that could provide clues toward diagnosis and treatment, according to a new study published online in the journal Radiology.

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

To learn more, researchers performed 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 consisted of 24 patients with left temporal lobe epilepsy who were slated for surgery to remove the site from where their seizures emanated. The researchers compared them with 24 healthy controls using an MRI protocol dedicated to finding white matter tracts with diffusion imaging at high resolution. The data was analyzed with a new technique that identifies and quantifies structural connections in the brain.

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

"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.

Epilepsy is a disorder of the central nervous system, specifically the brain. In simple terms, our nervous system is a communications network that controls every thought, emotion, impression, memory, and movement, essentially defining who we are. Nerves throughout the body function like telephone lines, enabling the brain to communicate with every part of the body via electrical signals. In epilepsy, the brain's electrical rhythms have a tendency to become imbalanced, resulting in recurrent seizures.

If you have seen a picture of the brain before, it probably looked like this one, which illustrates the outer surface of the upper brain. This outer surface contains numerous folds that increase the surface area and allow more cerebral cortex to be packed into the skull, giving us more "brain power."