EEG synchronization changes during low-frequency electric stimulation of the seizure onset zone

Purpose: To assess whether EEG sychronization changes during short-term low-frequency electrical stimulation of the seizure onset zone.

Methods: In 10 patients (34±11y) with pharmaco-resistant epilepsy the seizure onset zone (9 temporal lobe, 1 frontal lobe) was electrically stimulated by intracranial electrodes at 1Hz for 5min. Bipolar stimuli were applied and 4 different pulse widths (0.05,0.1,0.5 an 1.0ms) were tested. Stimulation amplitudes were held fixed at 1mA for strip electrodes and at 2mA for depth electrodes. Changes of EEG synchronization were assessed by the eigenvalue dynamics of the cross-correlation matrix computed from a 2.5s sliding window.

Results: 37 stimulations were performed. EEG desynchronization occurred in 49% (18/37), an increase of EEG synchronization in 27% (10/37) and an EEG pattern with no significant change of synchronization in 24% (9/37). EEG synchronization most frequently occurred when stimulating with a pulse width of 0.5ms. A single patient had bilateral independent seizure onsets and stimulation effects on EEG synchronization were different for each side. In the patient with the shortest duration of temporal lobe epilepsy, stimulation triggered periodic epileptic spikes phase-locked to stimulation. One patient experienced an aura during stimulation, which did not evolve into a seizure and in one patient a subclincial seizure occurred.

Discussion: Low-frequency stimulation of the seizure onset zone is associated with different changes of EEG synchronization and its effects depend on the widths of the stimulation pulses. It may be an appropriate stimulation technique for long-term studies assessing whether synchronized or desynchronized brain dynamics prevent seizure occurrence.