MENTAL-IMAGERY OF PHOTIC-STIMULATION PROVOKES PAROXYSMAL EEG ACTIVITYIN A PHOTOSENSITIVE PATIENT WHO SELF-INDUCES SEIZURES

This article reports a case of a 14 year-old male photosensitive epile ptic patient who was able to induce fits subjectively by the mental im agery of the effective visual stimuli. The patient underwent a compreh ensive electroencephalographic (EEG) examination including hyperventil ation. The basic EEG showed abnormalities. intermittent photic (IFS) a nd pattern stimulations (PtnS), evoked photo and pattern paroxysmal re sponses (PPRs) within a wide range of frequencies from 2-50 flashes pe r second (fps) and 0.5-6 cycles per degree (cdp) respectively. The pat ient was able to reconstruct the PPRs mentally on exposure to the effe ctive stimuli of 25 and 50 fps, and 2.0 and 3.25 cpd respectively. His cognitive functions were not affected when exposed to photostimulatio n. However, on exposure to pattern stimulation, he became totally conf used and his consciousness was impaired. These findings showed that se lf-induction of fits in photosensitive epilepsy is a mental phenomenon which takes place with or without loss of cognitive function dependin g on the rate and frequency of the physical and the 'imagined' stimuli .