Cortical location of benign paroxysmal rhythms in the electrocorticogram

Background: Six/second spike waves, 14 and 6/second positive spikes and small sharp spikes are apiculate paroxysmal rhythms in the electroencephalogram, thought to be of no diagnostic importance. The cortical origin of these discharges is documented in this report. Methods: These waveforms were assessed in recordings from the surface of the cerebral cortex using implanted subdural electrodes in 61 patients monitored for possible epilepsy surgery. Results: Eight patients had 6/second spike wave, four had 14 and 6/second positive spikes and 3 had small sharp spikes. The 6/second spike waves were localised to the posterior cingulate gyrus, a more restricted region than would be predicted from scalp recordings and the 14 and 6/second spikes to the posterior mesial temporal cortex. Small sharp spikes were more widely distributed but also predominated in the posterior mesial temporal area. None of the discharges were congruent with the focus of seizure origin and no interaction with other interictal spikes was found. Conclusion: These benign paroxysmal rhythms can appear incidentally in the electrocorticograms of patients with focal epilepsy and should not be confused will] focal pathological spike activity or considered to be of any value in localizing the seizure focus.