Department of Biomedical Sciences, University of Sassari, Sassari, Italy.
Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK.
J Physiol. 2022 Aug;600(15):3567-3583. doi: 10.1113/JP283137. Epub 2022 Jul 14.
Face muscles are important in a variety of different functions, such as feeding, speech and communication of non-verbal affective states, which require quite different patterns of activity from those of a typical hand muscle. We ask whether there are differences in their neurophysiological control that might reflect this. Fifteen healthy individuals were studied. Standard single- and paired-pulse transcranial magnetic stimulation (TMS) methods were used to compare intracortical inhibitory (short interval intracortical inhibition (SICI); cortical silent period (CSP)) and excitatory circuitries (short interval intracortical facilitation (SICF)) in two typical muscles, the depressor anguli oris (DAO), a face muscle, and the first dorsal interosseous (FDI), a hand muscle. TMS threshold was higher in DAO than in FDI. Over a range of intensities, resting SICF was not different between DAO and FDI, while during muscle activation SICF was stronger in FDI than in DAO (P = 0.012). At rest, SICI was stronger in FDI than in DAO (P = 0.038) but during muscle contraction, SICI was weaker in FDI than in DAO (P = 0.034). We argue that although many of the difference in response to the TMS protocols could result from the difference in thresholds, some, such as the reduction of resting SICI in DAO, may reflect fundamental differences in the physiology of the two muscle groups. KEY POINTS: Transcranial magnetic stimulation (TMS) single- and paired-pulse protocols were used to investigate and compare the activity of facilitatory and inhibitory intracortical circuits in a face (depressor anguli oris; DAO) and hand (first dorsal interosseous; FDI) muscles. Several TMS intensities and interstimulus intervals were tested with the target muscles at rest and when voluntarily activated. At rest, intracortical inhibitory activity was stronger in FDI than in DAO. In contrast, during muscle contraction inhibitory activity was stronger in DAO than in FDI. As many previous reports have found, the motor evoked potential threshold was higher in DAO than in FDI. Although many of the differences in response to the TMS protocols could result from the difference in thresholds, some, such as the reduction of resting short interval intracortical inhibition in DAO, may reflect fundamental differences in the physiology of the two muscle groups.
面部肌肉在多种不同的功能中起着重要作用，例如进食、言语和非言语情感状态的交流，这些功能需要与典型手部肌肉完全不同的活动模式。我们想知道它们的神经生理控制是否存在差异，而这种差异可能反映了这一点。本研究共纳入了 15 名健康个体。使用标准的单脉冲和双脉冲经颅磁刺激（TMS）方法，比较了两个典型肌肉（降口角肌，一种面部肌肉和第一背侧骨间肌，一种手部肌肉）的皮质内抑制（短程皮质内抑制（SICI）；皮质静息期（CSP））和兴奋性回路（短程皮质内易化（SICF））。降口角肌的 TMS 阈值高于第一背侧骨间肌。在一定强度范围内，静息 SICF 在降口角肌和第一背侧骨间肌之间没有差异，而在肌肉激活时，第一背侧骨间肌的 SICF 强于降口角肌（P=0.012）。在静息状态下，第一背侧骨间肌的 SICI 强于降口角肌（P=0.038），但在肌肉收缩时，第一背侧骨间肌的 SICI 弱于降口角肌（P=0.034）。我们认为，尽管 TMS 方案的许多反应差异可能源于阈值的差异，但有些差异，例如降口角肌静息 SICI 的降低，可能反映了两组肌肉生理学的根本差异。关键点：使用经颅磁刺激（TMS）单脉冲和双脉冲方案，研究并比较了面部（降口角肌；DAO）和手部（第一背侧骨间肌；FDI）肌肉的易化和抑制性皮质内回路的活动。在目标肌肉休息和主动收缩时，测试了几种 TMS 强度和刺激间隔。在休息时，第一背侧骨间肌的皮质内抑制活性强于降口角肌。相比之下，在肌肉收缩时，降口角肌的抑制活性强于第一背侧骨间肌。与许多之前的报道一样，降口角肌的运动诱发电位阈值高于第一背侧骨间肌。尽管 TMS 方案的许多反应差异可能源于阈值的差异，但有些差异，例如降口角肌静息短程皮质内抑制的降低，可能反映了两组肌肉生理学的根本差异。
