Photic sensitivity of children with absence seizures in slow wave sleep.

Consequent upon previous studies on the effect of sleep on spike-wave discharges in absence seizures, photically sensitive spike-wave paroxysms were studied in 4 children with absence seizures, including identical twins, during various sleep stages. Sensitivity to stimuli at all frequencies and intensities was minimal during slow-wave sleep (stages 3 and 4), although photic driving could still be discerned. Trains of paired stimuli were effective in triggering polyspike responses during slow-wave sleep at frequencies of 6-8 c/sec and at flash intervals of 50 msec. The morphology of the discharges was similar to that seen in spontaneous discharges in deep sleep. The discharges, however, were stimulus-bound and there were no poststimulation spike-wave afterdischarges, which characterized wakefulness and REM sleep. The findings imply that, in deep sleep, while the cortical response to photic stimulation via the specific pathway system remains intact, the cortex appears to be functionally disconnected from those subcortical mechanisms essential for afterdischarge perpetuation.