Transcutaneous Vagus Nerve Stimulation at Olfactory Bulb-Relevant Frequencies Modulates Human Olfactory Function.

Transcutaneous vagus nerve stimulation (tVNS) is a noninvasive technique that engages central neuromodulatory pathways and has been shown to modulate sensory processing across multiple modalities. Here, we investigated whether tVNS influences human olfactory perception. Sixty-seven healthy adults were assigned to one of two stimulation frequency groups, 25 Hz (beta) or 55 Hz (gamma), and each received 20 min of tVNS applied to the left cymba concha as well as a control condition with identical stimulation delivered to the left earlobe. Odor discrimination, odor intensity, and visual attention were assessed before and after stimulation. Gamma frequency tVNS significantly decreased odor discrimination performance, whereas beta frequency did not. Odor intensity ratings increased modestly following stimulation in both groups, with a stronger effect observed after gamma-frequency tVNS. There were no changes in visual attention, and the stimulation intensity, which was selected by the participant, was not associated with olfactory outcomes. These findings demonstrate that tVNS can modulate human olfactory processing in a frequency-dependent manner. The selective effect of gamma frequency, that is, the known processing frequency of the human olfactory bulb, implies inhibitory interneuron engagement in the olfactory bulb. These findings demonstrate that noninvasive tVNS can modulate human olfactory processing in a frequency-specific manner and highlight stimulation frequency as a critical parameter for future translational applications.