Background

Compared to conventional transcranial magnetic stimulation (TMS), the triple stimulation technique (TST) strongly decrease the effects of desynchronization of descending discharges and accompanying phase cancellation that follow TMS and offers a more sensitive method to quantify motor evoked potentials (MEPs).

New method

Using the TST, we explored as to whether sub-threshold TMS evokes peripheral motor neuron discharges (MNs). We compared the number of MEPs elicited by TMS and by TST in fifteen healthy participants. We used the subthreshold intensity of 80 % resting motor threshold. To control the TST assessment of the corticospinal tract, we included a peripheral stimulation control condition, which consisted of peripheral stimulation alone, in a subgroup of five volunteers.

Results

Compared to TMS, TST at sub-threshold intensities did not detect significantly more responses unequivocally attributable to the cortical stimulation. In contrast, the peripheral supra-maximal stimuli produced confounding effects in the TST condition that were, in part, indistinguishable from cortical responses.

Comparison with existing methods

At subthreshold TMS intensities, the TST does not detect more discharges of spinal MNs than conventional TMS and, in addition, it is confounded by effects from peripheral stimulation.

Conclusion

The TST can be useful in assessing the integrity of the MN pool and of the corticospinal tract. However, if used at near threshold intensity, the confounding effects of peripheral stimulation need to be considered; for instance, in paired-pulse stimulation paradigms assessing the cortical physiology.

中文翻译：

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外围刺激影响阈下三重刺激技术

背景

与传统的经颅磁刺激（TMS）相比，三重刺激技术（TST）大大降低了TMS产生的降序放电失步和伴随相抵消的影响，并提供了一种更灵敏的方法来量化运动诱发电位（MEP）。

新方法

使用TST，我们探讨了亚阈值TMS是否引起周围运动神经元放电（MNs）。我们比较了15名健康参与者中TMS和TST诱发的MEP数量。我们使用80％静止运动阈值的亚阈值强度。为了控制皮质脊髓束的TST评估，我们在5名志愿者的亚组中纳入了周围刺激控制条件，该条件仅由周围刺激组成。

结果

与TMS相比，低于阈值强度的TST不能明显检测到明显更多归因于皮层刺激的反应。相反，在TST条件下，外周超最大刺激产生混杂效应，其与皮层反应部分不可区分。

与现有方法的比较

在低于阈值的TMS强度下，TST不能检测到比常规TMS更多的脊柱MNs放电，此外，它还受到周围刺激的影响而感到困惑。

结论

TST可用于评估MN池和皮质脊髓束的完整性。但是，如果以接近阈值的强度使用，则应考虑周围刺激的混杂效应。例如，在成对脉冲刺激范例中评估皮层生理。