Comparative Study of Transcranial Magneto-Acoustic Stimulation and Transcranial Ultrasound Stimulation of Motor Cortex.

Transcranial ultrasound stimulation (TUS; <i>f</i> < 1 MHz) is a promising approach to non-invasive brain stimulation. Transcranial magneto-acoustic stimulation (TMAS) is a technique of neuromodulation for regulating neuroelectric-activity utilizing a magnetic-acoustic coupling electric field generated by low-intensity ultrasound and magnetic fields. However, both techniques use the physical means of low-intensity ultrasound and can induce the response of the motor cortex. Therefore, it is necessary to distinguish the difference between the two techniques in the regulation of neural activity. This study is the first to quantify the amplitude and response latency of motor cortical electromyography (EMG) in mice induced by TMAS and TUS. The amplitude of EMG (2.73 ± 0.32 mV) induced by TMAS was significantly greater than that induced by TUS (2.22 ± 0.33 mV), and the EMG response latency induced by TMAS (101.25 ± 88.4 ms) was significantly lower than that induced by TUS (181.25 ± 158.4 ms). This shows that TMAS can shorten the response time of nerve activity and enhance the neuromodulation effect of TUS on the motor cortex. This provides a theoretical basis for revealing the physiological mechanisms of TMAS and the treatment of neuropsychiatric diseases using it.

Introduction

Purpose Transcranial ultrasound stimulation

Study Objective To quantitatively compare the amplitude and response latency of motor cortical electromyography (EMG) in mice induced by transcranial magneto-acoustic stimulation (TMAS) versus transcranial ultrasound stimulation (TUS).

Animal model / Human subject Mice (C57BL/6, sex: male, age: 7-8 weeks)

Disease model healthy

Targeted brain region(s) Motor Cortex

Target coordinates 3.5 mm to the left of the midline of the ear and 7.5 mm behind it

Outcomes and Safety

Summary of Outcomes TMAS produced stronger and faster motor cortex responses than TUS—significantly higher EMG amplitude and shorter latency—when delivered with 500 kHz ultrasound (300 pulses, 1 kHz PRF, 400 NTB, T = 4 s) at Psptp = 83 kPa and 38 kPa and under isoflurane ≤ 0.5% (no significant advantage at 21 kPa or 0.6%).

Safety-related matter The authors state that their ultrasound parameters are below US FDA diagnostic safety limits and emphasize the need to identify safe TUS parameters and minimize ultrasound intensity; they report TMAS achieves modulation at low intensity (MI = 0.12, Ispta = 288.9 mW/cm^2), suggesting improved safety. No adverse effects or harms to animals are reported in the paper.

Brain Region

Ultrasound Parameters

Ultrasound instrument Planar ultrasonic transducer (V301, Olympus, Japan)

FUS Frequency 0.5 MHz

FUS Intensity ISPTA: 288.9 mW/cm2

FUS Pressure 0.083, 0.038, 0.021

FUS Mode pulsed

Pulse duration 0.6 ms

Duration of a single FUS session 4 s

Focal Characteristics focal length: 2 mm

Treatment frequency single

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