ABSTRACT Posttraumatic Stress Disorder (PTSD) remains the most prevalent mental health (MH) diagnosis for first responders involved with responding to the 9/11 World Trade Center (WTC) terrorist attacks, with rates of PTSD much higher than that of the general population. There are a number of evidence-based treatments (EBT) for PTSD, with the strongest evidence base for trauma focused therapies, which typically require that patients engage with the index trauma and the associated fears and cognitions. This can be particularly difficult for PTSD patients for whom avoidance is a key symptom. Although these treatments are well supported, they are less effective in military and veteran populations in particular. Additionally, high dropout rates are observed across treatments for PTSD, with some studies yielding dropout rates of over 30%. Given the high rates of PTSD and the lower uptake of effective PTSD treatment among responders, there is a clear need to provide brief, easily accessible treatments to WTC responders to alleviate PTSD symptoms. There is a growing body of literature to support the use of vagus nerve stimulation (VNS) to treat a number of different disorders with promising animal model research regarding the use of VNS to address some of the features of PTSD, specifically, due to the impact that VNS has on key areas of the brain that are associated with fear extinction and hyperarousal in particular. The current study aims to determine whether the use of a novel, safe, non- invasive form of VNS, transcutaneous auricular VNS (taVNS), would be acceptable and feasible for use with WTC responders who have PTSD, and whether the methodology involved with a larger randomized controlled trial (RCT) to test taVNS efficacy would be acceptable and feasible. As such, the current study involves conducting a formative phase evaluation in the context of a focus group with WTC responders with elevated PTSD symptoms, in order to tailor the taVNS intervention and the pilot study methodology so that it’s relevant and acceptable for use. The taVNS intervention will then be piloted in a randomized, double-blind placebo controlled parallel-design study with 30 WTC responders affiliated with the Northwell Queens WTC Health Program who have PTSD. Outcomes include taVNS intervention and study methodology feasibility and acceptability. In addition, differences between baseline and post-treatment MH measures will be used to generate hypotheses for a future larger RCT aimed at evaluating taVNS efficacy in PTSD symptom reduction among a larger sample of WTC responders with PTSD. We will also use results to generate hypotheses regarding potential mechanisms of action including the various inflammatory, neural and cardiovascular changes that correlate with treatment outcomes. This pilot feasibility study is a first step toward bringing the latest advances in non-invasive, easy to use bioelectronic medicine technology to a population with high rates of PTSD who exper...