title: Changes of EEG synchronization during low-frequency electric stimulation of the seizure onset zone.
abstract: OBJECTIVE
  To assess whether EEG synchronization changes during short-term low-frequency electrical stimulation of the seizure onset zone.
  
  
  METHODS
  In 10 patients (34+/-11 years) with pharmaco-resistant epilepsy the seizure onset zone (9 temporal lobe, 1 frontal lobe) was electrically stimulated at 1Hz for 5min via intracranial electrodes. Bipolar stimuli were applied and four pulse widths (0.05, 0.1, 0.5, and 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. We observed EEG desynchronization 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. In a patient with bilateral independent seizure onsets 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 sub-clincial seizure occurred.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Klinik für Epileptologie, University of Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany. kaspar.schindler@gmail.com
authors.forename: Kaspar
authors.initials: K
authors.lastname: Schindler
authors.forename: Christian E
authors.initials: CE
authors.lastname: Elger
authors.forename: Klaus
authors.initials: K
authors.lastname: Lehnertz
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000627:therapeutic use; D001921:Brain / Q000502:physiology; D003344:Cortical Synchronization; D004351:Drug Resistance; D004558:Electric Stimulation; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures; D012640:Seizures / Q000188:drug therapy / Q000503:physiopathology* / Q000601:surgery; D016896:Treatment Outcome
chemical_list: D000927:Anticonvulsants