Anterior-posterior relationships of EEG in photosensitive subjects: coherence and cross-phase-spectral analysis.

Coherence and cross-phase-spectral analysis of EEG were applied to photo-sensitive subjects to investigate the mechanism of the generalization of photo-induced paroxysms. Coherence values were high between frontal (F) and central (C) in resting records and between F-C in EEGs revealing harmonic responses, where the coherence values of F-O (occipital) were also high, and the waves of F preceded those of O. In cases of occipital-localized 3/6 Hz (poly) spike-waves, discharges of O preceded those of F. During the stage of generalized paroxysms, discharges were highly cohered between all electrodes. Discharges of F preceded those of O, and appeared to play as a generator. Two conditions with clinical symptoms had higher frequencies (greater than or equal to 12 Hz) and shorter time lags (less than or equal to 5 msec) than conditions without symptoms.