Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America.
Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America.
PLoS One. 2022 Apr 20;17(4):e0267268. doi: 10.1371/journal.pone.0267268. eCollection 2022.
Transcranial ultrasound stimulation (tUS) shows potential as a noninvasive brain stimulation (NIBS) technique, offering increased spatial precision compared to other NIBS techniques. However, its reported effects on primary motor cortex (M1) are limited. We aimed to better understand tUS effects in human M1 by performing tUS of the hand area of M1 (M1hand) during tonic muscle contraction of the index finger. Stimulation during muscle contraction was chosen because of the transcranial magnetic stimulation-induced phenomenon known as cortical silent period (cSP), in which transcranial magnetic stimulation (TMS) of M1hand involuntarily suppresses voluntary motor activity. Since cSP is widely considered an inhibitory phenomenon, it presents an ideal parallel for tUS, which has often been proposed to preferentially influence inhibitory interneurons. Recording electromyography (EMG) of the first dorsal interosseous (FDI) muscle, we investigated effects on muscle activity both during and after tUS. We found no change in FDI EMG activity concurrent with tUS stimulation. Using single-pulse TMS, we found no difference in M1 excitability before versus after sparsely repetitive tUS exposure. Using acoustic simulations in models made from structural MRI of the participants that matched the experimental setups, we estimated in-brain pressures and generated an estimate of cumulative tUS exposure experienced by M1hand for each subject. We were unable to find any correlation between cumulative M1hand exposure and M1 excitability change. We also present data that suggest a TMS-induced MEP always preceded a near-threshold cSP.
经颅超声刺激（tUS）作为一种非侵入性脑刺激（NIBS）技术具有很大的潜力，与其他 NIBS 技术相比，它提供了更高的空间精度。然而，其对初级运动皮层（M1）的报道效果有限。我们旨在通过在食指的紧张性肌肉收缩期间对 M1 的手部区域（M1hand）进行 tUS 来更好地了解 M1 中的 tUS 效应。选择在肌肉收缩期间进行刺激是因为存在经颅磁刺激诱导的皮质静默期（cSP）现象，其中 M1hand 的经颅磁刺激（TMS）会不由自主地抑制自愿运动活动。由于 cSP 被广泛认为是一种抑制现象，因此它是 tUS 的理想平行现象，tUS 通常被提议优先影响抑制性中间神经元。记录第一背侧骨间肌（FDI）的肌电图（EMG），我们研究了 tUS 刺激期间和之后肌肉活动的影响。我们没有发现 FDI EMG 活动与 tUS 刺激同时发生变化。使用单脉冲 TMS，我们发现稀疏重复 tUS 暴露前后 M1 的兴奋性没有差异。使用参与者结构 MRI 的声学模拟，我们根据实验设置匹配了模型中的内部压力，并为每个受试者生成了 M1hand 经历的累积 tUS 暴露量的估计。我们无法发现累积 M1hand 暴露量与 M1 兴奋性变化之间的任何相关性。我们还提供的数据表明，TMS 诱导的 MEP 总是先于接近阈值的 cSP。
