A new study published online in the journal Radiology indicates that patients with left temporal lobe epilepsy have abnormal connections in their brains that could lead to clues toward diagnosis and treatment. According to one of the researchers, Steven M. Stufflebeam, M.D., from the Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital, the research team’s long-term goal is to determine if they can predict from diffusion studies who will and who will not benefit from surgery.
Temporal lobe epilepsy is characterized by seizures emanating from the temporal lobes. For some time, 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, Stufflebeam and team 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.
The findings: 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.
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 results are supported by prior functional MRI studies that have shown decreased functional connectivity in DMN areas in temporal lobe epilepsy. Researchers are not certain if the structural changes cause the functional changes, or vice versa.
The study is part of the Human Connectome Project, a five-year project funded by the National Institutes of Health that uses neuroimaging techniques to study connectomics, or the functional and structural connections in the brain. Dr. Stufflebeam’s colleague, Matthew N. DeSalvo, M.D., initiated the study as a medical student with the help of a 2013 Research Medical Student Grant from the Radiological Society of North America (RSNA).