Effect of vagal nerve stimulation on auditory and visual event-related potentials

Chronic unilateral vagal nerve stimulation (VNS) has been recently introduc ed into the therapy for intractable epileptic seizures. Its effect on cogni tive functions in VNS-treated patients remains controversial. The aim of th e present study was to evaluate the possible impact of therapeutic VNS on c ognitive functions by means of event-related potentials analysis. Ten patie nts with medically intractable epilepsy, who had been implanted with VNS de vices, participated in the study. Auditory and visual event-related potenti als (ERPs) were repeatedly recorded, first just before the implantation of VNS devices, and then again 3-6 months after the device activation. The eff ect of lower intensity stimulation on the P3 component of ERPs was assessed . No significant differences were found in auditory ER-Ps; the latencies of P3 as well as N2/P3 peak-to-peak amplitudes were virtually identical. The same was true for mean P3 latencies of visual ERPs. However, higher visual N2/P3 peak-to-peak amplitudes were observed in the responses to targets tha t followed VNS, with a significant finding at the electrodes investigated. When comparing the effect of VNS on visual N2/P3 amplitude in each electrod e separately, the most expressive differences were found in the frontal reg ion. This observation supports the theory of a possible positive effect of low-intensity VNS on the cognitive functions.