Chemosensory Function in Patients With Vagal Nerve Stimulators

Abstract

Chemosensory function is determined by the interplay of numerous sensory modalities. The present study aimed to evaluate the possible influence of electrical stimulation of the left-sided vagal nerve on gustatory and olfactory function in patients with vagal nerve stimulation (VNS). Gustation and olfaction were tested using psychophysical techniques; olfactory function was additionally evaluated using event-related potentials. A total of 11 subjects participated (six men and five women, aged 21 to 56 years). The vagal stimulator was run in "rapid cycle mode" in 10 patients, whereas one patient was treated with "normal mode" VNS. Subjects participated in two sessions, with the vagal stimulator switched on and off, respectively. The sequence of the two sessions was randomized across all participants. Using air-dilution, olfactometry event-related potentials to the specific olfactory stimulant H2S were recorded. Psychophysical tests were performed using the "Sniffin' Sticks" test kit, a test for retronasal olfactory function, and a gustatory test based on impregnated filter paper. The study yielded the following major results: (1) VNS produced a prolongation of P2 latencies of olfactory ERP, and (2) patients with therapeutic benefit from VNS in terms of seizure control had larger amplitudes during the on period than during the off period. In conclusion, using electrophysiological measures of olfactory function, the present study indicated a significant role of VNS in the processing of olfactory information.

Changes in Gustatory Perceptions of Patients with Major Depression Treated with Vagus Nerve Stimulation (VNS)

“…The present study revealed statistically signifi cant increases in the perception intensity of the fl avours " sweet " and " bitter " during stimulation with VNS in comparison with resting conditions with the VNS device switched off . Although Kirchner et al [25] found an infl uence of vagal nerve stimulation on olfactory information processing and a prolongation of P2 latencies of olfactory ERP in patients suff ering from epilepsies, the present study failed to show marked changes in olfactory perceptions during stimulation in patients suff ering from major depression. On the contrary, measurement of the perception of taste resulted in a decreased intensity threshold value in the study participants under stimulation conditions.…”

Improvement of Olfactory Function With High Frequency Non-invasive Auricular Electrostimulation in Healthy Humans

“…In a recent study, Frangos et al ( 2015 ) has demonstrated that non-invasive VNS of the auricular branch of the vagus nerve via the left cymba conchae of the external ear, produced similar effects to invasive VNS. This finding highlights the potential benefits of using non-invasive VNS, similar to the application of invasive VNS in previous studies (García-Díaz et al, 1984 ; Kirchner et al, 2004 ; Sperling et al, 2011 ). To explore the potential benefits of high frequency VNS, based on a previous study using invasive VNS in animal models (García-Díaz et al, 1984 ), the present study aimed to examine the potential effects of non-invasive, high and low frequency VNS in humans, with supplementary exploration of OFC activation using near-infrared spectroscopy (NIRS).…”

“…This study showed that the ipsilateral OB neurons exhibited an increase in firing activity under high frequency (80 Hz) VNS but not under low frequency (20–40 Hz) VNS. In subsequent studies, invasive VNS in human patients with medically intractable epilepsy (Kirchner et al, 2004 ) and therapy-resistant depression (Sperling et al, 2011 ), used low frequency stimulation, where no significant effects of VNS on functional olfactory tests were found. Indeed, research has not yet addressed the question of whether high frequency VNS, as demonstrated in previous research on animal models (García-Díaz et al, 1984 ), is capable of modulating the olfactory performance in humans.…”

VEP indices of cortical lateral interactions in epilepsy treatment

“…Electrophysiologic studies of the mechanism of action of VNS in humans have revealed no effect on EEG background (Hammond, Uthman, Reid, & Wilder, 1992a;Salinsky & Burchiel, 1993) or on standard visual, auditory, somatosensory, or P300 evoked potentials (Brazdil et al, 2001;Hammond, Uthman, Reid, & Wilder, 1992b;Uthman et al, 2004), although reduced spike duration and frequency has been observed (Koo, 2001) with chronic treatment. In a study of chemosensation effects with VNS treatment, the authors found prolonged P2 latencies of the olfactory event related potential (ERP) during the ON cycle of the stimulator suggesting a modulatory effect of VNS (Kirchner et al, 2004). However, none of these studies were specifically designed to look for effects of VNS on cortical lateral interactions, as we do here.…”