Lack of cortical contrast gain control in human photosensitive epilepsy

Television and video games may be powerful triggers for visually induced ep ileptic seizures. To better understand the triggering elements of visual st imuli and cortical mechanisms of hyperexcitability, we examined eleven pati ents with idiopathic photosensitive epilepsy by recording visually evoked p otentials (VEPs) in response to temporally modulated patterns of different contrast. For stimuli of low-medium, but not high, temporal frequency, the contrast dependence of VEP amplitude and latency is remarkably abnormal for luminance contrast (black-white), but not so for chromatic contrast (equil uminant red-green) stimuli. We conclude that cortical mechanisms of contras t gain control for pattern stimuli of relatively low temporal frequency and high luminance contrast are lacking or severely impaired in photosensitive subjects.