Evoked potential studies in petit mal epilepsy. Visual information processing in relation to spike and wave discharges.

The evoked potential has been useful in studying characteristics of the epileptic nervous system. To investigate whether an alteration in sensory processing is possibly related to behavioral unresponsiveness observed to precede spike and wave bursts, average visual evoked potentials (VEPs) were studied during a 4.0 sec preburst interval in 6 patients with petit mal epilepsy. Individual responses, evoked by photic flashes, were averaged as a function of flash-to-burst interval. In 3 subjects with classical bursts of spike and wave, the average VEP was degraded 0.5 sec or less before burst onset. In 3 subjects with atypical electroencephalographic seizure discharge, VEP degradation was not seen. Some possible interpretations concerning the significance of the VEP alterations were discussed.