Using electromagnetic reciprocity and magnetic resonance current density imaging to fit multi-electrode montage for non-invasive brain stimulation

Non-invasive brain stimulation (NIBS) involves passing low currents through the brain where detectable effects on neuronal activity and cognitive function have been found due to small but effective voltage gradients brought about in the brain tissue. Although NIBS is a promising tool for inducing alteration of cortical excitability but it presents challenge in terms of optimization of the electrode placement and stimulation parameters, especially in cases of heterogeneously damaged cortical structures where getting accurate conductivity values for computational head-modeling is challenging. Moreover, the target in the brain for NIBS to facilitate a specific residual function may be unknown where electroencephalogram (EEG) source localization for related event related potential may play an important role. Therefore, in this theoretical study, we explored the possibility of using a lead-field based formulation of the electromagnetic reciprocity theorem to reciprocally energize the EEG electrodes in order to target the neural source of event related potentials during a functional task. Moreover, a Magnetic Resonance Current Density Imaging based method is proposed to determine subject-specific lead-field where it is postulated that such NIBS-based artificial subthreshold ephaptic feedback may facilitate cortical neural events (e.g., event related synchronization/desynchronization), which remains to be validated in future via human studies.