Do the Psychological Effects of Auricular Vagus Nerve Stimulation Depend on Gastrointestinal Response? Protocol for a Systematic Review and Meta-Analysis of Randomized Trials in Disorders of Gut–Brain Interaction

This review pools randomized trials of transcutaneous auricular vagus nerve stimulation (taVNS) in adults with disorders of gut–brain interaction (DGBI). It asks whether taVNS reduces anxiety and depression beyond sham or control stimulation, whether these psychological effects track or dissociate from gastrointestinal symptom response, and how the type of control and the rater (clinician vs patient) shape the estimated effect. Transparency statement: this is a retrospective registration. The protocol was written after the searches and a pilot extraction of psychological outcomes, and before any analysis; full extraction and analyses were completed before the registration was formally submitted.