Abstracts

RATIONALE: Electrical stimulation that is applied for cortical mapping may produce an afterdischarge (AD). A second electrical stimulus or cold Ringer's lactate may stop the AD by desynchronizing the discharge. Little is known about the intensity or duration of the stimulus needed to disrupt an AD. Moreover, it is not known whether an AD that occurs in the epileptogenic zone would respond differently than one that occurs outside this area. We examined this in a small group of patients. METHODS: Nine patients with partial seizures were prospectively studied between 3/1/99 and 3/1/2000. The epileptogenic zone was identified using continuous video-EEG monitoring and a combination of subdural and depth electrodes. If an AD was induced during cortical mapping, a second electrical stimulus was applied through the same electrode pair. If the second stimulus failed to stop the AD, additional stimuli were applied to a maximum of four. The intensity of the subsequent stimuli was equal to or greater than the stimulus that caused the AD. Successful termination of the afterdischarge was determined by visual inspection of the EEG. The duration, intensity, and time to initiation of the second stimulus were not controlled. RESULTS: 106 electrical stimuli were applied. 36% (4/11) of the ADs in the epileptogenic zone were terminated. 49% (47/95) of the ADs outside the epileptogenic zone were disrupted. The intensity of the second stimulus was between 2 mA and 14 mA. The duration of the stimuli ranged from 0.5 to 3 seconds. The time from onset of ADs to application of the second stimulus was 2 to 50 seconds. There was no significant difference in intensity, duration, or time to second stimulus between the two groups. CONCLUSIONS: Electrographic hypersynchronous epileptiform discharges can be stopped by the application of electrical stimulation in both epileptogenic and nonepileptogenic cortex. 48% of ADs were terminated with the application of an electrical stimulus in this study. However, for a therapy to emerge based on responsive electrical stimulation, the stimulation parameters must be refined.