Noninvasive neurostimulation on mice by 5 MHz ultrasound

Ultrasound has been demonstrated to be an effective approach for noninvasive neurostimulation. Low frequency ultrasound (<1 MHz) is preferable as its low ultrasonic attenuation when passing through the skull. High frequency ultrasound is able to provide reduced size of focal region. However, the performance of stimulation with high frequency ultrasound is not proved yet. This study examines the feasibility and effectiveness of using high frequency, i.e. 5 MHz, focused ultrasound to perform the neurostimulation on mice. The acoustic properties of 1 MHz and 5 MHz ultrasound on mouse skull were evaluated by a 3D acoustic scanning system. By performing proper acoustic compensation, 1 MHz and 5 MHz ultrasound can present the same acoustic intensity level after passing the skull. They were used to do the brain stimulation with same group of mice. Electromyography (EMG) signals collected from tail muscles and videos of motion responses were analyzed for the evaluation of neurostimulation. The results illustrated that 5 MHz ultrasound can successfully achieve the neurostimulation by monitoring the EMG and motion responses. The equivalent diameter (D) of stimulus for 5 MHz is significantly smaller than that of 1 MHz. Focused ultrasound with higher frequency can provide smaller size of stimulation region, which offers precise control of the neurostimulation in a non-invasive manner.