BioMag Laboratory, HUSLAB, Hospital District of Helsinki and Uusimaa, Helsinki, Finland.
Exp Brain Res. 2012 Aug;220(3-4):223-30. doi: 10.1007/s00221-012-3131-7. Epub 2012 May 29.
A single-pulse transcranial magnetic stimulus (TMS) may induce contraction in many muscles of the body at the same time. This is specially the case when using the double-cone coil to obtain the motor evoked potentials in leg muscles. Even if intensity is kept below threshold for the soleus muscle, TMS induces facilitation of the soleus H reflex that is separated into two phases: the first, peaking at 10-20 ms and the second, peaking at 70-90 ms. We investigated the possibility that TMS-induced facilitation of the H reflex was related, at least in part, to the reafferentation volley reaching the alpha motoneuron after synchronized contraction of other muscles in the body. To test this hypothesis, we examined the effects of vibration on the TMS-induced facilitation of the soleus H reflex. As expected, vibration applied over the triceps tendon caused a significant reduction in H reflex amplitude: 42.4 ± 6.4 % of control values. When conditioned by TMS at intervals corresponding to the first phase, the H reflex was facilitated to the same extent in both conditions: with and without vibration. However, at intervals corresponding to the second facilitation phase, there was a significantly reduced facilitation with vibration. These differential effects of vibration on the two phases of the TMS-induced facilitation of the H reflex indicate a different mechanism for each facilitation phase. The first phase could result from direct corticospinal excitatory input, while the second phase might depend on inputs via Ia afferents from heteronymous muscles.
单次经颅磁刺激（TMS）可能会同时引起身体许多肌肉收缩。当使用双锥线圈获得腿部肌肉的运动诱发电位时，尤其如此。即使强度保持在比目鱼肌的阈下水平，TMS 也会引起比目鱼肌 H 反射的易化，该反射分为两个阶段：第一阶段，在 10-20ms 时达到峰值，第二阶段，在 70-90ms 时达到峰值。我们研究了 TMS 诱导的 H 反射易化是否至少部分与再传入冲动到达 alpha 运动神经元有关，这些再传入冲动是在身体其他肌肉同步收缩后到达 alpha 运动神经元的。为了验证这一假设，我们检查了振动对 TMS 诱导的比目鱼肌 H 反射易化的影响。正如预期的那样，在三头肌腱上施加振动会导致 H 反射幅度显著降低：对照值的 42.4±6.4%。当以与第一相期间隔对应的 TMS 进行条件处理时，H 反射在两种情况下都得到了相同程度的易化：有振动和无振动。然而，在与第二相易化间隔对应的情况下，振动会显著降低易化程度。振动对 TMS 诱导的 H 反射易化的两个阶段的这种不同影响表明每个易化阶段的机制不同。第一阶段可能来自直接皮质脊髓兴奋性输入，而第二阶段可能取决于来自异侧肌肉的 Ia 传入的输入。
