Chen R, Garg R
Division of Neurology and The Toronto Western Hospital Research Institute, University Health Network, University of Toronto, Toronto, Ontario M5T 2S8, Canada.
J Neurophysiol. 2000 Mar;83(3):1426-34. doi: 10.1152/jn.2000.83.3.1426.
Transcranial magnetic stimulation (TMS) of the human motor cortex elicits direct and indirect (I) waves in the corticospinal tract. Facilitatory I wave interaction has been demonstrated with a suprathreshold first stimulus (S1) followed by a subthreshold to threshold second stimulus (S2). Intracortical inhibition (ICI) and intracortical facilitation (ICF) can be studied by another paired TMS paradigm with a subthreshold conditioning stimulus (CS) followed by a suprathreshold test stimulus. Facilitatory I wave interaction in motor representations other than the hand area and its relationship to ICI and ICF has not been studied. We studied I wave interaction, ICI and ICF in an intrinsic hand muscle (abductor pollicis brevis, APB), in a proximal arm muscle (biceps brachii, BB) and in a lower limb muscle (tibialis anterior, TA) in 11 normal subjects. I wave facilitation was studied by paired TMS at 24 interstimulus intervals (ISIs) from 0.5 to 5.1 ms. For APB and TA, facilitation occurred in three distinct peaks at ISIs of 0.9-1.7, 2. 5-3.5, and 4.1-5.1 ms. For BB, facilitation was significant for the first two peaks. The latencies of the peaks were similar among different muscles, but the magnitude of facilitation was much greater for APB and TA compared with BB. For all three muscles, changing the S2 to transcranial electrical stimulation (TES) resulted in much less facilitation of the first peak. For APB, there was significant I wave facilitation with S2 at 72% motor threshold (MT). The same stimulus used as the CS did not elicit ICF at ISI of 15 ms, suggesting that the threshold for eliciting I wave facilitation is lower than that for ICF. For BB and TA, there was no I wave facilitation with S2 at 90% of APB MT, and the same stimulus used as CS led to ICI. Thus in BB and TA the threshold for eliciting ICI is lower than that for I wave facilitation. We conclude that the circuits that mediate I wave interactions are present in the proximal arm and lower limb representations of the motor cortex. I wave facilitation occurs predominately in the cortex and may be primarily related to the monosynaptic corticomotoneuronal (CM) system. The reduced I wave facilitation for BB compared with APB and TA may be related to less extensive CM projection and involvement of other polysynaptic descending pathways. I wave facilitation, ICI, and ICF appears to be mediated by different neuronal circuits.
对人类运动皮层进行经颅磁刺激（TMS）可在皮质脊髓束中诱发直接波和间接（I）波。已证实，阈上的首个刺激（S1）之后紧跟阈下至阈上的第二个刺激（S2）时，会出现I波易化性相互作用。皮质内抑制（ICI）和皮质内易化（ICF）可通过另一种配对TMS范式进行研究，即阈下条件刺激（CS）之后紧跟阈上测试刺激。除手部区域外的其他运动代表区中的I波易化性相互作用及其与ICI和ICF的关系尚未得到研究。我们在11名正常受试者的手部固有肌（拇短展肌，APB）、近端臂肌（肱二头肌，BB）和下肢肌（胫前肌，TA）中研究了I波相互作用、ICI和ICF。通过配对TMS在0.5至5.1毫秒的24个刺激间隔（ISI）下研究I波易化。对于APB和TA，在0.9 - 1.7毫秒、2.5 - 3.5毫秒和4.1 - 5.1毫秒的ISI时出现三个不同的易化峰值。对于BB，前两个峰值的易化显著。不同肌肉的峰值潜伏期相似，但与BB相比，APB和TA的易化幅度要大得多。对于所有三块肌肉，将S2改为经颅电刺激（TES）会使第一个峰值的易化程度大大降低。对于APB，在72%运动阈值（MT）下，S2可产生显著的I波易化。在15毫秒的ISI时，用作CS的相同刺激未引发ICF，这表明引发I波易化的阈值低于引发ICF的阈值。对于BB和TA，在90%的APB MT时，S2未产生I波易化，且用作CS的相同刺激导致了ICI。因此，在BB和TA中，引发ICI的阈值低于引发I波易化的阈值。我们得出结论，介导I波相互作用的神经回路存在于运动皮层的近端臂部和下肢代表区中。I波易化主要发生在皮层，可能主要与单突触皮质运动神经元（CM）系统有关。与APB和TA相比，BB的I波易化程度降低可能与CM投射范围较小以及其他多突触下行通路的参与有关。I波易化、ICI和ICF似乎由不同的神经元回路介导。
