Ultrasound neuromodulation (UNM), where a region in the brain is targeted by focused ultrasound (FUS), which, in turn, causes excitation or inhibition of neural activity, has recently received considerable attention as a promising tool for neuroscience. Despite its great potential, several aspects of UNM are still unknown. An important question pertains to the off-target sensory effects of UNM and their dependence on stimulation frequency. To understand these effects, we have developed a finite-element model of a mouse, including elasticity and viscoelasticity, and used it to interrogate the response of mouse models to focused ultrasound (FUS). We find that, while some degree of focusing and magnification of the signal is achieved within the brain, the induced pressure-wave pattern is complex and delocalized. In addition, we find that the brain is largely insulated, or ’cloaked’, from shear waves by the cranium and that the shear waves are largely carried away from the skull by the vertebral column, which acts as a waveguide. We find that, as expected, this waveguide mechanism is strongly frequency dependent, which may contribute to the frequency dependence of UNM effects. Our calculations further suggest that off-target skin locations experience displacements and stresses at levels that, while greatly attenuated from the source, could nevertheless induce sensory responses in the subject.

超声神经调节（UNM）是聚焦超声（FUS）针对大脑中的一个区域，进而引起神经活动的兴奋或抑制，最近作为一种有前途的神经科学工具受到了相当大的关注。尽管潜力巨大，但新墨西哥大学的几个方面仍然未知。一个重要的问题涉及 UNM 的脱靶感觉效应及其对刺激频率的依赖性。为了了解这些影响，我们开发了小鼠的有限元模型，包括弹性和粘弹性，并用它来询问小鼠模型对聚焦超声 (FUS) 的响应。我们发现，虽然大脑内实现了一定程度的信号聚焦和放大，但引起的压力波模式是复杂且离域的。此外，我们发现大脑在很大程度上与颅骨的剪切波隔离或“隐藏”，并且剪切波在很大程度上被充当波导的脊柱从颅骨中带走。我们发现，正如预期的那样，这种波导机制强烈依赖于频率，这可能导致 UNM 效应的频率依赖性。我们的计算进一步表明，偏离目标的皮肤位置经历的位移和应力水平虽然从源头大大减弱，但仍然可以引起受试者的感觉反应。