Neuromagnetic source localization of epileptiform activity in patients with graphogenic epilepsy

To clarify the source localization of epileptiform activity by using magnetoencephalography (MEG) in patients with graphogenic epilepsy.

MEG and simultaneous EEG were recorded with a 204-channel whole-head MEG system in two patients with graphogenic epilepsy. During the MEG recordings, the patients performed a set of tasks comprising mental arithmetic calculation, speaking, moving the right arm in a manner resembling writing, writing, and thinking of writing. Equivalent current dipoles (ECD) were calculated for epileptiform discharges on MEG by using a single-dipole model. The ECD were superimposed on the magnetic resonance images of the patients.

The task of writing provoked seizures, in which both patients jerked the right arms. Thinking of writing also induced these seizures. In both patients, EEG associated with the seizures showed bursts of spike-and-slow-wave complexes predominantly in the centroparietal region. MEG also showed epileptiform discharges corresponding to the EEG bursts. ECDs obtained from the discharges were clustered in the left centroparietal area.

Thinking of writing was a trigger for the seizures, as well as the task of writing. The source of the epileptiform discharge associated with the seizures was localized in the unilateral centroparietal area. The findings suggest that the centroparietal region plays an important role in the pathophysiology underlying these two graphogenic epilepsy cases.