Visual cognitive disturbance during spike-wave discharges
Cognitive functions of patients showing slow spike-wave discharge in EEG without obvious absence seizures were investigated using tachistoscopic stimuli triggered by spike-waves. Response times obtained during spike-waves and during non-spike-waves were compared for three tests (tapping, simple reaction, and morphological discrimination). We present one case of Lennox-Gastaut syndrome in which the test results could be statistically confirmed. The tapping test was interrupted by the occurrence of spike-waves. Response times during spike-waves were more delayed than during non-spike-waves in both the simple reaction tests and morphological discrimination tests. The differences in response times measured during spike-waves and during non-spike-waves were significantly greater in the morphological discrimination test than in the simple reaction test. The positive correlation between the length of spike-waves and response time in the discrimination test was significantly more pronounced than in the reaction test. These results were also confirmed in two other patients with Lennox-Gastaut syndrome. We conclude that spike-wave discharges may impair cognitive processing more intrinsically than motor functions.