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

Background: Olfactory and gustatory functions were investigated before and during vagus nerve stimulation (VNS) in a group of 9 patients with therapy-resistant depression, implanted with a VNS system. Methods: Gustation and olfaction were tested using standard sniffing tests. Subjects participated in 2 sessions with the vagal stimulator switched on and off, respectively. Results: Under conditions of stimulation of the VNS, there were statistically significant differences of the threshold of perception, with an intensification of the taste sweet (Z = -2.0; p = 0.048) and bitter (Z = -2.5; p = 0.011) compared to the off-mode. A statistical trend (Z = -1.7; p = 0.098) for increased intensity of the taste salty was observed, however, these results would supposedly disappear after correction for multiple testing presumably due to the large number of variables and the small sample size. There were no statistically relevant differences concerning olfactory perception. Conclusions: The changes of gustatory perception under conditions of vagal nerve stimulation observed in this study show another important central nervous effect of vagal stimulation on the limbic system that might be of importance in the elucidation of mechanisms of action of VNS especially on refractory depression.