Laboratory of Applied Biology, Research Unit in Applied Neurophysiology, ULB-Neurosciences Institute (UNI), Faculty for Motor Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium.
J Physiol. 2021 Mar;599(5):1551-1566. doi: 10.1113/JP281093. Epub 2021 Feb 2.
Changes in corticospinal excitability prior to a contraction may depend on its characteristics, including the rate of torque development. This study compared the specific modulation of cortical and spinal excitability during the preparation phase (last 500 ms before contraction) of fast (ballistic) and ramp contractions of ankle dorsiflexors, using transcranial magnetic stimulation and peripheral nerve stimulation. The results indicate earlier changes at the cortical than at the spinal level during the preparation phase of both contraction types. However, these adjustments are delayed prior to ballistic relative to ramp contractions. This study suggests that the time course of change in cortical and spinal excitability during the preparation phase of a voluntary action is specific to the intended rate of torque development of the upcoming contraction.
The present study investigated cortical and spinal excitability during the preparation phase of ballistic (BAL) and ramp (RAMP) isometric contractions. To this end, young adults performed BAL and RAMP (1500 ms torque rise time) contractions, reaching a similar torque level, with the ankle dorsiflexor muscles. Transcranial magnetic stimulation of the motor cortex was randomly applied to record motor evoked potentials (MEP) in the tibialis anterior during the last 500 ms preceding the contraction (n = 16). Short-interval intracortical inhibition (SICI; n = 10) and spinal motor neurone excitability (F-wave occurrence; n = 8) were also assessed during this period. Data were averaged over 100 ms time windows beginning 500 ms prior to the onset of contractions. An increase in MEP amplitude and a decrease in SICI were observed from the 200-100 ms and 300-200 ms time windows prior to BAL and RAMP contractions (P < 0.05), respectively, with greater changes prior to RAMP than to BAL within the 300-200 ms time window (P < 0.05). F-wave occurrence, used to assess spinal motor neurone excitability, increased prior to RAMP (200-100 ms, P < 0.05) but not BAL contractions. Data obtained in a few participants during the last 100 ms confirmed a delayed and steeper rise in corticospinal excitability prior to BAL contractions. These results indicate earlier changes at the cortical than at the spinal level, with delayed changes prior to BAL contractions. This study suggests that the time course of change in cortical and spinal excitability during the preparation phase of a voluntary action is specific to the intended rate of torque development of the upcoming contraction.
在收缩前，皮质脊髓兴奋性的变化可能取决于收缩的特征，包括力矩发展的速度。本研究使用经颅磁刺激和外周神经刺激，比较了快速（弹道）和斜坡踝关节背屈肌收缩准备阶段（收缩前 500ms）皮质和脊髓兴奋性的特定调制。结果表明，在两种收缩类型的准备阶段，皮质兴奋性的变化早于脊髓水平。然而，与斜坡收缩相比，弹道收缩前的这些调整会延迟。本研究表明，在自愿动作的准备阶段，皮质和脊髓兴奋性变化的时间过程与即将到来的收缩的预期力矩发展速度有关。
本研究调查了弹道（BAL）和斜坡（RAMP）等速收缩准备阶段的皮质和脊髓兴奋性。为此，年轻成年人用踝关节背屈肌进行 BAL 和 RAMP（1500ms 转矩上升时间）收缩，达到相似的转矩水平。在收缩前的最后 500ms 内，经颅磁刺激运动皮层，记录胫骨前肌的运动诱发电位（MEP）（n=16）。在此期间还评估了短程抑制（SICI；n=10）和脊髓运动神经元兴奋性（F 波出现；n=8）。数据在收缩前 500ms 开始的 100ms 时间窗口中平均。与 BAL 和 RAMP 收缩相比，从 200-100ms 和 300-200ms 时间窗口观察到 MEP 幅度增加和 SICI 减少（P<0.05），在 300-200ms 时间窗口内，RAMP 比 BAL 变化更大（P<0.05）。用于评估脊髓运动神经元兴奋性的 F 波出现，在 RAMP（200-100ms，P<0.05）但不是 BAL 收缩前增加。在最后 100ms 期间，少数参与者获得的数据证实了 BAL 收缩前皮质脊髓兴奋性的延迟和陡峭上升。这些结果表明，在准备阶段，皮质兴奋性的变化早于脊髓水平，而 BAL 收缩前的变化延迟。本研究表明，在自愿动作的准备阶段，皮质和脊髓兴奋性变化的时间过程与即将到来的收缩的预期力矩发展速度有关。
