Author: Maharjan A1, Peng M2, Cakmak YO1,3,4
Affiliation: <sup>1</sup>Department of Anatomy, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.
<sup>2</sup>Department of Food Science, University of Otago, Dunedin, New Zealand.
<sup>3</sup>Brain Health Research Centre, Division of Sciences, University of Otago, Dunedin, New Zealand.
<sup>4</sup>Medical Technologies Centre of Research Excellence, Auckland, New Zealand.
Conference/Journal: Front Hum Neurosci.
Date published: 2019 Jan 21
Other:
Volume ID: 12 , Pages: 533 , Special Notes: doi: 10.3389/fnhum.2018.00533. eCollection 2018. , Word Count: 317
Median nerve stimulation (MNS) had been performed in the existing literature to alleviate symptoms of nausea and vomiting. The observed facilitative effects are thought to be mediated by the vagal pathways, particularly the vagus nerve (VN) brainstem nuclei of the dorsal motor nucleus of vagus and nucleus tractus solitarius (DMV-NTS). Sense of smell is one of the major sensory modalities for inducing vomiting and nausea as a primary defense against potentially harmful intake of material. This study aimed to test effects of non-invasive, high and low frequency MNS on human olfactory functioning, with supplementary exploration of the orbitofrontal cortex (OFC) using near-infrared spectroscopy (NIRS). Twenty healthy, male, adults performed supra-threshold odor intensity tests (labeled magnitude scale, LMS) for four food-related odorant samples (presented in three different concentrations) before and after receiving high-, low frequency MNS and placebo (no stimulation), while cortical activities in the OFC was monitored by the NIRS. Data of the NIRS and LMS test of separate stimulation parameters were statistically analyzed using mixed-model analysis of variance (ANOVA). Only the high frequency MNS showed effects for suppressing the intensity perception of the moderate concentration of Amyl Acetate (p:0.042) and strong concentration of Isovaleric Acid (p:0.004) and 1-Octen-3-ol (p:0.006). These behavioral changes were coupled with significant changes in the NIRS recordings of the left (p:0.000) and right (p:0.003) hemispheric orbitofrontal cortices. This is the first study that applied non-invasive, high frequency MNS to suppress the supra-threshold odor ratings of specific concentrations of odors. The vagal networks are potential relays of MNS to influence OFC. Results from the current article implore further research into non-invasive, high frequency MNS in the investigation of its modulatory effects on olfactory function, given its potential to be used for ameliorating nausea and malnutrition associated with various health conditions.
KEYWORDS: labeled magnitude scale; median nerve stimulation; nausea and vomiting; near-infrared spectroscopy; non-invasive electrostimulation; olfaction; orbitofrontal cortex
PMID: 30719001 PMCID: PMC6348262 DOI: 10.3389/fnhum.2018.00533