Localization-related epilepsy exhibits significant connectivity away from the seizure-onset area.

In localization-related epilepsy, seizures are presumed to arise from a discrete cortical area. The control of seizures by epilepsy surgery can be poor, however, even when there has been complete resection of the area identified by standard clinical procedures to give rise to seizures. We used a coherence-based measure of functional connectivity to test for network effects within and outside the seizure-onset area. Connectivity was evaluated from the background intracranial electroencephalogram of six unselected patients. We show significant nonzero connectivity not only for the seizure-onset area but also several centimeters from it, for example, for the beta-frequency band (P<10(-5)), suggesting a nonlocal character to this disorder.