Comparison of optimized interferential stimulation using two pairs of electrodes and two arrays of electrodes

Interferential stimulation (IFS) or Temporal Interference (TI) has recently generated considerable interest as computational models show that it can focally stimulate deep brain regions with non-invasive transcranial electrical currents [1]. However, the proposed solution in [1] requires two arrays, involving dozens of electrodes in each, to achieve optimal focality in the deep brain regions. Implementation of this approach is usually not feasible in practice due to the limited number of channels and the associated accuracy and precision needed in current stimulation devices. Alternative method [2] focuses on using only two pairs of electrodes as proposed in the conventional IFS approach and searching exhaustively in the parameter space for the optimal montage that maximizes the focality of the modulation at the deep target. Here we compare these two methods in terms of the quality of the solutions (focality versus modulation depth) and the practicality (speed and number of electrodes needed). We then give general guidelines for optimal IFS in practice for future studies.