Characterization of Ultrasound Neurostimulation in Mice

The aim of this preclinical study was to highlight the influence of the ultrasonic frequency (sub-megahertz range versus over-megahertz range) and pressure on the efficacy of ultrasound neurostimulation (USNS), by targeting the motor cortex of mouse and assessing its motor responses (visually and with electromyography). In addition, the effect of the size of focal spot on the USNS was explored. The results showed that the success rate, a metric associated with the elicited motor responses, increased with peak negative pressure, independently from the used frequency, describing a sigmoid that reaches a plateau for the highest pressure values. Also, when frequency was increased from 0.5 to 1.5 MHz, it was shown that the peak negative pressure had to be enhanced for maintaining the same efficiency of neurostimulation. Finally, this study showed that the neurostimulation, at 0.5 MHz frequency and 160 ms pulse duration, was less efficient when the size of focal spot was smaller, for used pressures smaller than 300 kPa, suggesting the existence of a minimum size of the stimulated brain area to have an efficient USNS.