Effect of transcutaneous auricular vagus nerve stimulation (taVNS) on inhibitory control as a function of motor task complexity.

This study examined the effects of transcutaneous auricular vagus nerve stimulation (taVNS) on inhibitory control during motor tasks of varying complexity. Motor task complexity was manipulated in a Simon task using two approaches: (1) movement complexity, contrasting a simple lifting action with a more complex reaching action, and (2) movement type selection, contrasting both actions performed either in separate blocks or intermixed within the same block (non-active vs. active conditions). Heart rate variability indices were also recorded to assess potential autonomic effects of taVNS. It was hypothesized that taVNS would enhance inhibitory control under high-demand conditions, particularly during the active movement type selection condition, and that these behavioral effects would be accompanied by increased cardiac vagal activity. The results supported the first prediction: taVNS significantly improved inhibitory control in the active movement type selection condition. This improvement was reflected in a lower kinematic error rate and a smaller Simon effect during lifting actions, which became most demanding when performed alongside reaching due to their higher automaticity and susceptibility to impulsive errors. These behavioral benefits suggest that taVNS facilitated conflict-related control dynamics, thereby helping to limit impulsive motor activations and minimizing errors. In contrast, taVNS did not affect inhibitory control in the non-active movement type selection condition, emphasizing its context-dependent influence. Furthermore, taVNS did not alter heart rate variability, consistent with previous reports of variable autonomic responsiveness rather than peripheral vagal modulation. The findings highlight how taVNS facilitates adaptive inhibitory control in complex motor contexts.