Occipital brain magnetic field (MEG) oscillatory responses were evoked upon static grating pattern subthreshold stimuli in 12 patients with photosensitive epilepsy and 2 matched control groups, one with epilepsy but no photosensitivity and the other healthy controls. The continuous wavelet transform (CWT) was employed to characterize the time–frequency energy dynamics and phase-locking of the early evoked gamma-band oscillatory responses (eGBR).
The photosensitive epilepsy group showed statistically significantly increased phase-locking of the gamma-band responses (eGBR) of the striate visual cortex in the (40–70 Hz) × (25–300 ms) and in the (25–30 Hz) × (300–600 ms) time–frequency windows with respect to the healthy controls.
Photosensitive epilepsy seems to be characterized by altered phase synchronization dynamics at a higher frequency range (a-frequency band) compared to healthy controls. Our results indicate that photosensitive epilepsy is driven by the large-scale phase-locking of the underlying striatal visual cortical unit oscillators in specific “photosensitive” frequency components (dynamic phase-attractor theory of epilepsy). Our method could provide a novel diagnostic tool in safely detecting, investigating and assessing response to treatment in photosensitive epilepsy.