Generalized paroxysmal discharges induced by visual stimuli and eye movements

The generalized paroxysmal discharges (GPDs) induced by the visuo-sensory and oculomotor activations in a total of 30 patients were investigated. The patients consisted of 27 epileptics and 3 with sequelae of head trauma; all of them showed photoconvulsive response. The visuo-sensory activation with red-flicker of 15 cycles/sec or with visual stimuli containing patterns, "pattern," was carried out under the constant condition of 20 cd/m-2. In 22 cases (73%), G-type (simultaneous occurrence of GPD over all the areas) was induced by red-flicker, while in 28 cases (93%) P-type (GPD was preceded by posterior spikes) was induced by "pattern." With the oculomotor activation, paroxysmal discharges were induced in 11 cases of photogenic epilepsy; 10 cases (91%) were of A-type (GPD was preceded by anterior spikes), and one case (9%) showed focal spikes over the right frontal area. In 21 cases (70%), the type of GPD changed from G-type to P-type as the red-flicker activation was replaced by the "pattern" activation. Further, in seven (33%) out of the 21 cases it changed from P-type to A-type as the activation with "pattern" was replaced by the oculomotor activation. It was suggested that the non-specific thalamo-cortical system, the visual cortex, and the frontal eye field are chiefly concerned with the occurrences of G-type, P-type, and A-type, respectively, when such stimuli as described above are given independently.