Changes of visually evoked potential during seizure development in kindled cats.

The secondarily induced changes of brain function following seizure seen in kindling preparations were studied by means of the visually evoked potential (VEP) in unrestricted cats. The kindling was developed by repeated electrical stimulation to the visual cortex under intermittent photic stimulation (IPS). Generalized convulsion was rapidly developed with a lowering of threshold inducing afterdischarge and an earlier spreading of seizure discharge to the midbrain reticular formation as compared with the previous control experiment without IPS. Following electrical stimulation, a marked enhancement in amplitude and a prolongation in latency of the second negative component, which was not usually recognized before the electrical stimulation, was observed. Such augmentation of VEP developed progressively and finally changed into the epileptic discharge accompanied with myoclonic response. Furthermore, postictal augmentation of VEP which attained to maximum within a few minutes after the end of seizure was confirmed with an elevation of photosensitivity. It was noted that the second negative component continued significantly to exist for more than 60 min contrary to the relatively rapid restoration of the first negative component. These findings are discussed in relation to the mechanism of kindling phenomenon.