I. Introduction
Transcranial magneto-acoustic stimulation (TMAS) [1], a noninvasive neural regulation technique [2], [3], acts deeply on the brain via a magneto-acoustic coupling effect [4] and is characterized by high penetration depth and good focusing [5]–[7] of low intensity focused ultrasound (LIFU) [8]. The spatial resolution of the electric field induced by TMAS is determined by the spatial resolution of the focused ultrasound [9], and the focal spot diameter can be less than 3 mm [10]. Thus, TMAS has higher spatial resolution than transcranial magnetic stimulation (TMS) [11] or transcranial direct current stimulation (tDCS) [12]. TMAS can therefore obtain better positioning accuracy and target stimulation effects than the other approaches, while ensuring appropriate depth of stimulation. It provides a new approach to transcranial nerve stimulation, especially when investigating brain functional regions with high requirements for targeted and deep brain stimulation. It is potentially valuable for both disease treatment [13], [14] and brain function research [15]–[17]. However, neurons are preferentially sensitive to modulated low-frequency oscillation [18] rather than high-frequency oscillation [19]. High-frequency ultrasound is used in TMAS in order to ensure penetration and focusing of the neural stimulus in the tissue [20]. However, it is difficult to use TMAS to create the modulated low-frequency currents that stimulate neurons most strongly.