Rohlén Robin, Torell Frida, Dimitriou Michael
Department of Medical and Translational Biology, Umeå University, Umeå, Sweden.
Department of Diagnostics and Intervention, Umeå University, Umeå, Sweden.
Exp Brain Res. 2025 Aug 18;243(9):198. doi: 10.1007/s00221-025-07139-z.
Stretch reflex responses counteract sudden perturbations, and modulation of reflex gains can facilitate voluntary movement. Recent studies suggest movement preparation includes goal-directed tuning of muscle spindles and an equivalent modulation of both short- and long-latency stretch reflex responses (SLR and LLR), as long as the preparatory delay between 'Cue' and 'Go' exceeds 250 ms. The current study aimed to clarify the minimal preparation time required for goal-directed modulation of SLR and LLR responses and to determine how such modulation progressively evolves with extended preparation. We recorded bipolar electromyographic signals of healthy participants to assess reflex responses to mechanical perturbations induced by a robotic manipulandum in the context of a delayed-reach task. Specifically, we examined how multiple preparatory delays (250, 300, 350, 400, 450, and 500 ms) impact the goal-directed modulation of SLR and LLR responses from the loaded or unloaded pectoralis major, anterior deltoid, and posterior deltoid muscles. We found that preparatory delays of 300 ms and 350 ms are sufficient for goal-directed tuning of SLR responses in the posterior deltoid and pectoralis muscles, respectively. Our results also suggest that unloading (i.e., antagonist loading) may facilitate both the earlier emergence and more robust expression of goal-directed SLR tuning. Goal-directed tuning of LLR responses emerged as early as 250 ms of preparation, and such tuning was robust against muscle load conditions, in line with previous findings. We observed no consistent increase in SLR tuning at preparation delays that extended beyond the required minimum, whereas such enhancement was observed at the LLR epoch. These findings clarify the temporal characteristics of goal-directed stretch reflex gains, which likely emerge through the interplay of multiple feedback mechanisms.
牵张反射反应可抵消突然的扰动，反射增益的调节有助于自主运动。最近的研究表明，运动准备包括对肌梭的目标导向性调整以及对短潜伏期和长潜伏期牵张反射反应（SLR和LLR）的同等调节，只要“提示”和“开始”之间的准备延迟超过250毫秒。本研究旨在阐明对SLR和LLR反应进行目标导向性调节所需的最短准备时间，并确定这种调节如何随着准备时间的延长而逐渐演变。我们记录了健康参与者的双极肌电信号，以评估在延迟伸手任务中对机器人操作器引起的机械扰动的反射反应。具体而言，我们研究了多个准备延迟（250、300、350、400、450和500毫秒）如何影响来自加载或未加载的胸大肌、三角肌前束和三角肌后束肌肉的SLR和LLR反应的目标导向性调节。我们发现，300毫秒和350毫秒的准备延迟分别足以对三角肌后束和胸大肌的SLR反应进行目标导向性调整。我们的结果还表明，卸载（即拮抗肌加载）可能有助于目标导向性SLR调整的更早出现和更强烈的表达。LLR反应的目标导向性调整最早在准备250毫秒时出现，并且这种调整对肌肉负荷条件具有较强的抗性，这与之前的研究结果一致。我们观察到，在超过所需最短时间的准备延迟下，SLR调整没有持续增加，而在LLR阶段观察到了这种增强。这些发现阐明了目标导向性牵张反射增益的时间特征，这可能是通过多种反馈机制的相互作用而出现的。
