School of Human Movement Studies, Centre for Sensorimotor Neuroscience, The Univ. of Queensland, Brisbane, Queensland, Australia 4072.
J Neurophysiol. 2012 Jan;107(1):306-14. doi: 10.1152/jn.00212.2011. Epub 2011 Oct 19.
The purpose of the current study was to investigate corticospinal contributions to locomotor drive to leg muscles involved in cycling. We studied 1) if activation of inhibitory interneurons in the cortex via subthreshold transcranial magnetic stimulation (TMS) caused a suppression of EMG and 2) how the responses to stimulation of the motor cortex via TMS and cervicomedullary stimulation (CMS) were modulated across the locomotor cycle. TMS at intensities subthreshold for activation of the corticospinal tract elicited suppression of EMG for approximately one-half of the subjects and muscles during cycling, and in matched static contractions in vastus lateralis. There was also significant modulation in the size of motor-evoked potentials (MEPs) elicited by TMS across the locomotor cycle (P < 0.001) that was strongly related to variation in background EMG in all muscles (r > 0.86; P < 0.05). When MEP and CMEP amplitudes were normalized to background EMG, they were relatively larger prior to the main EMG burst and smaller when background EMG was maximum. Since the pattern of modulation of normalized MEP and CMEP responses was similar, the data suggest that phase-dependent modulation of corticospinal responses during cycling in humans is driven mainly by spinal mechanisms. However, there were subtle differences in the degree to which normalized MEP and CMEP responses were facilitated prior to EMG burst, which might reflect small increases in cortical excitability prior to maximum muscle activation. The data demonstrate that the motor cortex contributes actively to locomotor drive, and that spinal factors dominate phase-dependent modulation of corticospinal excitability during cycling in humans.
本研究旨在探究皮质脊髓投射对参与踏车运动的腿部肌肉运动驱动的贡献。我们研究了：1）经颅磁刺激(subthreshold transcranial magnetic stimulation, TMS)是否能通过皮层抑制性中间神经元的激活抑制踏车运动中肌肉的肌电图(electromyography, EMG)；2）经 TMS 和颈髓刺激(cervicomedullary stimulation, CMS)刺激运动皮层时，响应在运动周期内是如何被调节的。低于皮质脊髓束激活阈强度的 TMS 可在大约一半的研究对象和踏车运动时的肌肉中诱发 EMG 抑制，同时在股外侧肌的匹配静态收缩中也能诱发 EMG 抑制。TMS 在运动周期内诱发的运动诱发电位(motor-evoked potential, MEP)的大小也存在显著的调制（P<0.001），这与所有肌肉的背景 EMG 变化密切相关（r>0.86；P<0.05）。当将 MEP 和 CMEP 的幅度与背景 EMG 归一化时，它们在主要 EMG 爆发前相对较大，而在背景 EMG 最大时相对较小。由于归一化 MEP 和 CMEP 响应的调制模式相似，数据表明，人类踏车运动中皮质脊髓反应的相位依赖性调制主要由脊髓机制驱动。然而，在 EMG 爆发前，归一化 MEP 和 CMEP 响应的促进程度存在细微差异，这可能反映了在最大肌肉激活之前皮质兴奋性的微小增加。数据表明，运动皮层主动参与运动驱动，而在人类踏车运动中，脊髓因素主导皮质脊髓兴奋性的相位依赖性调制。
