Imaging Brain Fluids During Breathing

This study will perform magnetic resonance imaging (MRI) measurements of hemodynamics and cerebrospinal fluid flow across breathing tasks and during breath-locked neuromodulation.

Inclusion Criteria: * Adult age 18-70 years Exclusion Criteria: * No ferrous metal implanted in head or body * No history of major head trauma * No neurological or psychiatric disorder * Not using medication that affects brain function * No implanted electronic devices (e.g. pacemaker) * No implant that poses an MR contraindication * Not pregnant, suspect they are pregnant, or seeking to become pregnant * Not claustrophobic * No piercings or jewelry that cannot be removed * Does not weigh more than 250 pounds * Normal or contact-corrected normal vision Exclusion for transcutaneous vagus nerve stimulation (tVNS) arm: * Conditions of skin or anatomy that affect left auricle or forehead skin and could impact placement of electrodes for tVNS or forehead stimulation * Diagnosis of significant cardiovascular or cerebrovascular disease \[e.g. congestive heart failure, stroke, cardiac conduction disorders (including: bundle branch block, heart block, long Q-T syndrome), history of asystole or non-sustained ventricular tachycardia. * Bradycardia (defined as resting heart rate \