Seizure discharges localized to the posterior cerebral regions in man, provoked by intermittent photic stimulation

Abstract

1.1. Electroencephalographic seizure discharge localized to the temporo-parieto-occipital region can be precipitated by intermittent photic stimulation alone, provided that the evoked potentials of large amplitude are induced under two conditions: 1.1.(a) when there is a pre-existing irritative lesion in the temporo-parieto-occipital region;1.2.(b) when photic stimulation provoked generalized spike-and-wave complexes.2.2. An electro-clinical correlation study has been carried out in 12 patients. The seizure discharge always preceded the onset of clinical signs. In some cases, a seizure was precipitated which differed from any of the patient's previous seizures. Some seizure discharges remained sub-clinical.3.3. The discharge consisted of rhythmic spikes occupying the temporo-parieto-occipital region of one or both hemispheres and these spikes might remain localized or irradiate forward. The discharges were often of long duration. They tended to facilitate the appearance of generalized spike-and-wave discharges in those cases in which the latter occurred spontaneously, or were provoked by photic stimulation.4.4. The authors believe that two factors play an important part in the precipitation of these seizure discharges: 4.1.(a) the arrival of specific afferents; this may permit one to consider these seizures as examples of “reflex epilepsy”;4.2.(b) the existence of cortical hyperexcitability, either diffuse or localized to this temporo-parieto-occipital region.