Responsiveness at the onset of spike-wave bursts

A clear understanding of responsiveness during generalized spike-wave discharge has been the goal of many investigators. No previous studies have enabled a precise evaluation of a particular time point in the spike-wave bursts. A paroxysm-triggered method for measuring reaction time at specific time points during spike-wave discharge has been developed. The apparatus used was a modified reaction-time device consisting of an auditory stimulus, a response unit, and a digital clock. A threshold detector constantly monitored the EEG voltage; when a large amplitude spike-wave discharge occurred, a pulse was sent to a triggering device that turned on the stimulus unit and the clock, permitting testing of responsiveness at the exact onset of the paroxysm. Fourteen patients were tested in the Clinical Neurophysiology Laboratory of the University of Virginia Medical Center. A total of 286 stimuli during 235 spike-wave discharges were delivered. Of the 137 stimuli delivered simultaneously with paroxysm onset, 56% of the responses were abnormal (>2 S.D.) when compared to the normal reaction time for each patient at each session. In paroxysms of brief duration, more than 50% of the responses to stimuli delivered simultaneously with onset of the paroxysms were abnormal. Reaction times measured at varying intervals after the onset of the paroxysm were more frequently abnormal than at paroxysm onset; this could be considered evidence for a gradual decrease in responsiveness. Degree of spike-wave generalization, however, appeared to be inversely related to responsiveness. Further investigations will employ a variable delay after paroxysm onset; this method should further define the decrement in responsiveness during spike-wave bursts. Une compréhension claire de la réactivité au cours des décharges de pointe-ondes généralisées a été la préoccupation de nombre d'investigateurs, mais aucune étude antérieure n'a permis d'évaluation précise d'un moment particulier de ces bouffées de pointe-ondes. Les auteurs ont développé une méthode de mesure du temps de réaction, déclenché par les paroxysmes à des moments spécifiques au cours de la décharge de pointe-ondes. L'appareil utilisé est un système modifié d'étude du temps de réaction consistant en un stimulus auditif, une unité de réponse, et une horloge digitale. Un détecteur de seuil contrôle en permanence le voltage de l'EEG; quand une décharge de pointe-ondes de grande amplitude survient, une impulsion est envoyée à un système