High-frequency changes during interictal spikes detected by time-frequency analysis

Objective: High-frequency (HF) changes were analysed in relation to anatomical origin of spikes, shape and occurrence within the seizure onset zone (SOZ). We evaluated whether HF changes are linked to the SOZ, as established for distinct high-frequency oscillations. Methods: SEEG was filtered at 500 Hz and sampled at 2000 Hz. Spikes were selected by shape (spike/spike-slow wave) and location (SOZ/non-SOZ and neocortex/amygdala/hippocampus) in 15 patients. About 50 spikes were averaged for each set. Changes compared to baseline were quantified with false discovery rate controlled t-statistics using time-frequency spectra. Counts of increased or decreased time-frequency values were compared across spike categories in the 80-250 and 250-500 Hz bands. Results: Seventy-seven spike types were analysed. Differences between spike categories were most prominent between 250 and 500 Hz. HF changes were more frequent and larger in mesial temporal than in neocortical spikes and for spikes with slow waves than spikes alone. HF changes above 250 Hz were more frequent in spikes within than outside the SOZ. Conclusions: HF increases above 250 Hz show regional differences and are very prominent in the SOZ. Hippocampal spikes have the strongest HF components. Significance: Analysis of HF changes during spikes may provide information on differing pathophysiological mechanisms of spikes and on epileptogenicity of the tissue. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.