Program of Motor Neuroscience, Department of Kinesiology & Sport Management, Texas A&M University, College Station, Texas 77843.
Department of Neuroscience & Experimental Therapeutics, Texas A&M University, College Station, Texas 77843.
eNeuro. 2024 Mar 5;11(3). doi: 10.1523/ENEURO.0410-23.2024. Print 2024 Mar.
Touch sensation from the glabrous skin of the hand is essential for precisely controlling dexterous movements, yet the neural mechanisms by which tactile inputs influence motor circuits remain largely unexplored. By pairing air-puff tactile stimulation on the hand's glabrous skin with transcranial magnetic stimulation (TMS) over the primary motor cortex (M1), we examined the effects of tactile stimuli from single or multiple fingers on corticospinal excitability and M1's intracortical circuits. Our results showed that when we targeted the hand's first dorsal interosseous (FDI) muscle with TMS, homotopic (index finger) tactile stimulation, regardless of its point (fingertip or base), reduced corticospinal excitability. Conversely, heterotopic (ring finger) tactile stimulation had no such effect. Notably, stimulating all five fingers simultaneously led to a more pronounced decrease in corticospinal excitability than stimulating individual fingers. Furthermore, tactile stimulation significantly increased intracortical facilitation (ICF) and decreased long-interval intracortical inhibition (LICI) but did not affect short-interval intracortical inhibition (SICI). Considering the significant role of the primary somatosensory cortex (S1) in tactile processing, we also examined the effects of downregulating S1 excitability via continuous theta burst stimulation (cTBS) on tactile-motor interactions. Following cTBS, the inhibitory influence of tactile inputs on corticospinal excitability was diminished. Our findings highlight the spatial specificity of tactile inputs in influencing corticospinal excitability. Moreover, we suggest that tactile inputs distinctly modulate M1's excitatory and inhibitory pathways, with S1 being crucial in facilitating tactile-motor integration.
触觉感受来自手部的无毛发皮肤对于精确控制灵巧运动至关重要，但触觉输入影响运动回路的神经机制在很大程度上仍未得到探索。通过在手的无毛发皮肤上进行空气喷射触觉刺激，并在初级运动皮层（M1）上进行经颅磁刺激（TMS），我们研究了来自单个或多个手指的触觉刺激对皮质脊髓兴奋性和 M1 内皮质电路的影响。我们的结果表明，当我们用 TMS 靶向手部的第一背侧骨间肌（FDI）时，同域（食指）触觉刺激，无论其位置（指尖或基部）如何，都会降低皮质脊髓兴奋性。相反，异域（无名指）触觉刺激则没有这种效果。值得注意的是，同时刺激五个手指会导致皮质脊髓兴奋性的下降比刺激单个手指更为明显。此外，触觉刺激显著增加了皮质内易化（ICF）并降低了长间隔内皮质抑制（LICI），但不影响短间隔内皮质抑制（SICI）。鉴于初级体感皮层（S1）在触觉处理中的重要作用，我们还通过连续 theta 爆发刺激（cTBS）检查了下调 S1 兴奋性对触觉-运动相互作用的影响。在 cTBS 之后，触觉输入对皮质脊髓兴奋性的抑制作用减弱。我们的发现强调了触觉输入在影响皮质脊髓兴奋性方面的空间特异性。此外，我们认为触觉输入明显调节了 M1 的兴奋性和抑制性途径，而 S1 对于促进触觉-运动整合至关重要。
