title: Transition to seizure in photosensitive epilepsy.
abstract: Photosensitive epilepsy (PSE) offers a highly reproducible model to investigate whether changes in neuronal activity preceding the transition to an epileptic photoparoxysmal response (PPR) may be detected. We investigated this possibility in patients with idiopathic PSE using MEG, as well as normal controls and non-photosensitive epileptic patients of the same age group. Spectral analysis of the MEG signals recorded during intermittent light stimulation revealed relevant information in the phase spectrum. To quantify this effect, we introduced a second order response feature of the stimulus-triggered visual response preceding the PPR: the phase clustering index, which measures how close the phases of successive periods are grouped for each frequency component for all periods of the stimuli applied. We found that an enhancement of phase synchrony in the gamma-band (30-120Hz), harmonically related to the frequency of stimulation, preceded the stimulation trials that evolved into PPRs, and differed significantly from that encountered in trials not followed by PPR or in control subjects. Thus this index can be considered a valuable index of the pro-ictal transition to seizures in photosensitive epilepsy.
authors.affiliation: Center of Neurosciences, Swammerdam Institute of Life Sciences, University of Amsterdam, Kamer C3-269, Science Park 904, 1098 XH Amsterdam, The Netherlands. F.H.LopesdaSilva@uva.nl
authors.forename: Fernando H
authors.initials: FH
authors.lastname: Lopes da Silva
authors.forename: Graham F A
authors.initials: GF
authors.lastname: Harding
mesh_terms: D001921:Brain / Q000503:physiopathology; D058256:Brain Waves; D004569:Electroencephalography; D020195:Epilepsy, Reflex / Q000150:complications*; D006801:Humans; D015225:Magnetoencephalography; D010775:Photic Stimulation / Q000009:adverse effects; D012640:Seizures / Q000209:etiology*; D012815:Signal Processing, Computer-Assisted