Transcutaneous vagus nerve stimulation enhances episodic memory across valences and memory stages

Background Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising non-invasive neuromodulation technique with the potential to enhance memory. However, the optimal timing of stimulation across memory stages—encoding, consolidation, and retrieval—remains unclear. Objective This study aimed to systematically investigate the effects of taVNS applied at three different stages of episodic memory processing. Methods A total of 90 healthy young adults (mean age = 23.71 ± 2.90) participated in a randomized, single-blind, within-subject, crossover experiment involving both active taVNS and sham stimulation conditions. Participants were assigned to receive stimulation during one of three memory stages. They learned emotional (positive and negative) and neutral pictures. Memory performance was assessed 24 h later through a free recall task. Mixed-effects logistic regressions were used to analyze the effects of stimuli valence, stimulation conditions and timing on memory performance. Results taVNS significantly enhanced memory recall compared to sham stimulation (χ 2 (1) = 22.1, p < 0.001), regardless of whether it was administered during encoding, consolidation, or retrieval (χ 2 (2) = 0.98, p = 0.6). Emotional stimuli (positive and negative) were better recalled than neutral ones (χ 2 (2) = 46.54, p < 0.001), but no interaction between valence and stimulation timing was observed. Conclusion taVNS enhances episodic memory across all stages of memory processing, likely through arousal-related mechanisms. These findings support taVNS as a flexible cognitive enhancement tool that might be promising for different clinical populations.