Abstracts

Rationale: A long-term electroencephalographic(EEG) change caused by vagus nerve stimulation (VNS) as decreasing paroximal waves on EEG has been known, whereas an acute change has not been established so far. However, the high frequency component of EEG has not been considered because of scalp-recorded EEG is unable to detect it. We examined the effect of VNS on electrocorticography(ECoG) in a patient who had been receiving VNS. Methods: An 11-year-old boy with multifocal intractable epilepsy had VNS therapy for one year. He experienced some reduction of seizure frequency and severity but drop attacks newly appeared. Thus, total callosotomy was performed. During the surgery, cortical electrodes were placed on the bilateral superior frontal gyri and ECoG was recorded with a sampling rate of 2000 Hz. VNS stimulation signal was simultaneously recorded from a cervical skin electrode. Time frequency analysis was performed using EMSE software (Source Signal Imaging Inc. San Diego). We compared VNS-on and VNS-off phases and examined spatiotemporal dynamics of ECoG power in each bands. Results: Significant increase of power in 250-1000Hz was observed during VNS-on phase starting several seconds after the start of VNS. This reaction could not be attributed to an artifact of stimulation because the change stopped several seconds after the end of VNS. Conclusions: An acute VNS-induced ECoG change was demonstrated in this single patient. The change was restricted in high frequency bands, and that may be the reason why previous scalp EEG studies failed to detect this change. This VNS-induced augmentation of fast-ripple oscillation may partly explain the inhibitory effect of VNS on the cerebral cortices, since the activity of this band has been suggested to be closely associated with inhibitory interneurons.