This Anchillary project uses a refined technique of ultrasound-guided microneurography of the human cervical vagus nerve, an approach developed by Professor Vaughan Macefield and used safely to-date in 44 prior study participants. The overall goal of this project is to build upon prior data obtained using this approach by undertaking a detailed neurophysiological investigation of the human vagus nerve and to identify the nerve fibers activated during vagal nerve stimulation (VNS) in participants with implanted VNS devices in response to different stimulation parameters. In addition to providing data in unprecedented detail into the physiology of the human vagus nerve, this project will investigate different stimulus intensities, durations and frequencies that differentially excite myelinated and unmyelinated nerve fibers. These results will inform the CSP and guide future development of novel neural interfaces for VNS for various clinical applications.