Individualized Targeting and Optimization of Multi-channel Transcranial Direct Current Stimulation in Drug-Resistant Epilepsy

The principle of epilepsy surgery in patients with drug-resistant focal epilepsy is to localize and then to resect the epileptogenic zone. However, epilepsy surgery might not be feasible if a cortical malformation or focal cortical dysplasia (FCD), is located very close to eloquent areas of the brain. Non-invasive brain stimulation is a promising technique for modulating brain activity and may become a neurotherapeutic approach for suppressing long term epileptic seizures. In the present study, we optimize a multi-channel transcranial direct current stimulation (tDCS) montage based on Electro-(EEG) and Magneto-Encephalography (MEG) source analysis for the therapeutic stimulation of a patient with drug-resistant epilepsy due to an FCD located very close to Broca's area. We first construct a realistic volume conductor Finite Element Method (FEM) model of the patient's head, including skull defects, calibrated skull conductivities and white matter conductivity anisotropy. Single modality (EEG or MEG) and combined EEG/MEG (EMEG) source analysis is performed for localizing the irritative zone that caused interictal epileptic discharges (IEDs). We then adopt a novel optimization algorithm, Alternating Direction Method of Multipliers (ADMM), in order to optimize the multichannel tDCS montage for distributing the injected currents in the target brain region. The patient's source analysis indicates localizations very close to the FCD and orientations to a different cortical side depending on the used measurement modality. The resulting tDCS optimized montage is based on the source reconstruction which is closer to the FCD and the occurred stimulation montage is focal over the detected FCD. The combination of individual source analysis for targeting and optimization algorithms for the estimation of a tDCS montage is a promising neurotherapeutic approach of suppressing long term epileptic seizures.