Effect of stimulation frequency on hippocampal electric field induced by deep-brain magnetic stimulation

Deep-brain Magnetic Stimulation (DMS) is a noninvasive brain modulation method that improves hippocampal neural activity. The frequency of DMS has a significant effect on the hippocampal induced electric field. In this paper, we investigate the relationship between stimulation frequency and DMS-induced hippocampal electric field. The frequency sensitivity and distribution uniformity of the hippocampal electric field are calculated to quantify this relationship. The results show that the DMS-induced hippocampal electric field has a frequency-dependent property. The frequency sensitivity of the DMS-induced hippocampal electric field in the high frequency band is lower than that in the low frequency band, which corresponds to the low-pass filtering property of the neuron membrane. The frequency sensitivity of DMS-induced hippocampal electric field is highest in the range of 30–40 Hz. The uniformity of the hippocampal electric field induced by a single coil also reaches the highest in the range of 30–40 Hz, while uniformity of the hippocampal electric field induced by multiple-coil increases with increasing frequency. The frequency-dependent property of the DMS-induced hippocampal electric field is positively correlated with the quantity and size of coils, while negatively correlated with the spacing of the coils. This study is of great help in the selection of DMS frequencies and the design of coils.