Vagal Nerve Stimulation for Interoception Modulation

We aim to assess and modulate gastric interoception in healthy adults using gastric and brain MRI, different meal volumes (Experiment 1), and transcutaneous auricular vagus nerve stimulation (taVNS) (Experiment 2). MR examinations will precede and immediately follow ingestion of a test meal (containing pineapple, with high manganese content, as a contrast agent), using real-time 3D cine MRI. Subjects will be scanned before ingestion and at 15, 45, and 75 minutes post-meal, in order to extract objective indices of gastric function. Functional MRI (fMRI) brain scans will be alternated to gastric MRI scans. Each subject will undergo 2 separate MRI visits, ingesting different doses of contrast meal in order to peripherally modulate gastric afference (Experiment 1), or receiving sham and active taVNS (Experiment 2), so to modulate visceral afference at the central level.Outcomes will assess the taVNS response of brainstem vagal neurocircuitry, as well as the impact of taVNS on fMRI connectivity patterns (fcMRI) of gastric afference, and link them to MRI-derived gastric outcomes, such as gastric emptying rate, gastric accommodation (fundic volumes), and gastric motility (peristaltic wave propagation).