Cortical facilitation assessed with triad conditioning transcranial magnetic stimulation has been termed triad-conditioned facilitation (TCF). TCF has been supposed to reflect increased intracortical facilitation (ICF) at short interstimulus intervals (ISI) around 10 ms and an intrinsic rhythm of the motor cortex at longer ISI around 25 ms. To gain further insight into the pathophysiological mechanism of TCF, we systematically studied the effect of suprathreshold conditioning stimulus (CS) and test stimulus (TS) intensity on TCF. Various CS intensities and TS intensities were used in a triad-conditioning paradigm that was applied to 11 healthy subjects. ISI between pulses were studied between 5 and 200 ms. TCF at 10 ms ISI enhanced with increasing CS intensity but decreased with increasing TS intensity. The duration of facilitation was longer with higher CS intensity. However, TCF at 25 ms ISI could not be elicited with none of the CS and TS intensities addressed here. Our results are consistent with the notion of TCF at short ISI reflecting ICF. The enhanced and prolonged facilitation with increase of CS without additional isolated facilitation at longer ISI suggest a prolongation of ICF.

中文翻译：

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使用三联条件经颅磁刺激条件调节和测试刺激强度对皮层兴奋性的影响。

经三联条件经颅磁刺激评估的皮质促进作用已被称为三联条件促进作用（TCF）。据推测，TCF会在10毫秒左右的短刺激间隔（ISI）反映出皮质内促进作用（ICF）的增加，而在25毫秒左右的较长ISI反映出运动皮层的固有节律。为了进一步了解TCF的病理生理机制，我们系统地研究了阈上条件刺激（CS）和测试刺激（TS）强度对TCF的影响。在适用于11位健康受试者的三重条件调节范例中使用了各种CS强度和TS强度。在5到200 ms之间研究了脉冲之间的ISI。ISI在10毫秒时的TCF随着CS强度的增加而增强，但随着TS强度的增加而减小。CS强度越高，促进时间越长。但是，在此处未涉及CS和TS强度的情况下，无法在25 ms ISI时引发TCF。我们的结果与短期ISI中反映ICF的TCF概念一致。随着CS的增加，增强和延长的促进作用在更长的ISI上没有额外的孤立促进作用，提示ICF延长。