Transcutaneous auricular vagus nerve stimulation at 300 Hz increased pupil size at intensities between 2 and 4.8 mA, but not at higher intensities up to 8.1 mA.
Does 300 Hz transcutaneous auricular vagus nerve stimulation impact pupil size as a function of intensity?
300 Hz taVNS applied to the external acoustic meatus increases pupil size non-linearly, suggesting activation of the locus coeruleus-norepinephrine system at moderate but not high intensities.
Transcutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulatory technique that may have numerous potential health and human performance benefits. However, optimal stimulation parameters for maximizing taVNS efficacy are unknown. Progress is impeded by disagreement on the identification of a biomarker that reliably indexes activation of neuromodulatory systems targeted by taVNS, including the locus coeruleus-norepinephrine (LC-NE) system. Pupil size varies with LC-NE activity and is one potential taVNS biomarker that has shown inconsistent sensitivity to taVNS in prior studies. The present study examined the relationship between pupil size and taVNS using stimulation parameters that have shown promising behavioral effects in prior studies but have received comparatively little attention. Participants received trains of 50 μs taVNS pulses delivered continuously below perceptual threshold at 300 Hz to the left external acoustic meatus (EAM) while pupil size was recorded during a pupillary light reflex task. Analysis of pupil size using generalized additive mixed modeling (GAMM) revealed a non-linear relationship between taVNS intensity and pupil diameter. Active taVNS increased pupil size during stimulation for participants who received taVNS between 2 and approximately 4.8 mA, but not for participants who received higher-intensity taVNS (up to 8.1 mA). In addition, taVNS effects persisted in subsequent blocks, mitigating decreases in pupil size over the course of the task. These findings suggest 300 Hz taVNS activates the LC-NE system when applied to the EAM, but its effects may be counteracted at higher intensities.
Phillips et al. (Sat,) reported a other. Transcutaneous auricular vagus nerve stimulation (taVNS) was evaluated on Pupil size during a pupillary light reflex task. Transcutaneous auricular vagus nerve stimulation at 300 Hz increased pupil size at intensities between 2 and 4.8 mA, but not at higher intensities up to 8.1 mA.