Task-dependent cortical responses to peripheral and central neuromodulation during water and saliva swallowing after...

Post-stroke dysphagia is a common and serious complication. Neurorehabilitation strategies include peripheral neuromuscular electrical stimulation (NMES) and central transcranial direct current stimulation (tDCS), which operate via distinct bottom-up and top-down mechanisms, respectively. However, their differential effects on cortical hemodynamic responses during functionally distinct swallowing tasks remain poorly understood. This pilot study aimed to investigate the immediate modulatory effects of NMES and tDCS on cortical hemodynamics during different swallowing tasks in post-stroke patients using functional near-infrared spectroscopy (fNIRS).

Eleven patients with post-stroke dysphagia participated in this exploratory, within-subject, repeated-measures pilot study. A minimum 24-h washout period was maintained between sessions, and the order of intervention conditions was randomized using a computer-generated sequence. Cortical hemodynamic responses, measured by changes in oxygenated hemoglobin (ΔHbO₂), were monitored using a 56-channel fNIRS system. Each participant performed both water swallowing and saliva swallowing tasks under three randomized conditions: a no-stimulation baseline, peripheral stimulation (NMES applied to suprahyoid muscles), and central stimulation (bilateral anodal tDCS over the primary motor cortex). Task-related cortical hemodynamic responses and hemispheric lateralization were analyzed for key regions of interest.

The primary analysis identified significant Stimulation × Task interactions in the bilateral frontopolar cortex (FPC), including the ipsilesional FPC, F(2, 20) = 8.44, raw p = 0.002, q = 0.031, partial η² = 0.458, and the contralesional FPC, F(2, 20) = 7.42, raw p = 0.004, q = 0.031, partial η² = 0.426. Bonferroni-adjusted simple-effects analyses showed that, under tDCS, water swallowing elicited greater FPC responses than saliva swallowing in both the ipsilesional (p_adj = 0.020) and contralesional (p_adj = 0.008) FPC. During water swallowing, tDCS produced greater contralesional FPC responses than no stimulation (p_adj = 0.006), whereas during saliva swallowing, no stimulation produced greater bilateral FPC responses than tDCS (I-FPC: p_adj = 0.008; C-FPC: p_adj = 0.034) and greater ipsilesional FPC responses than NMES (p_adj = 0.043). Exploratory paired comparisons, with FDR correction applied within each comparison family, further showed that under the no-stimulation condition, saliva swallowing elicited greater bilateral FPC responses than water swallowing (I-FPC: q = 0.018; C-FPC: q = 0.024). Under NMES, water swallowing elicited greater ipsilesional FPC responses than saliva swallowing (q = 0.002). During saliva swallowing, tDCS was associated with greater ipsilesional SMA/PMC responses than NMES (q = 0.014).

Acute cortical hemodynamic responses varied according to the combination of stimulation condition and swallowing task, with the strongest evidence arising from the bilateral FPC Stimulation × Task interaction. These findings indicate task-dependent prefrontal hemodynamic responses but do not establish stimulation-specific efficacy, hemispheric reorganization, neuroplasticity, or therapeutic superiority. Larger sham-controlled studies are required to determine the reproducibility and clinical relevance of these acute fNIRS findings.

The trial is registered at the International Traditional Medicine Clinical Trial Registry (ITMCTR), Available at: https://itmctr.ccebtcm.org.cn/en/index.html, Identifier ITMCTR2025001814.