Application Cases

Experiment Name: Comparative Study on Electromyographic Motor Thresholds Induced by Transcranial Magneto-Acoustic Stimulation and Transcranial Ultrasound Stimulation

Research Direction: Biomedical Engineering

Testing Equipment: ATA-4014 High-Voltage Power Amplifier, Signal Generator, Mobile Support, Rotating Tank, Permanent Magnet, Ultrasonic Transducer, Acoustic Collimator, Stereotaxic Apparatus, Multi-Channel Physiological Recorder

Figure: Block Diagram of the Experimental System

Experimental Procedure:
First, a pulse trigger signal with a specific repetition frequency was generated by a signal generator, which also produced pulse trains with specific amplitudes and widths. The modulated ultrasonic signal was amplified by the ATA-4014 high-voltage power amplifier to drive an ultrasonic transducer. This transducer was a planar type with a center frequency of 500 kHz and a bandwidth of 300 kHz. The ultrasonic waves emitted by the transducer were focused via an acoustic collimator to stimulate the target brain region of the experimental mouse. During the experiment, the mouse to be stimulated was fixed on a stereotaxic apparatus and subjected to mild gas anesthesia using a respiratory anesthesia machine. A permanent magnet with a surface magnetic induction intensity of 0.3 T was placed on a rotating mobile support beside the mouse to provide the static magnetic field required for the TMAS experiment. During the experiment, the application and removal of the magnetic field were controlled by rotating the support  to achieve TMAS and TUS processes on the mouse, respectively. The surface magnetic induction intensity of the permanent magnet was measured using a Gauss meter. Additionally, to determine the acoustic parameters in the experiment, an acoustic field detection device was set up. A needle hydrophone was used to detect the acoustic signal at the target stimulation region. This acoustic signal was displayed on a digital oscilloscope after passing through a variable gain amplifier. During the experiment, a multi-channel physiological electrical signal acquisition and processing system was used to collect, amplify, and perform  filtering on the mouse EMG. Subsequent analysis and processing of the EMG were performed using MATLAB toolboxes.

Figure: Relationship Between Mouse EMG and TMAS Excitation Signal

Experimental Results:
Based on the acquisition and analysis of mouse EMG and the determination of motor thresholds, this paper comparatively研究了 (研究了, studied) the regulatory effects of TUS and TMAS on motor cortex nerves. The results indicate that, compared to TUS, TMAS can induce EMG and allow detection of motor thresholds in mice at lower ultrasound intensities. Furthermore, under the same ultrasound intensity excitation, TMAS yields a higher success rate for inducing EMG and produces more stable motor feedback. These results suggest that TMAS possesses a more effective regulatory capacity over the mouse cerebral cortex motor area compared to TUS. The reason is that TMAS combines the composite stimulation of coupled electric and acoustic fields; the simultaneous presence of acoustic and electric fields forms a synergistic regulation.

Figure: Relationship Between Excitation Voltage and Acoustic Pressure at the Stimulation Target Site

Additionally, previous studies have shown that the minimum  ultrasound intensity Ispta capable of inducing motor feedback in mice under TUS is no less than 100 mW/cm². However, the results of this study indicate that TMAS can reduce the ultrasound intensity Ispta required to elicit motor feedback by approximately 80%. This can significantly reduce  potential damage to neural tissues caused by the thermal and cavitation effects of ultrasound. This finding is also of great significance for TUS research. Furthermore, this study observed that for TMAS, during a short period (3~10 s) following the introduction or removal of the magnetic field, the success rate of inducing mouse EMG was higher compared to during continuous magnetic field stimulation. This might be attributed to a certain magnetic effect on neuronal cells, altering their membrane conductivity or lowering the threshold potential. Additionally, this study only selected EMG as an evaluation  index . To further explore the impact of TMAS on neural electrical activity, future work could involve analyzing signals such as local field potentials and neuroelectrophysiology in mice to delve deeper into the stimulation principles and mechanisms of action of TMAS on neuronal cells.

Figure: ATA-4014C High-Voltage Power Amplifier Specifications and Parameters