Transition to seizure in photosensitive epilepsy.

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.

Regulations: what next?

Television (TV) is the most provocative visual stimulus and evokes (first) seizures in susceptible children and adolescents, especially when flickering and patterned images are shown. This has led to the initiative to develop guidelines for broadcasters. The development of new types of TV screens will not remove the need for control of broadcast material. It could be argued that rather than protect the whole viewing audience by application of broadcasting guidelines, only those who are photosensitive should be protected. But maybe we should do both, because most known sensitive patients will benefit from greater safety and will not be dependent on fashionable ideas by commercial broadcasters that are not (yet) familiar with the guidelines. No such guidelines exist for video material, electronic screen games, and the Internet. It would be wise to adopt the guidelines for video material and electronic screen games.