Electroceutical enhancement of self-compassion training using transcutaneous vagus nerve stimulation: results from a preregistered fully factorial randomized controlled trial

Transcutaneous vagus nerve stimulation (tVNS) combined with a brief self-compassion mental imagery training (SC-MIT) produced a larger acute increase in state self-compassion and mindfulness than either intervention alone in healthy adults. Over eight daily sessions, tVNS plus SC-MIT showed accumulating effects on mindfulness but not self-compassion. Self-criticism and attentional bias toward compassionate faces were influenced only by the type of imagery training, not by stimulation. Heart rate variability was unaffected by any condition. The findings suggest tVNS may enhance meditation-based psychotherapies, while oculomotor metrics appear sensitive to self-compassion training.

Study at a glance

Abstract

Abstract Background Physiological signals conveyed by the vagus nerve may generate quiescent psychological states conducive to contemplative practices. This suggests that vagal neurostimulation could interact with contemplative psychotherapies (e.g. mindfulness and compassion-based interventions) to augment their efficacy. Methods In a fully factorial experimental trial, healthy adults ( n = 120) were randomized to transcutaneous vagus nerve stimulation (tVNS) plus Self-Compassion-Mental-Imagery Training (SC-MIT) or alternative factorial combinations of stimulation (tVNS or sham) plus mental imagery training (MIT: SC-MIT or Control-MIT). Primary outcomes were self-reported state self-compassion, self-criticism, and heart rate variability (HRV). Exploratory outcomes included state mindfulness and oculomotor attentional bias to compassion-expressing faces. Most outcomes were assessed acutely on session 1 at the pre-stimulation (T1), peri-stimulation (T2), and post-MIT + stimulation (T3) timepoints, and after daily stimulation+MIT sessions (eight sessions). Results During session 1, a significant Timepoint × Stimulation × MIT interaction ( p = 0.025) was observed, reflecting a larger acute T1→T3 increase in state self-compassion after tVNS+SC-MIT, with similar rapid effects on state mindfulness. Additionally, significant Session × MIT and Session × Stimulation interactions ( p ≤ 0.027) on state mindfulness (but not self-compassion) suggested that tVNS+SC-MIT’s effects may accumulate across sessions for some outcomes. By contrast, changes in state self-criticism and compassion-related attentional bias were only moderated by MIT (not stimulation) condition. HRV was unaffected by stimulation or MIT condition. Conclusion tVNS augmented the effects of SC-MIT and might, therefore, be a useful strategy for enhancing meditation-based psychotherapies. Our findings also highlight the value of oculomotor attentional metrics as responsive markers of self-compassion training and the continued need for sensitive indices of successful vagal stimulation.