“Neuronavigated Transcranial Ultrasound Stimulation: ready for prime time?”
Ultrasonic neuromodulation has been demonstrated in rodents, non-human primates and healthy volunteers. We will first review the pioneering studies on transcranial ultrasonic neuromodulation. Transient effects (lasting less than 1s) were initially induced. The acoustical stimulation parameters were further optimized to extend the duration of the neuromodulation to several hours, in line with potential clinical applications. Nevertheless, the first proofs of concept on healthy volunteers were limited to cortical stimulation because of the defocusing effect of the human skull.
In parallel to these ultrasound neuromodulation studies, the rapid development of novel technologies enabling to focus precisely ultrasound beams through the human skull paved the way to noninvasive high precision deep brain stimulation with focused ultrasound. Transcranial focusing was initially achieved by using multi-element arrays made of hundreds of ultrasound transducers. But a disruptive approach was introduced recently: it consists in the use of a single-element transducer covered with a 3D printed acoustic lens. Altogether, the demonstration of sustained ultrasound neuromodulation and the development of precise, low cost and mobile prototypes for deed brain noninvasive ultrasound focusing indicate that Transcranial Ultrasound Stimulation is now ready for clinical translation.