Optimized tDCS for Targeting Multiple Brain Regions: An Integrated Implementation.

Transcranial direct current stimulation (tDCS) aims to deliver weak electric current into the brain to modulate neural activities. Based on the volume conductor model of the head, optimization algorithm can be used to determine a specific montage of high-definition electrodes on the scalp to achieve targeted stimulation. However, simultaneous targeting for multiple disconnected regions can rarely be found in the literature. Here we attempted to provide an integrated solution for optimized tDCS to target multiple brain regions (either a single point or brain structures). By improving the "maxintensity" routine previously published in [1], we are able to target two regions of interest (ROI) in the brain simultaneously.For ROIs more than two, we show that the "max-focality" algorithm using weighted least-square in [1] can be further improved by putting the L1-norm constraint on the stimulation current as apenalty term into the cost function. Up to five ROIs can be targeted at the same time without violating the safety criteria. Further analysis shows that, for multiple targets, a trade-off exists between targeting accuracy and the number of electrodes needed. We implemented all these algorithms in Soterix software HD-TargetsTM.