Analysis of Electric Field in Hippocampus Induced by Temporal Interference Deep-brain Magnetic Stimulation (TI-DMS)

Deep-brain magnetic stimulation (DMS) has been shown to improve symptoms in Alzheimer's patients through inducing electric field in hippocampus. The strategy of temporal interference (TI) has been proven effective in trans cranial alternating current stimulation (tACS). In this study, we try the DMS combined with TI to induce an high frequency electric field containing low frequency components for hippocampus, which is named Temporal Interference Deep-brain Magnetic Stimulation (TI-DMS). We established a realistic head model based on MRI data, and designed two sets of coils based on the figure-8 coils. Through calculating the time-varying electric field, it is proved that TI-DMS is able to induce low-frequency envelope electric fields in the hippocampus. The power density is calculated to prove the power of the electric field is concentrated in the effective frequency component. Compared with DMS, it can be found that TI-DMS obtains a higher energy density in the effective frequency band by inducing a lower-amplitude envelope electric field. In the deep brain region where the hippocampus is located, the distribution of the envelope electric field induced by TI-DMS exhibits a focused characteristic, while the electric field induced by DMS is closer to a uniform distribution. The comparative study of two sets of coils shows that multi-coil array can also be applicated for TI-DMS, and it has a better performance than single-coil pair as a result of larger equivalent size. These results will facilitate the research on more complicated multi-coil for TI-DMS.