MRI-guided personalized tDCS planning for target engagement of the swallowing motor cortex after stroke: a finite-element modeling study

Background Poststroke dysphagia (PSD) is a common, debilitating consequence of stroke that affects up to 50% of patients and leads to multiple medical complications. Transcranial direct current stimulation (tDCS) therapeutic efficacy depends on the electrode montage and interindividual anatomical differences. The use of the standard C5/C6 placement based on 10–20 electroencephalography (EEG) coordinates to guide electrode placements may result in misalignment with the target position. Objective To investigate whether computational modeling leads to improved electric field (EF) parameters compared with those generated with standard electrode placement methods, and whether smaller sized electrodes can yield more focal results, we compared EF values across three tDCS montages targeting the cortical swallowing area (CSA): (i) optimized circular (Opt-C, 1.5 cm radius), (ii) EEG-based, conventional circular (Conv-C, 1.5 cm radius), and (iii) conventional square (Conv-S, 5 × 5 cm) electrode montages. Methods Structural MRI data from 50 PSD patients were analyzed. EF distributions were simulated using finite element method (FEM) analysis based on three-dimensional tetrahedral head models generated with the tES LAB 4.0 platform. Across montages, we compared EF strength, defined as the mean L2 norm of the EF (E norm ) across nodes within the target ROI, and target-specific focality, defined as the summed volume of target-ROI elements with E norm values at or above the 75th percentile of the corresponding whole-brain gray and white matter E norm distribution. Results Significant differences in EF strength ( p < 0.001) and target-specific focality ( p < 0.001) were identified across the three tDCS montages. The Opt-C montage produced the highest EF strength (median: 0.3525 V/m; IQR: 0.306–0.455) and target-specific focality (median: 104.69 mm 3 ; IQR: 88.17–120.31). Additionally, small circular electrodes resulted in significantly greater EF strength and target-specific focality than square electrodes ( p < 0.001). Conclusion MRI-guided personalized tDCS planning improved modeled EF delivery to the cortical swallowing target and revealed significant deviations from conventional C5/C6 placement in patients with severe PSD. These findings support image-guided target engagement as a framework for precision neuromodulation in PSD, while prospective physiological and clinical validation is required before therapeutic efficacy can be inferred.