Transcranial focused ultrasound modulates cortical and thalamic motor activity in awake sheep
Hyun-Chul Kim, Wonhye Lee, Jennifer Kunes, Kyungho Yoon, Ji Eun Lee, Lori Foley, Kavin Kowsari, Seung-Schik Yoo
Scientific Reports 2021, 11 · 10.1038/s41598-021-98920-x
Abstract
Transcranial application of pulsed low-intensity focused ultrasound (FUS) modulates the excitability of region-specific brain areas, and anesthetic confounders on brain activity warrant the evaluation of the technique in awake animals. We examined the neuromodulatory effects of FUS in unanesthetized sheep by developing a custom-fit headgear capable of reproducibly placing an acoustic focus on the unilateral motor cortex (M1) and corresponding thalamic area. The efferent responses to sonication, based on the acoustic parameters previously identified in anesthetized sheep, were measured using electromyography (EMG) from both hind limbs across three experimental conditions: on-target sonication, off-target sonication, and without sonication. Excitatory sonication yielded greater amplitude of EMG signals obtained from the hind limb contralateral to sonication than that from the ipsilateral limb. Spurious appearance of motion-related EMG signals limited the amount of analyzed data (~ 10% selection of acquired data) during excitatory sonication, and the averaged EMG response rates elicited by the M1 and thalamic stimulations were 7.5 ± 1.4% and 6.7 ± 1.5%, respectively. Suppressive sonication, while sheep walked on the treadmill, temporarily reduced the EMG amplitude from the limb contralateral to sonication. No significant change was found in the EMG amplitudes during the off-target sonication. Behavioral observation throughout the study and histological analysis showed no sign of brain tissue damage caused by the acoustic stimulation. Marginal response rates observed during excitatory sonication call for technical refinement to reduce motion artifacts during EMG acquisitions as well as acoustic aberration correction schemes to improve spatial accuracy of sonication. Yet, our results indicate that low-intensity FUS modulated the excitability of regional brain tissues reversibly and safely in awake sheep, supporting its potential in theragnostic applications.
Abstract via europepmc.
Exposures
Exposure 1: Excitatory and suppressive sonication of M1
Target: primary motor cortex — “unilateral primary motor cortex (M1)”
Device: Ultran · Ultran Group · GPS200-D40-FL57-MR ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 250 | ✓✓✓ |
| Pulse duration (ms) | 0.5 | ✓✓✓ |
| Pulse repetition frequency (Hz) | not reported | |
| Duty cycle (%) | 70, 5swept | ✓✓✓ |
| Sonication duration (s) | 0.2, 60swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | deratingsingle value | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | 5.2, 20.5, 1.5, 4.7, 5.3, 13.7swept | ✓✓✓⚑ |
| In-situ Ispta (W/cm²) | 3.6, 14.4, 0.1, 0.2, 0.3, 0.7swept | ✓✓✓ |
In detail, for the excitatory sonication, 200-ms sonication duration, 0.5-ms tone-burst duration (TBD), and 70% duty cycle (DC) were used. For the suppressive sonication, 1-min sonication was given using 0.5-ms TBD and 5% DC. Excitatory sonication was given at Isppa of 5.2 W/cm2 (N=6 sheep; 3.6 W/cm2 Ispta) or 20.5 W/cm2 (N=4; 14.4 W/cm2 Ispta); suppressive sonication was given at Isppa of 1.5 (N=1; 0.1 W/cm2 Ispta), 4.7 (N=2; 0.2 W/cm2 Ispta), 5.3 (N=6; 0.3 W/cm2 Ispta) or 13.7 W/cm2 (N=1; 0.7 W/cm2 Ispta). Excitatory sonication was delivered at intervals of 5 s while the sheep stayed still; suppressive sonication was delivered for one minute while the sheep walked on a treadmill.
Exposure 2: Excitatory and suppressive sonication of thalamus
Target: thalamus — “corresponding thalamic area”
Device: Ultran · Ultran Group · GPS200-D40-FL57-MR ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 250 | ✓✓✓ |
| Pulse duration (ms) | 0.5 | ✓✓✓ |
| Pulse repetition frequency (Hz) | not reported | |
| Duty cycle (%) | 70, 5swept | ✓✓✓ |
| Sonication duration (s) | 0.2, 60swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | deratingsingle value | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | 5.2, 20.5, 1.5, 4.7, 5.3, 13.7swept | ✓✓✓⚑ |
| In-situ Ispta (W/cm²) | 3.6, 14.4, 0.1, 0.2, 0.3, 0.7swept | ✓✓✓ |
In detail, for the excitatory sonication, 200-ms sonication duration, 0.5-ms tone-burst duration (TBD), and 70% duty cycle (DC) were used. For the suppressive sonication, 1-min sonication was given using 0.5-ms TBD and 5% DC. The same in situ intensity levels used for M1 sonication (Isppa 5.2/20.5 W/cm2 excitatory; 1.5/4.7/5.3/13.7 W/cm2 suppressive) applied across the excitatory/suppressive thalamic sessions.
Flags from extraction
exposures[0].in_situ.isppa_w_cm2— Intensity list combines both excitatory (5.2, 20.5 W/cm2) and suppressive (1.5, 4.7, 5.3, 13.7 W/cm2) sonication values, each used in different sheep subsets (N given per value in the source quote); array order does not align positionally with duty_cycle_pct/sonication_duration_s arrays. Full correspondence is given in protocol_description.exposures[1].in_situ.isppa_w_cm2— Same intensity values as reported for M1 are assumed to also apply to thalamic sonication since the paper describes a single shared sonication protocol per animal across both targets; not explicitly re-stated per target.timing.pulse_repetition_frequency_hz— PRF is not stated numerically in the main text for either excitatory or suppressive sonication; only duty cycle and tone-burst duration are given, and PRF would require arithmetic to derive.