Exploring the Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation on Post-Stroke Oral Phase Dysphagia via Functional Near-Infrared Spectroscopy

Objective Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising non-invasive neuromodulation therapy for post-stroke neurological dysfunction, but its neurophysiological mechanism in improving oral phase dysphagia remains unclear. This study aimed to investigate the effects of taVNS combined with routine swallowing rehabilitation on swallowing function and cortical activation patterns in patients with post-stroke oral phase dysphagia using functional near-infrared spectroscopy (fNIRS), and to elucidate the potential neuromodulatory mechanism of taVNS. Methods A single-blind, randomized controlled trial was conducted on 40 patients with post-stroke oral phase dysphagia admitted to our hospital from July 2023 to January 2025. Patients were randomly assigned to the conventional Therapy group (n = 20, sham taVNS + routine swallowing rehabilitation) and the taVNS group (n = 20, real taVNS + routine swallowing rehabilitation) at a 1:1 ratio via lottery. The intervention lasted for 2 weeks (5 sessions/week, 30 min/session for rehabilitation, 25 min/session for taVNS). Swallowing function was assessed using the Standardized Swallowing Assessment (SSA), Oral Function Scale (OFS), and Swallowing-Quality of Life (SWAL-QOL) scale before and after intervention by the same blinded evaluator. fNIRS was used to detect cortical hemodynamic responses (oxyhemoglobin, HbO) during chewing and tongue tip sliding tasks, and the activation levels of the prefrontal cortex (PFC), premotor/supplementary motor cortex (PM), primary motor cortex (M1), and primary somatosensory cortex (S1) were quantified. NIRS-KIT and SPSS 27.0 were used for fNIRS data processing and statistical analysis, respectively. Results There were no significant differences in baseline clinical characteristics and swallowing function scores between the two groups (all p  > 0.05). After intervention, both groups showed significant improvements in SSA and OFS scores (all p  < 0.05); the taVNS group had a significant increase in SWAL-QOL scores ( p  < 0.05), while the conventional group had no significant change (p > 0.05). Intergroup comparison showed no significant differences in SSA and SWAL-QOL scores ( p  > 0.05), but the taVNS group had significantly higher OFS scores than the conventional group ( p  < 0.05). For fNIRS results, in the chewing task, both groups exhibited significantly enhanced activation in the right PFC (RPFC), left PM (LPM), and left M1 (LM1) after intervention (all p  < 0.05), and the taVNS group had significantly stronger LPM activation than the conventional group ( p  < 0.05). In the tongue tip sliding task, both groups showed significant activation enhancement in LPM, right PM (RPM), LM1, and right S1 (RS1) (all p  < 0.05); additionally, the taVNS group had significant activation increases in right M1 (RM1) and left S1 (LS1) ( p  < 0.05), with no significant intergroup differences in all brain regions ( p  > 0.05). No severe adverse events were observed in either group during the intervention. Conclusion taVNS combined with routine swallowing rehabilitation is safe and effective for post-stroke oral phase dysphagia, and has a superior effect on improving oral motor function compared with routine rehabilitation alone. The neurophysiological mechanism of taVNS may be related to the enhancement of LPM activation and the promotion of extensive bilateral activation in M1 and S1, which optimizes the activation intensity and pattern of the central swallowing motor-related cortex, thereby facilitating the recovery of oral phase swallowing function. A schematic diagram illustrating this proposed neurophysiological mechanism is presented in Fig. 6.