Replacing continuous stimulation of one set of electrodes with successive stimulation of multiple sets of electrodes can improve the focality of transcranial temporal interference stimulation (tTIS), especially the focality of stimulation towards deep brain regions: A simulation study.

Temporal interference (TI) stimulation has been proved to stimulate deep brain region while not activating the overlying cortex in the mouse brain. However, traditional TI, where two alternating currents with different frequencies are delivered by two electrode pairs, has poor focality in the human brain due to the high complexity of human brain structures, which limits the further application of TI. In traditional multipair TI, more than two alternating currents with different frequencies are injected by more than two electrode pairs at the same time. In this study, we proposed a novel multipair method which replaces continuous stimulation of one set of electrodes (eg: 1 montage for 30 minutes) with successive stimulation of multiple sets of electrodes (eg: 6 montages for 5 minutes each). By simulation using finite element method, we showed that this new method could improve the focality of TI in both neocortical regions and deep brain regions compared with traditional two-pair TI and the improvement was more significant in deep brain region. Ten realistic finite element models were used and five brain regions were tested (M1, DLPFC, ACC, NAc and hippocampus). It is expected that this new multipair TI can be used to improve the effectiveness of TI when researchers are translating TI from theoretical researches to clinical applications.