Diagnostic Ultrasound Modulates Human Motor Cortex: Neurophysiological Evidence from Paired-Pulse TMS and Computational Modelling
Matteo Guidetti, Sara Annaloro, Silvia Gallucci, Marta Parazzini, Emma Chiaramello, Amedeo Grado, Sara Marceglia, Nicola Morelli, Matteo Bologna, Alberto Priori, Tommaso Bocci
2026 · 10.21203/rs.3.rs-9029217/v1
Abstract
Background Transcranial ultrasound (tUS) represents a promising brain stimulation technique, yet its physiological effects using standard diagnostic protocols remain poorly characterized. This study examines the impact of conventional diagnostic ultrasound (dUS) on intracortical excitability. Methods Healthy subjects received 30 minutes of transcranial ultrasound (2.0 MHz) over the right motor cortex. Cortical excitation and inhibition were assessed bilaterally via paired-pulse TMS, quantifying resting motor threshold (RMT), short intracortical inhibition (SICI), intracortical facilitation (ICF) and long intracortical inhibition LICI before and after stimulation. The vasomotor reserve (through the breath-holding index) was also assessed. A computational model was developed to confirm the spatial selectivity of our protocol. Non-parametric and Bayesian analyses were used. Results Sixteen healthy adults (mean age 31.9 ± 11.0 years) were enrolled. dUS induced a significant reduction in SICI in the stimulated hemisphere (p = 0.016; Bayes Factor BF = 7.65), and a robust increase in LICI in the control hemisphere (p = 0.010; BF = 7.88). Between hemispheres, SICI was higher in the stimulated than in the control side (p = 0.046; BF = 3.90), while LICI was greater in the control hemisphere (p = 0.015; BF = 10.06). ICF, RMT and BHI showed no significant changes (all p > 0.05). Conclusions dUS elicits focal changes in cortical excitability, towards an overall excitatory effect, in the absence of detectable vascular changes. The observed changes also engage compensatory transcallosal mechanisms, likely involving GABA-B-mediated pathways within the contralateral hemisphere. These findings provide mechanistic evidence supporting further translational investigation.
Abstract via europepmc.
Exposures
Exposure 1: Diagnostic transcranial ultrasound (dUS) over right primary motor cortex
Target: primary motor cortex — “right motor cortex (M1)”
Device: not reported · linear phased-array probe (2.0 MHz) ✓
| Waveform | not reported | |
|---|---|---|
| Fundamental frequency (kHz) | 2,000 | ✓✓✓ |
| Pulse duration (ms) | not reported | |
| Pulse repetition frequency (Hz) | not reported | |
| Duty cycle (%) | not reported | |
| Sonication duration (s) | 1,800 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Patients underwent 30 min of sonication delivered through the right trans-temporal window to target M1 using a linear probe (2.0 MHz), using the same parameters routinely employed for diagnostic Transcranial Colour-coded (Duplex) Sonography (TCCS). Active stimulation was delivered over one hemisphere (stimulated hemisphere, SH), while sham stimulation was delivered over the contralateral hemisphere (control hemisphere, CH), with the order of treatment and the stimulated side pseudo-randomized across participants. SICI, ICF and LICI were assessed before (T0) and immediately after (T1) the 30-minute intervention in both hemispheres.
Flags from extraction
randomised— The stimulated side/order was 'pseudo-randomized across participants', but the paper explicitly states it follows 'guidelines for reporting non-randomised studies'; recorded as false based on the study's own classification of itself.sham_type— The mechanism of sham delivery to the control hemisphere (e.g. probe powered off, aimed away, or simply not applied) is not described; recorded as 'other'.exposures[0]— No numeric acoustic pressure or intensity (kPa or W/cm2) is reported for the diagnostic ultrasound exposure in the main text; only a simulated, normalized acoustic intensity distribution (percentage of local maximum) is given.exposures[0].timing.waveform— Diagnostic ultrasound (TCCS) inherently uses pulsed imaging sequences, but no PRF, duty cycle, or pulse duration is stated in the text, so waveform is left not_reported rather than inferred.exposures[0].target— Sonication was delivered through the right trans-temporal window, but the 'stimulated hemisphere' (which received active insonation) was pseudo-randomized across participants, so laterality of the actual active target may vary by participant despite the text describing a fixed right-sided window.