Transcranial focused ultrasound stimulation of motor cortical areas in freely-moving awake rats

Abstract

BackgroundLow-intensity transcranial focused ultrasound (tFUS) has emerged as a new non-invasive modality of brain stimulation with the potential for high spatial selectivity and penetration depth. Anesthesia is typically applied in animal-based tFUS brain stimulation models; however, the type and depth of anesthesia are known to introduce variability in responsiveness to the stimulation. Therefore, the ability to conduct sonication experiments on awake small animals, such as rats, is warranted to avoid confounding effects of anesthesia.ResultsWe developed a miniature tFUS headgear, operating at 600 kHz, which can be attached to the skull of Sprague–Dawley rats through an implanted pedestal, allowing the ultrasound to be transcranially delivered to motor cortical areas of unanesthetized freely-moving rats. Video recordings were obtained to monitor physical responses from the rat during acoustic brain stimulation. The stimulation elicited body movements from various areas, such as the tail, limbs, and whiskers. Movement of the head, including chewing behavior, was also observed. When compared to the light ketamine/xylazine and isoflurane anesthetic conditions, the response rate increased while the latency to stimulation decreased in the awake condition. The individual variability in response rates was smaller during the awake condition compared to the anesthetic conditions. Our analysis of latency distribution of responses also suggested possible presence of acoustic startle responses mixed with stimulation-related physical movement. Post-tFUS monitoring of animal behaviors and histological analysis performed on the brain did not reveal any abnormalities after the repeated tFUS sessions.ConclusionsThe wearable miniature tFUS configuration allowed for the stimulation of motor cortical areas in rats and elicited sonication-related movements under both awake and anesthetized conditions. The awake condition yielded diverse physical responses compared to those reported in existing literatures. The ability to conduct an experiment in freely-moving awake animals can be gainfully used to investigate the effects of acoustic neuromodulation free from the confounding effects of anesthesia, thus, may serve as a translational platform to large animals and humans.Electronic supplementary materialThe online version of this article (10.1186/s12868-018-0459-3) contains supplementary material, which is available to authorized users.

Focused ultrasound excites neurons via mechanosensitive calcium accumulation and ion channel amplification

“…2c). These results confirm that temperature does not play a role in ultrasonic neuromodulation in this parameter range, as predicted by numerical estimates (Constans et al, 2018;Lee et al, 2018). Among the potential non-thermal effects of ultrasound, bubble formation and cavitation have been hypothesized as a mechanism for ultrasonic neuromodulation due to the observation of enhanced responses at lower frequencies (Tyler, 2011).…”

“…To ensure that our results are relevant for in vivo scenarios, we took care to culture neurons on an acoustically transparent substrate and confirmed that our ultrasound conditions elicited responses under both 2D and 3D culture conditions. Indeed, key features of the cultured neuron response to ultrasound matched those observed in vivo (King et al, 2013;Lee et al, 2018;Lee et al, 2016a;Lee et al, 2016b;Sharabi et al, 2018;Wattiez et al, 2017), including response latency and the range of responsive ultrasound intensities.…”

Remote, brain region–specific control of choice behavior with ultrasonic waves

“…Anesthesia dampens neuronal excitability and susceptibility to stimulation. Both the anesthesia level ( 41 ) and the kind of anesthesia ( 42 ) affect ultrasound-mediated responses, and some authors claim responses only under specific anesthesia conditions ( 8 , 11 ). There may even be little or no neuromodulatory effects under anesthesia ( 14 , 15 ).…”

Microelectromechanical Systems-Based Neurotools for Non-Invasive Ultrasound Brain Stimulation

“…Most of the previous works demonstrated ultrasound neuromodulation on immobile or sedated animals because commercially available transducers are often bulky, heavy, and requires a collimator [19][20][21][22][23][24][25]. Recently, three pioneering works on MEMS-based ultrasound transducers have successfully demonstrated in vivo neuromodulation in freely-moving behaving animals [38][39][40][41]. The first of these reports was based on a CMUT ring array composed of 32 elements with a 183-kHz resonant frequency [38,39].…”

“…The other two works were based on piezoelectric transducers (Table 1) [40,41]. Lee et al [41] developed a miniaturized tFUS system for freely-moving animals. The transducer was about 6 g in weight and packaged in a three-dimensional-printed wearable headgear.…”