Roy Francois D, Norton Jonathan A, Gorassini Monica A
Department of Biomedical Engineering and Centre for Neuroscience, University of Alberta, Edmonton, Canada.
J Neurophysiol. 2007 Aug;98(2):657-67. doi: 10.1152/jn.00197.2007. Epub 2007 May 30.
Changes in the strength of corticospinal projections to muscles in the upper and lower limbs are induced in conscious humans after paired associative stimulation (PAS) to the motor cortex. We tested whether an intervention of PAS consisting of 90 low-frequency (0.1-Hz) stimuli to the common peroneal nerve combined with suprathreshold transcranial magnetic stimulation (TMS) produces specific changes to the motor-evoked potentials (MEPs) in lower leg muscles if the afferent volley from peripheral stimulation is timed to arrive at the motor cortex after TMS-induced firing of corticospinal neurons. Unlike PAS in the hand, MEP facilitation in the leg was produced when sensory inputs were estimated to arrive at the motor cortex over a range of 15 to 90 ms after cortical stimulation. We examined whether this broad range of facilitation occurred as a result of prolonged subthreshold excitability of the motor cortex after a single pulse of suprathreshold TMS so that coincident excitation from sensory inputs arriving many milliseconds after TMS can occur. We found that significant facilitation of MEP responses (>200%) occurred when the motor cortex was conditioned with suprathreshold TMS tens of milliseconds earlier. Likewise, it was possible to induce strong MEP facilitation (85% at 60 min) when afferent inputs were directly paired with subthreshold TMS. We argue that in the leg motor cortex, facilitation of MEP responses from PAS occurred over a large range of interstimulus intervals as a result of the paired activation of sensory inputs with sustained, subthreshold activity of cortical neurons that follow a pulse of suprathreshold TMS.
在对清醒人类的运动皮层进行配对联想刺激（PAS）后，其上下肢肌肉的皮质脊髓投射强度会发生变化。我们测试了一种PAS干预措施，即对腓总神经进行90次低频（0.1赫兹）刺激并结合阈上经颅磁刺激（TMS），如果外周刺激的传入冲动在TMS诱发皮质脊髓神经元放电后定时到达运动皮层，是否会对小腿肌肉的运动诱发电位（MEP）产生特定变化。与手部的PAS不同，当估计感觉输入在皮质刺激后15至90毫秒的范围内到达运动皮层时，腿部会产生MEP易化。我们研究了这种广泛的易化是否是由于阈上TMS单脉冲后运动皮层阈下兴奋性延长所致，从而使得TMS后数毫秒到达的感觉输入的同步兴奋能够发生。我们发现，当运动皮层在数十毫秒前接受阈上TMS预处理时，MEP反应出现显著易化（>200%）。同样，当传入输入与阈下TMS直接配对时，也有可能诱发强烈的MEP易化（60分钟时为85%）。我们认为，在腿部运动皮层，PAS引起的MEP反应易化在很大的刺激间隔范围内发生，这是由于感觉输入与阈上TMS脉冲后皮质神经元持续的阈下活动配对激活所致。
