Wearable Transcranial Ultrasound System for Remote Stimulation of Freely Moving Animal

Objective: Transcranial focused ultrasound (tFUS) has drawn considerable attention in the neuroscience field as a noninvasive approach to modulate brain circuits. However, the conventional approach requires the use of anesthetized or immobilized animal models, which places considerable restrictions on behavior and affects treatment. Thus, this work presents a wireless, wearable system to achieve ultrasound brain stimulation in freely behaving animals. Methods: The wearable tFUS system was developed based on a microcontroller and amplifier circuit. Brain activity induced by tFUS was monitored through cerebral hemodynamic changes using near-infrared spectroscopy. The system was also applied to stroke rehabilitation after temporal middle cerebral artery occlusion (tMCAO) in rats. Temperature calculations and histological results showed the safety of the application even with prolonged 40 min sonication. Results: The output ultrasonic wave produced from a custom PZT transducer had a central frequency of 457 kHz and peak to peak pressure of 426 kPa. The device weight was 20 g, allowing a full range of motion. The stimulation was found to induce hemodynamic changes in the sonicated area, while open-field tests showed that ultrasound applied to the ipsilateral hemisphere for 5 consecutive days after the stroke facilitated recovery. Conclusion: The wearable tFUS system has been designed and implemented on moving rats. The results showed the ability of device to cause both short- and long lasting effects. Significance: The proposed device provides a more natural environment to investigate the effects of tFUS for behavioral and long-term studies.

I. Introduction

Noninvasive neuromodulation with high spatial specificity is valuable in the neuroscience field. Precise but invasive techniques such as deep brain stimulation have already been established as critical tools in the medical scenario [1]. Despite its significance, applications are limited due to the required surgical procedure. Transcranial electric and magnetic stimulation (TMS) were developed as alternative noninvasive tools for neurological disorders [2], [3] and post-stroke rehabilitation [4]. Still however, these techniques have low spatial resolution, only in the order of centimeters, and cannot easily reach deep brain regions beyond 5 cm in depth [5]–[7]. Novel neurostimulation techniques that can overcome these limitations are still in great demand.