Occipital spikes and their relation to visual evoked responses in epilepsy, with particular reference to photosensitive epilepsy

Abstract

The responses to intermittent photic stimulation (IPS) at rates of 1–10 fl/sec were studied in seventy-two subjects, eighteen being normal controls, thirty-eight having photosensitive epilepsy and sixteen having epilepsy which was not clinically photosensitive. All patients showed abnormal responses to IPS. In most of the patients photic stimulation evoked negative occipital spikes with or without photoconvulsive responses. Comparison was made between the occipital spikes and the VERs in the same patient. This showed that there was no simple time relation between occipital spikes and components of the VERs. The VERs of the normal subjects showed no component with a latency corresponding to that of the negative occipital spikes seen in the patients. It is suggested that the non-specific thalamo-cortical system may be responsible for the genesis of the “epileptogenic” occipital spikes and that increased sensitivity of the occipital cortex is present in most photosensitive patients.