Hou Lin, Lei Yuming
Program of Motor Neuroscience, Department of Kinesiology & Sport Management, Texas A&M University, College Station, TX, 77843, USA.
Brain Stimul. 2025 Jul-Aug;18(4):1116-1130. doi: 10.1016/j.brs.2025.05.134. Epub 2025 May 23.
Low-intensity focused ultrasound offers deep tissue penetration and holds promise as a noninvasive tool for neuromodulating brain circuits. However, its effects on neural activity within the human spinal cord remain largely unexplored.
To investigate the effects of spinal cord ultrasound stimulation (SCUS) on corticospinal excitability by varying acoustic parameters: spatial-peak pulse-average intensity (I), duty cycle (DC), and pulse repetition frequency (PRF).
Two experiments were conducted involving 62 healthy adult participants. In Experiment 1 (N = 36), participants were randomly assigned to either a low-intensity group (2.5 W/cm, N = 18) or a relatively high-intensity group (10 W/cm, N = 18) to examine parameter-dependent SCUS effects. SCUS was delivered as a 500 ms pulse train to the C8 spinal cord segment using two DCs (10 % and 30 %) and two PRFs (500 and 1000 Hz). Stimulation was applied concurrently with posterior-anterior (PA) oriented transcranial magnetic stimulation (TMS) over the left primary motor cortex (M1), and motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle. Active and sham SCUS trials were interleaved and compared. In Experiment 2 (N = 26), the specificity of SCUS effects was assessed in relation to TMS coil orientation and target muscle using the sonication parameter set of 10 W/cm I, 1000 Hz PRF, and 30 % DC. MEPs from the FDI were recorded using anterior-posterior (AP) and latero-medial (LM) coil orientations, while MEPs from the abductor digiti minimi (ADM) muscle were assessed using PA, AP, and LM orientations. MEPs were also recorded from the biceps brachii with PA orientation. Active and sham SCUS conditions were interleaved and compared.
SCUS significantly suppressed MEP amplitudes compared to sham stimulation under relatively high-intensity (10 W/cm), high-PRF (1000 Hz) conditions, regardless of DC. No significant effects were observed at lower intensity (2.5 W/cm) or lower PRF (500 Hz). Follow-up experiments confirmed consistent inhibitory effects across multiple TMS coil orientations (PA, AP, LM) and in C8-innervated hand muscles (FDI and ADM), with no significant modulation observed in the more rostrally innervated biceps brachii muscle, supporting the specificity of C8-targeted SCUS.
These findings demonstrate that SCUS can modulate corticospinal excitability in a parameter-specific manner, with suppression observed primarily under relatively high-intensity and high-PRF conditions. SCUS represents a promising noninvasive technique for targeted neuromodulation of spinal neural circuits in humans.
低强度聚焦超声具有深层组织穿透能力，有望成为一种用于神经调节脑回路的非侵入性工具。然而，其对人类脊髓内神经活动的影响在很大程度上仍未得到探索。
通过改变声学参数：空间峰值脉冲平均强度（I）、占空比（DC）和脉冲重复频率（PRF），研究脊髓超声刺激（SCUS）对皮质脊髓兴奋性的影响。
进行了两项实验，涉及62名健康成年参与者。在实验1（N = 36）中，参与者被随机分配到低强度组（2.5 W/cm，N = 18）或相对高强度组（10 W/cm，N = 18），以检查参数依赖性SCUS效应。使用两种占空比（10%和30%）和两种脉冲重复频率（500和1000 Hz），将SCUS作为500 ms的脉冲串施加到C8脊髓节段。在左侧初级运动皮层（M1）上与后前（PA）方向的经颅磁刺激（TMS）同时施加刺激，并从右侧第一背侧骨间肌（FDI）记录运动诱发电位（MEP）。将主动和假SCUS试验交错进行并比较。在实验2（N = 26）中，使用10 W/cm I、1000 Hz PRF和30% DC的超声参数集，评估SCUS效应相对于TMS线圈方向和目标肌肉靶的特异性。使用前后（AP）和内外侧（LM）线圈方向记录FDI的MEP，同时使用PA、AP和LM方向评估小指展肌（ADM）的MEP。还使用PA方向记录肱二头肌的MEP。将主动和假SCUS条件交错进行并比较。
与假刺激相比，在相对高强度（10 W/cm）、高脉冲重复频率（1000 Hz）条件下，无论占空比如何，SCUS均显著抑制MEP波幅。在较低强度（2.5 W/cm）或较低脉冲重复频率（500 Hz）下未观察到显著影响。后续实验证实，在多个TMS线圈方向（PA、AP、LM）和C8支配的手部肌肉（FDI和ADM）中存在一致的抑制作用，而在更靠头端支配的肱二头肌中未观察到显著调节，这支持了以C8为靶点的SCUS的特异性。
这些发现表明，SCUS可以以参数特异性方式调节皮质脊髓兴奋性，主要在相对高强度和高脉冲重复频率条件下观察到抑制作用。SCUS是一种有前景的用于人类脊髓神经回路靶向神经调节的非侵入性技术。
