CLINICAL CORE Abstract The overarching goal of this REVEAL Project (Research Evaluating Vagal Excitation and Anatomical Linkages) is to distinguish the contributing roles of efferent versus afferent VNS modulation of multiple peripheral organs and their dependence on stimulation parameters such as frequency, current output, and duty cycle. We propose a Common Study Protocol (CSP) that is strategically designed to reveal specific VNS parameter settings that modulate the autonomic nervous system control of three physiological systems (cardiovascular, immune, and metabolic). The CSP is complemented with three ancillary projects: 1) in vivo human electrical stimulation and recordings of the vagus nerve; 2) measurements of gastric emptying and accommodation; and 3) unique assessment of high frequency stimulation settings on these four different systems with the IDE-regulated Microburst (LivaNova) that is not possible with the standard LivaNova VNS devices used in the CSP. We will conduct assessments on 144 mostly newly implanted VNS patients (newly implanted=96, previously implanted=48; evenly distributed across epilepsy or depression patients) with either a standard LivaNova clinical device (Sentiva for epilepsy and Symmetry for depression) or a novel LivaNova Microburst device. We will examine the acute and chronic effects of various VNS stimulus parameters by measuring the following: 1) Autonomic: MSNA, baroreflex sensitivity, cardiac sympathovagal tone, autonomic reflexes, autonomic stressors; 2) Cardiovascular: heart rate (time & amp; frequency analyses), blood pressure (time & amp; frequency analyses), ECG (time, frequency, features, nonlinear analyses), ECG electrical burden, cardiac mechanics (Echocardiography), respiratory sinus arrythmia; 3) Immune: cytokines, C reactive protein, cell counts, CyTOF; 4) Metabolic: routine clinical biomarkers (e.g., glucose, lipids, HbA1c), hormones (gut and adipose derived, e.g., insulin, glucagon), serum LC-MS/MS metabolomics, PBMC LC-MS/MS metabolomics. Through a rigorous and sophisticated study design with both newly and previously implanted VNS patients, a comprehensive battery of standard and leading-edge outcome measures, and the highest caliber of quality control and regulatory oversight, we will produce a first-of-its-kind data set to share rapidly and broadly to the neuroscience and autonomic clinical and research communities. These data will provide a multi-system view of the vagus nerve’s functional connectivity in humans, filling a critical knowledge gap and leading to new therapies and research.