Researchers at the University of Tartu and Leiden University report that pulsed transcutaneous auricular vagus nerve stimulation (taVNS) can produce pupil dilation in rapid, intermixed trial designs, but the effect depends on pulse duration and the sham location. The findings appear in Psychophysiology (April 2026).

The team ran two experiments. In Experiment 1 (N = 40) they intermixed active taVNS and earlobe sham pulses of 3.4 seconds and found inconclusive evidence for increased pupil dilation with taVNS. In Experiment 2 (N = 60) they used 1.0-second taVNS pulses and observed a strong pupil response — but only for the group that received sham at the earlobe. When sham stimulation was applied to the upper scapha, a non-vagal control area with a similar density of sympathetic fibers, the taVNS effect disappeared.

The authors also tested whether delivering pulses during exhalation would amplify the pupil response, which would be expected if the effect followed the vagus nerve → nucleus tractus solitarius → locus coeruleus pathway. They saw no enhancement during exhalation. Based on these patterns, the paper cautions that taVNS-evoked pupil dilation may not reliably indicate activation of vagal afferent pathways.

The study shows pulsed taVNS can work in intermixed, event-related designs used by cognitive neuroscientists, but it raises questions about mechanism and about choice of sham site. The paper is available in Psychophysiology (DOI: 10.1111/psyp.70302).

Photo credit: cdn.ncbi.nlm.nih.gov

Tags: taVNS, pupil dilation, vagus nerve, sham control, respiration

Topics: Vagus nerve & taVNS, Neuromodulation, Non-invasive brain stimulation