Transcranial focused ultrasound stimulation of motor cortical areas in freely-moving awake rats
Wonhye Lee, Phillip Croce, Ryan W. Margolin, Amanda Cammalleri, Kyungho Yoon, Seung-Schik Yoo
BMC Neuroscience 2018, 19 · 10.1186/s12868-018-0459-3
Abstract
Background Low-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. Results We 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. Conclusions The 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.
Abstract via europepmc.
Exposures
Exposure 1: tFUS to motor cortical areas (tail/limb/whisker representations), compared across awake and anesthetized states
Target: motor cortex — “motor cortical areas (tail, limb, and whisker motor representations)”
Device: custom-built · in-house-built miniature wearable FUS transducer (PZT ceramic element, American Piezo Ceramics)
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 600 | ✓✓✓ |
| Pulse duration (ms) | 1 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 500 | ✓✓✓ |
| Duty cycle (%) | 50pulse duration × PRF gives 50% | ✓✓✓ |
| Sonication duration (s) | 0.3 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | ⚑ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | deratingmean or range across subjects | |
| In-situ pressure (kPa) | 670 | ✓✓✓⚑ |
| In-situ Isppa (W/cm²) | 2.3, 14.9swept | ✓✓✓⚑ |
| In-situ Ispta (W/cm²) | 7.5 | ✓✓✓ |
Pulsed sonication (PRF 500 Hz, 1 ms tone-burst duration, 50% duty cycle, 300 ms sonication duration) with 5-10 s inter-stimulation interval; 10 sonication events per session, three repeated sessions per experimental condition (awake, ketamine/xylazine anesthesia, isoflurane anesthesia) with at least 48 h between sessions. Acoustic output was individually titrated per rat/condition to find the minimum intensity eliciting motor responses; off-target sonications (including unilateral auditory areas) were also delivered as a spatial-specificity control.
Flags from extraction
n_sessions_per_subject— Paper states three repeated tFUS sessions per experimental condition (awake, ketamine/xylazine, isoflurane); a single total across all three conditions per rat is not explicitly stated (would be ~9).exposures[0].in_situ.isppa_w_cm2— Range spans three different physiological conditions (awake, ketamine/xylazine, isoflurane) with different response thresholds, not a single systematic sweep at one state.exposures[0].in_situ.pressure_kpa— Value (0.67 MPa) and the paired Ispta value are drawn from a correlated triplet given for the specific 14.9 W/cm2 Isppa condition (the upper end of the intensity range used) in the Safety section, not for the full range of intensities used in the study.exposures[0].free_field.isppa_w_cm2— Stated in the transducer characterization section as the device's maximum output capability; not explicitly labeled as a free-field (water tank) versus in-situ (post-skull) measurement, but appears in the context of the pre-derating device characterization, distinct from the sonication-parameters section that explicitly discusses skull derating.