Brasil-Neto J P, Cohen L G, Hallett M
Human Cortical Physiology Unit, Medical Neurology Branch, National Institutes of Health, Bethesda, Maryland 20892.
Muscle Nerve. 1994 Jul;17(7):713-9. doi: 10.1002/mus.880170702.
We have previously shown that the amplitudes of motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) were transiently decreased after exercise, indicating fatigue of motor pathways in the central nervous system. The responsible mechanism is apparently decreased efficiency in the generation of the descending volleys in the motor cortex. We also noted a progressive decrement in amplitude from the first to the fourth MEP. To further clarify the mechanism of this phenomenon, 5 subjects were studied with TMS delivered at the rates of 0.1, 0.15, 0.3, 1, 3, and 6 Hz. The effect was best demonstrated at 0.3 Hz, and occurred after both isometric and isotonic exercise. Three of the subjects also had 0.3-Hz percutaneous electrical stimulation of the brainstem, and a decrement in MEP amplitude did not occur. Further, the delivery of TMS during muscle contraction after muscle fatigue failed to produce a decrement. The results are similar to those found at the neuromuscular junction in myasthenia gravis and are consistent with a reduced safety factor of cortical synaptic transmission in central nervous system fatigue.
我们之前已经表明，经颅磁刺激（TMS）诱发的运动诱发电位（MEP）的幅度在运动后会短暂下降，这表明中枢神经系统中运动通路出现了疲劳。其负责机制显然是运动皮层中下行冲动发放的效率降低。我们还注意到从第一个MEP到第四个MEP，其幅度逐渐减小。为了进一步阐明这种现象的机制，对5名受试者进行了研究，以0.1、0.15、0.3、1、3和6赫兹的频率施加TMS。在0.3赫兹时这种效应最为明显，并且在等长运动和等张运动后均会出现。其中三名受试者还接受了0.3赫兹的经皮脑干电刺激，MEP幅度并未出现下降。此外，在肌肉疲劳后的肌肉收缩过程中施加TMS未能导致幅度下降。这些结果与重症肌无力患者神经肌肉接头处的情况相似，并且与中枢神经系统疲劳时皮质突触传递的安全系数降低一致。
