Ito Sho, Gomi Hiroaki
NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation, Atsugi, Japan.
School of Engineering, Tokyo Institute of Technology, Yokohama, Japan.
Front Hum Neurosci. 2024 Feb 14;18:1336629. doi: 10.3389/fnhum.2024.1336629. eCollection 2024.
Various functional modulations of the stretch reflex help to stabilize actions, but the computational mechanism behind its context-dependent tuning remains unclear. While many studies have demonstrated that motor contexts associated with the task goal cause functional modulation of the stretch reflex of upper limbs, it is not well understood how visual contexts independent of the task requirements affect the stretch reflex. To explore this issue, we conducted two experiments testing 20 healthy human participants (age range 20-45, average 31.3 ± 9.0), in which visual contexts were manipulated in a visually guided reaching task. During wrist flexion movements toward a visual target, a mechanical load was applied to the wrist joint to evoke stretch reflex of wrist flexor muscle (flexor carpi radialis). The first experiment ( = 10) examined the effect of altering the visuomotor transformation on the stretch reflex that was evaluated with surface electromyogram. We found that the amplitude of the stretch reflex decreased ( = 0.024) when a rotational transformation of 90° was introduced between the hand movement and the visual cursor, whereas the amplitude did not significantly change ( = 0.26) when the rotational transformation was accompanied by a head rotation so that the configuration of visual feedback was maintained in visual coordinates. The results suggest that the stretch reflex was regulated depending on whether the visuomotor mapping had already been acquired or not. In the second experiment ( = 10), we examined how uncertainty in the visual target or hand cursor affects the stretch reflex by removing these visual stimuli. We found that the reflex amplitude was reduced by the disappearance of the hand cursor ( = 0.039), but was not affected by removal of the visual target ( = 0.27), suggesting that the visual state of the body and target contribute differently to the reflex tuning. These findings support the idea that visual updating of the body state is crucial for regulation of quick motor control driven by proprioceptive signals.
牵张反射的各种功能调节有助于稳定动作，但其上下文依赖调谐背后的计算机制仍不清楚。虽然许多研究表明，与任务目标相关的运动上下文会导致上肢牵张反射的功能调节，但对于独立于任务要求的视觉上下文如何影响牵张反射，人们还了解得不够透彻。为了探究这个问题，我们进行了两项实验，测试了20名健康人类参与者（年龄范围20 - 45岁，平均31.3 ± 9.0），在一项视觉引导的伸手任务中对视觉上下文进行了操控。在向视觉目标进行腕关节屈曲运动时，对手腕关节施加机械负荷以诱发腕屈肌（桡侧腕屈肌）的牵张反射。第一个实验（n = 10）研究了改变视觉运动转换对通过表面肌电图评估的牵张反射的影响。我们发现，当手部运动和视觉光标之间引入90°的旋转变换时，牵张反射的幅度降低（p = 0.024），而当旋转变换伴随着头部旋转，从而在视觉坐标中保持视觉反馈的配置时，幅度没有显著变化（p = 0.26）。结果表明，牵张反射是根据视觉运动映射是否已经习得而受到调节的。在第二个实验（n = 10）中，我们通过去除这些视觉刺激来研究视觉目标或手部光标中的不确定性如何影响牵张反射。我们发现手部光标的消失会降低反射幅度（p = 0.039），但去除视觉目标则不会影响反射幅度（p = 0.27），这表明身体和目标的视觉状态对反射调谐的贡献不同。这些发现支持了这样一种观点，即身体状态的视觉更新对于由本体感觉信号驱动的快速运动控制的调节至关重要。
