Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Response Inhibition

Response inhibition, which immediately stops an ongoing action, is important for daily life activities. Noradrenaline (NA), a neurotransmitter, is reportedly involved in response inhibition. In recent years, transcutaneous auricular vagus nerve stimulation (taVNS) has gained attention for its ability to induce NA release in various areas of the brain. Thus, taVNS can potentially improve response inhibition, but this has not been confirmed. The present study investigated the effects of taVNS on response inhibition by measuring salivary alpha-amylase (sAA), an indirect indicator of NA. This study implemented a crossover design, with 22 healthy men (age, 21.4 ± 1.7 years) performing a stop signal task and undergoing sAA measurement before and after the taVNS intervention. taVNS was performed for 30 min at an intensity midway between the sensory and pain thresholds. Participants underwent two stimulation conditions, namely taVNS targeting the left concha and sham stimulation targeting the left earlobe, in a randomized order. Response inhibition was evaluated by comparing the stop signal reaction time (SSRT) before and after taVNS intervention. Under taVNS, sAA levels significantly increased after stimulation. However, no significant difference in SSRT was observed between before and after the intervention under either condition. These results suggest that taVNS increases sAA levels after stimulation, but it does not influence response inhibition, suggesting that the modulation of NA by taVNS is not sufficient to improve response inhibition.