The Cranial Nerves and Electrical Stimulation

Cranial nerves provide afferent pathways that enable bottom-up modulation of central autonomic and cognitive neural pathways. Because these pathways project to brainstem nuclei such as the nucleus tractus solitarius and engage neuromodulatory systems, including the locus coeruleus, electrical stimulation offers a mechanistically grounded approach to influencing brain function. This thesis tested whether active transcutaneous auricular vagus nerve stimulation (taVNS) produces physiological responses indicative of parasympathetic engagement, defined as decreases in heart rate, increases in heart rate variability, and decreases in respiration relative to a dose-matched earlobe control condition. Using cardiac and respiratory measures as physiological markers, taVNS at the tragus was compared to an anatomically distinct earlobe control across multiple waveform conditions. Heart rate variability (HRV) showed selective modulation: the 25 Hz waveform increased HRV during tragus stimulation relative to control, consistent with parasympathetic engagement, whereas other waveforms did not. Respiration and heart rate had no significant effects. These findings indicate that vagal pathway activation depends on stimulation parameters and identify HRV as a sensitive marker of vagal parasympathetic modulation.