title: Excitability of evoked sharp wave: a case study.
abstract: In a 16-year-old boy, a sharp wave occurred spontaneously and was evoked by each individual light flash at rates of less than 4 f/sec. The excitability of the sharp wave was studied by use of double flashes at different intervals as well as IPS at different rates. With double flashes at intervals of 25 msec to 1 sec, the absolute refractory period was estimated to be less than 75 msec, and the subnormal excitability period in the range of 75 msec to less than 1 sec. With increased rates of flash trains from 3 to 24 f/sec, the sharp waves disappeared at the average rate of 10.4 f/sec. The disappearance of sharp waves at higher rates may be due to both the absolute refractoriness and the subnormal excitability. The sharp waves tended to vary in a waxing and waning manner. With long-lasting stimulation at a rate of 1 f/sec, sharp waves disappeared 30 sec after the stimulus onset. In our case, therefore, various factors influenced the excitability of the sharp wave response over a short to long period of time.
mesh_terms: D000293:Adolescent; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology*; D005074:Evoked Potentials, Visual; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D012032:Refractory Period, Electrophysiological; D013997:Time Factors