Ultrasonic Neuromodulation: Evidence from Neuron to Animal Model

Abstract

Neurostimulation is among the fundamental ways of neuroscience to probe the neural mechanisms from molecular to behavioral levels. The cutting-edge discovery of ultrasound as a non-invasive neurostimulation tool, has made possible for the effective amelioration of multiple functional brain diseases such as Parkinson disease, epilepsy and major depression. In this study, we highlight the up-to-date research on the application of the ultrasonic radiation force in the stimulation of isolated neuron, mice and monkeys with the underlying mechanism and the challenges of ultrasonic neuromodulation discussed. A high-frequency neurostimulation chip based on surface acoustic waves (SAWs) was designed and fabricated for the stimulation of isolated neuron. The responses of HEK cells, and neuron under the stimulation of the chip were recorded by the Ca2+ imaging and patch clamp. Confocal imaging of fluo-4-AM fluorescence was conducted on the neuron cells with the neurostimulation chip. The whole-cell voltage clamp was used to record the changes in membrane current in response to stimulation with the chip. Portable and wearable systems incorporating high voltage waveform generator (0.5-5MHz) were designed for free-moving small animal studies. In addition, a wearable 256-element 2D dual-curvature focused ultrasound phased-array transducer and MRI compatible ultrasonic neuromodulation system were developed for primate studies. Rhesus monkeys were trained to perform perceptual tasks with and without intermittent ultrasonic stimulation to specific cerebral cortex. In vivo single or multiple neuron electrode recording and eye tracking were conducted during task performance, allowing an evaluation of the direct linkage between physiology and behavior. Time-lapsed series of confocal images were obtained from neuron cells loaded with fluo-4-AM. Ca2+ transients were triggered in response to the stimulation by the high-frequency neurostimulation chip indicated by the increase in fluo-4 fluorescence intensity. Alterations in the membrane currents in response to high-frequency neurostimulation were recorded for HEK cells and neuron, respectively. Electromyography and local field potential signals were successfully recorded, demonstrating that the ultrasound neuromodulation can induce neuronal activity and evoke motor behaviors of animals. These results manifested that the interaction between ultrasonic radiation force and the protein of cell membranes may lead to the opening of mechanosensitive ion channels, thus triggering effective neuromodulation at both cellular and behavioral levels.