Hemifield red flicker stimulation in a patient with pattern-sensitive epilepsy.

The provocative effects of paroxysmal discharges (PDs) by lateral, upper, and lower hemifield red flicker stimuli were studied in a 24-year-old female patient with pattern-sensitive epilepsy, who showed a generalized photoconvulsive response. In this patient fullfield red flicker stimulation provoked generalized PDs, whereas hemifield red flicker stimuli showed the following characteristics. (a) Left hemifield red flicker stimulation provoked focal PDs in the right posterior regions. (b) Right hemifield red flicker stimulation, on the contrary, was apparently less effective than the left in provoking focal posterior PDs in the contralateral hemisphere. (c) Lower hemifield red flicker stimulation provoked focal posterior PDs that were slightly more pronounced over the right side. (d) No definite PDs were provoked by upper hemifield red flicker stimulation. These results were considered to be suggestive of the following conclusions. (a) Red flicker from the left lower quadrant of the visual field may be the most potent stimulus in provoking focal posterior PDs. (b) The right occipital lobe may be more sensitive to red flicker stimulation than the left occipital lobe. (c) In consideration of the retinotopic projection from the left lower quadrant of the visual field onto the visual cortex, the right upper lip of the visual cortex is presumed to be the most sensitive to red flicker stimulation. It is suggested that hemifield red flicker stimuli might be useful for EEG examination of the visual cortex in patients with photosensitive epilepsy, who are particularly sensitive to red flicker stimulation.