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Lack of cortical contrast gain control in human photosensitive epilepsy


Television and video games may be powerful triggers for visually induced epileptic seizures. To better understand the triggering elements of visual stimuli and cortical mechanisms of hyperexcitability, we examined eleven patients with idiopathic photosensitive epilepsy by recording visually evoked potentials (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 (equiluminant red–green) stimuli. We conclude that cortical mechanisms of contrast gain control for pattern stimuli of relatively low temporal frequency and high luminance contrast are lacking or severely impaired in photosensitive subjects.

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The authors would like to thank M. C. Morrone for suggestions and discussion and C. Orsini for technical help.

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Correspondence to Vittorio Porciatti.

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Figure 1: Luminance-contrast gratings: effect of temporal frequency.
Figure 2: Luminance-contrast gratings: effect of contrast.
Figure 3: Luminance-contrast gratings of 4–10 Hz temporal frequency: effect of contrast in individual subjects.
Figure 4: Chromatic-contrast gratings: effect of temporal frequency and contrast.