Facilitatory effects of intermittent photic stimulation on visual cortical kindling

There are few reports on kindling preparation by daily electrical stimulation to the primary visual cortex. In our previous studies on cats, it was demonstrated that repeated stimulation to the primary visual cortex brought a similar progress in seizure development as in amygdaloid kindling, although it took more trials. In this study, we examined the effects of intermittent photic stimulation (IPS) (2.5 Hz) on the visual cortical kindling preparation to clarify more underlying mechanisms of photosensitivity. Under IPS, afterdischarges synchronizing to IPS were seen and a duration of afterdischarge was extremely prolonged, even in the early stage of the kindling process. The threshold of stimulus intensity inducing afterdischarge was significantly reduced and the generalized convulsive seizure was obtained with fewer times of stimulation, as compared to visual cortical kindling without IPS. In visual cortical kindling myoclonic responses were sometimes caused by IPS for a few minutes immediately after cessation of the electrically induced generalized seizure. Such phenomena were never seen in amygdaloid kindling. These results indicate that IPS facilitates a seizure development in all stages of visual cortical kindling.