Mechanisms of taVNS-induced working memory enhancement: a multimodal fNIRS-HRV-MEP study

Transcutaneous auricular vagus nerve stimulation (taVNS) has emerged as a promising neuromodulation technique for enhancing cognitive functions such as working memory (WM), yet its neural mechanisms remain unclear. In this study, fifty healthy young adults were randomly assigned to an active taVNS group or a sham group in a single-blind, sham-controlled design. Participants performed semantic and spatial 2-back WM tasks before and after stimulation. Hemodynamic activity was measured by functional near-infrared spectroscopy (fNIRS), autonomic activity was assessed by heart rate variability (HRV), and cortical excitability was indexed by central motor conduction time (CMCT) derived from single-pulse transcranial magnetic stimulation (TMS). Compared to sham, taVNS significantly accelerated reaction times across tasks and increased HRV metrics (HF, SDNN, RMSSD), indicating enhanced parasympathetic regulation. In addition, CMCT was shortened, reflecting improved corticospinal transmission efficiency. fNIRS revealed lateralized activation patterns, with greater hemodynamic engagement in regions corresponding to the left supramarginal gyrus (SMG.L) in semantic tasks and the putative right SMG (SMG.R) in spatial tasks. Mediation analyses suggested that HRV modulated semantic WM performance via SMG.L activation, while spatial WM performance was mediated by CMCT reduction. These findings support a neural resource allocation model in which taVNS facilitates WM through both domain-specific cortical modulation and enhanced efficiency in descending motor pathways, highlighting its potential as a non-invasive intervention to modulate brain-body interactions and enhance cognition.

The online version contains supplementary material available at 10.1007/s11571-026-10465-9.