Transcutaneous cervical vagus nerve stimulation (tcVNS) does not enhance learning and memory performance in a visual detection task

Complex changes in our society demand continuous skill development for personal and professional readiness. Transcutaneous cervical vagus nerve stimulation (tcVNS) has the potential to enhance learning by non-invasively delivering electrical pulses to the cervical branch of the vagus nerve. This study aimed to replicate a previous study on the effect of tcVNS on learning. Thirty-four participants completed a four-day training in visual detection and recognition of specific vehicles in Synthetic Aperture Radar (SAR) images. Participants received either active or sham tcVNS before and after training. Performance was assessed immediately post-training and 1-, 30-, and 60-days after the last training. Contrary to expectations, active stimulation did not improve learning, vigilance, or response inhibition compared to sham stimulation. Exploratory analyses suggested a negative association between stimulation intensity and learning outcomes, consistent with an inverted-U dose-response relationship suggesting overstimulation. The absence of physiological biomarkers leaves unresolved whether stimulation failed to engage the vagus nerve, engaged it sub-optimally, or engaged it without downstream cognitive benefits. These findings underscore the importance of parameter optimization and biomarker validation in tcVNS research. Rather than a failed replication, this study offers a cautionary lesson for the field: even seemingly minor methodological choices may critically shape cognitive outcomes.Trial registration. Registered 14/08/2023, registration number NL-OMON53198.