Experimental Psychology, Justus Liebig University Giessen, Otto-Behaghel Str. 10F, D-35394 Giessen, Germany.
Experimental Psychology, Justus Liebig University Giessen, Otto-Behaghel Str. 10F, D-35394 Giessen, Germany.
Neuroimage. 2021 Aug 1;236:118000. doi: 10.1016/j.neuroimage.2021.118000. Epub 2021 Apr 14.
Somatosensory signals on a moving limb are typically suppressed. This results mainly from a predictive mechanism that generates an efference copy, and attenuates the predicted sensory consequences of that movement. Sensory feedback is, however, important for movement control. Behavioral studies show that the strength of suppression on a moving limb increases during somatosensory reaching, when reach-relevant somatosensory signals from the target limb can be additionally used to plan and guide the movement, leading to increased reliability of sensorimotor predictions. It is still unknown how this suppression is neurally implemented. In this fMRI study, participants reached to a somatosensory (static finger) or an external target (touch-screen) without vision. To probe suppression, participants detected brief vibrotactile stimuli on their moving finger shortly before reach onset. As expected, sensitivity to probes was reduced during reaching compared to baseline (resting), and this suppression was stronger during somatosensory than external reaching. BOLD activation associated with suppression was also modulated by the reach target: relative to baseline, processing of probes during somatosensory reaching led to distinct BOLD deactivations in somatosensory regions (postcentral gyrus, supramarginal gyrus-SMG) whereas probes during external reaching led to deactivations in the cerebellum. In line with the behavioral results, we also found additional deactivations during somatosensory relative to external reaching in the supplementary motor area, a region linked with sensorimotor prediction. Somatosensory reaching was also linked with increased functional connectivity between the left SMG and the right parietal operculum along with the right anterior insula. We show that somatosensory processing on a moving limb is reduced when additional reach-relevant feedback signals from the target limb contribute to the movement, by down-regulating activation in regions associated with predictive and feedback processing.
运动肢体的体感信号通常会受到抑制。这主要是由于一种预测机制产生了传出副本，并减弱了该运动的预测感觉后果。然而，感觉反馈对于运动控制很重要。行为研究表明，在体感伸手时，运动肢体上的抑制强度会增加，此时可以额外使用来自目标肢体的与伸手相关的体感信号来计划和引导运动，从而提高运动感觉预测的可靠性。目前尚不清楚这种抑制是如何在神经上实现的。在这项 fMRI 研究中，参与者在没有视觉的情况下伸手去够体感（静态手指）或外部目标（触摸屏）。为了探测抑制，参与者在伸手开始前短暂地检测到他们运动手指上的振动触觉刺激。正如预期的那样，与基线（休息）相比，在伸手过程中对探针的敏感性降低，并且这种抑制在体感伸手时比外部伸手时更强。与抑制相关的 BOLD 激活也受到伸手目标的调制：与基线相比，在体感伸手期间处理探针会导致体感区域（中央后回、缘上回-SMG）的 BOLD 去激活，而在外部伸手期间处理探针会导致小脑的去激活。与行为结果一致，我们还发现，在体感相对于外部伸手时，在补充运动区中还存在额外的去激活，该区域与运动感觉预测有关。体感伸手还与左侧 SMG 与右侧顶叶脑岛之间的功能连接增加有关。我们表明，当来自目标肢体的额外与伸手相关的反馈信号有助于运动时，运动肢体上的体感处理会减少，方法是下调与预测和反馈处理相关的区域的激活。
