I. Introduction
Sound waves were first used to modulate neuronal activity in 1958 [1]. Since then, ultrasound (US) neuromodulatory effects have been demonstrated numerous times in multiple animal models [2], [3], [4], [5], [6], [7], [8], [9], including invoking auditory nerve responses [10], modifying nerve conduction [11], and inducing reproducible excitation of neuronal circuits in the motor cortex in excised rodent brains [12] and in live animals [13]. Currently, the technique is being explored in clinical studies of epilepsy, mood alteration, and disorders of consciousness [4], [14], [15], [16], [17]. US as a neuromodulation therapy has several unique advantages because it is: noninvasive; capable of reaching both shallow and deep brain locations; capable of focusing on a relatively small region of tissue; safe as currently used; and cost-effective. It, thus, provides a unique method of neuromodulation to complement others currently in use, such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (TDCS).