Optimized interferential electric fields for noninvasive deep focal brain stimulation

Synopsis: Interferential stimulation (IFS) has generated considerable interest recently because of its potential to achieve focal stimulation in deep brain areas. In principle one can deliver currents with more than the two pairs of electrodes conventionally used with IFS. However, at present there is no systematic approach to optimize the location and currents of the multiple electrodes. We formulate a rigorous optimization criterion of IFS to achieve maximal modulation (max-intensity) or most focal stimulation (max-focality). We solved the IFS optimization either analytically (for max-intensity) or numerically (for max-focality) and show that optimized IFS can achieve more focal stimulation compared to conventional stimulation without interferential fields, both at cortical surface and in deep brain.