Occipital spikes in photosensitive patients with generalized PPR

(Left) Patterned intermittent photic stimulation (2 mm × 2 mm graticule superimposed on the grass of the stroboscope) evoked occipital spikes, which are time-locked to flash at 6 flashes/second of a patient with spontaneous and photically elicited GTCS. Higher flash frequencies from 9 to 30 Hz elicited generalized photoparoxysmal response (PPR) of spike-wave, briefly preceded by occipital spikes. (Right) Emergence of occipital spikes from the P100 VER component with increasing flash rate. Patient had spontaneous and television-induced GTCS. On EEG, time-locked occipital spikes were apparent only at 5 flashes/second whereas higher flash rates from 6 to 26 Hz elicited generalized discharges of spike-wave briefly preceded by occipital spikes. The three upper traces show the average visual-evoked response (VER) to stimulation at 2, 3.5, and 4 flashes/second. The occipital spikes evoked at 7 and 8 flashes/second are shown in the 2 lower traces. The vertical line crosses the negative component of the occipital spikes and the Vb component of the P100 component of the VER. The horizontal line indicates time in milliseconds. The thick arrow indicates the onset of flash. (Modified with permission from: Panayiotopoulos CP, Jeavons PM, Harding GF. Relation of occipital spikes evoked by intermittent photic stimulation to visual evoked responses in photosensitive epilepsy. Nature 1970;228:566-7.)