Localizing Target for Transcranial Direct Current Stimulation in Drug-Resistant Epilepsy using Dynamic EEG Source Network

Epilepsy is a brain network disorder characterized by recurrent seizures. Transcranial direct current stimulation (tDCS) shows promise for treating drug-resistant epilepsy. The placement of the tDCS cathodal electrode is primarily on the scalp over the suspected epileptogenic zone; quantitative analysis is needed to support the selection. Additionally, identifying a target is difficult for patients with unclear focus or negative MRI findings. To address these issues, we proposed a non-invasive method to localize the target for tDCS based on the epileptogenic network. Interictal scalp EEG was used to estimate brain connectivity in the source space. To evaluate the effect of stimulation, we introduced a dynamic EEG source network for target localization based on neural mass models and the connectivity matrix. SimNIBS simulations further optimized the target location. Intracranial EEGs from 18 patients with drug-resistant epilepsy were used, and the forward-projected scalp EEGs were employed to validate our procedure rigorously. The results showed that the localized target overlapped with the resected brain area in 80% of seizure-free patients but in only 37.5% of non-seizure-free patients. This suggests that our proposed procedure can effectively localize the epileptogenic brain tissue. SimNIBS-based simulations further confirmed the significant reduction in seizure likelihood with cathodal stimulation at the target location compared to non-target locations. The results also showed that the signal-to-noise ratio significantly affects performance, underscoring the importance of selecting an interictal, low-noise segment. The proposed procedure offers a noninvasive, quantitative approach to tDCS target localization.