Non-invasive vagus nerve stimulation improves sensory performance in humans

BACKGROUND: Accurate senses depend on high fidelity encoding by sensory receptors and error-free central processing in the brain. Progress has been made towards restoring damaged sensory receptors. However, methods for providing on demand treatment of impaired central sensory processing arising from factors including aging, neurological dysfunction, inattention, and fatigue are scarce. Recent studies have demonstrated that tonic vagus nerve stimulation in rodents can activate the locus coeruleus-norepinephrine system in the brain to improve sensory processing rapidly and continuously. HYPOTHESIS: We hypothesized that non-invasive neuromodulation via tonic transcutaneous vagus nerve stimulation (tVNS) improves sensory performance in humans. METHODS: Twenty-nine adults with no reported neurological dysfunction completed three sham-controlled experiments that measured effects of tVNS on sensory performance metrics (auditory gap detection, visual letter discrimination) and heart rate variability. Tonic tVNS was delivered continuously to cervical (neck) or auricular (ear) branches of the vagus nerve while participants performed psychophysics tasks or passively viewed a display without an accompanying task. RESULTS: Cervical tVNS improved auditory gap detection by 35% and visual letter discrimination by 20%, on average, relative to sham stimulation. Notably, participants with lower sensory performance during control conditions experienced larger tVNS-mediated improvements. Lastly, tVNS increased heart rate variability relative to sham stimulation during passive viewing, corroborating vagal engagement. CONCLUSION: We demonstrate that non-invasive vagus nerve stimulation improves sensory processing in neurotypical human adults. These findings substantiate foundational studies in rodents and position tVNS as a neuromodulation method for targeted and on-demand interventions of impairments associated with central sensory processing dysfunction.