Vagus nerve stimulation has no effect on awake EEG rhythms in humans

Vagus nerve stimulation (VNS) has been shown to have an anticonvulsant effect in several animal models, and clinical trials in patients were recently started. Experimental data have suggested that VNS may act by modulating EEG rhythmic activity. We studied the acute effects of VNS on EEG background rhythms in patients undergoing treatment for poorly controlled partial seizures. Six patients had recordings of satisfactory quality for quantitative EEG analysis. A significant effect of VNS on EEG total power, median frequency, or power in any of the conventional frequency bands, could not be demonstrated. Intraindividual analysis did not show a significant effect of VNS on total power for any patient, including those with apparent clinical response. We conclude that VNS at the parameters in current clinical use does not alter awake EEG background rhythms. The mechanism mediating acute antiepileptic effect remains unknown.