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.

Low-intensity transcranial focused ultrasound (FUS) has emerged as a non-invasive brain stimulation modality that can reach deep brain areas with high spatial specificity. Previous studies have identified transient effects of FUS on the brain excitability and accompanying physiological responses. Yet the presence of long-lasting effects of FUS, which extend on the order of half an hour or more, has not been probed. We transcranially applied FUS to the somatosensory areas of the anesthetized rats for 10 min at a low duty cycle (5%) and intensity, far below the level that could alter the tissue temperature. Concurrently, we measured electroencephalographic (EEG) somatosensory evoked potentials (SEP) induced by the unilateral electrical stimulation of the hind limb before and after the sonication. Compared to the control sham condition that did not involve sonication, differential SEP features were evident and persisted beyond 35 min after the administration of FUS. The presence of this non-transient neuromodulatory effect may provide early evidence that FUS-mediated brain stimulation has the potential to induce neuroplasticity.

No abstract