Targeted nerve stimulation boosts movement-related brain activity in humans

The vagus nerve connects the brain to major organs throughout the body and plays important roles in many bodily functions. For people with mobility issues participating in physical therapy, stimulating the vagus nerve with a noninvasive technique-transcutaneous auricular vagus nerve stimulation, or taVNS-is emerging as an additional treatment intervention. But researchers have not assessed how taVNS interacts with motor systems during movement, which could inform treatment strategies for those with mobility issues. New from JNeurosci, Dane Donegan and Paulius Viskaitis at the Federal Institute of Technology Zurich led a study to advance understanding of how using taVNS as people move affects different systems in their brains and bodies. 

The researchers delivered short bursts of taVNS to 36 healthy volunteers as a computer system directed participants to tap or not tap their fingers at random intervals. Compared to no stimulation, movement-paired taVNS increased activity in a movement-related brain area. Pointing to the specificity of taVNS location, stimulating a different location with taVNS did not increase activity in the movement-related brain area. Pupil responses in the eye during movement-paired taVNS suggested that the neural signals were promoting an arousal state. Other nonmovement-related bodily measures were unchanged, suggesting that taVNS was distinctly targeting arousal and movement. To confirm this specific behavioral role of taVNS in movement, the researchers removed the voluntary component of the paradigm and used a different method to activate motor pathways in the brains of 19 unmoving participants while delivering taVNS. This manipulation triggered twitches in the finger without affecting other measures. 

According to the researchers, these findings reveal that using taVNS while people move may engage systems in the brain and body that are specific to movement rather than producing broad, nonspecific physiological effects. Viskaitis emphasizes treatment implications by presenting some of the questions the research team wants to address: "We want to know if any of these systems that taVNS interacts with are correlated with long-term outcomes. In other words, does this intervention lead to better motor performance? And hopefully we can eventually optimize [its use] by doing specific stimulations and tracking how the brain responds."