Terekhov Alexander V, Hayward Vincent
Proc Biol Sci. 2015 Sep 7;282(1814). doi: 10.1098/rspb.2015.1661.
A fundamental problem faced by the brain is to estimate whether a touched object is rigidly attached to a ground reference or is movable. A simple solution to this problem would be for the brain to test whether pushing on the object with a limb is accompanied by limb displacement. The mere act of pushing excites large populations of mechanoreceptors, generating a sensory response that is only weakly sensitive to limb displacement if the movements are small, and thus can hardly be used to determine the mobility of the object. In the mechanical world, displacement or deformation of objects frequently co-occurs with microscopic fluctuations associated with the frictional sliding of surfaces in contact or with micro-failures inside an object. In this study,we provide compelling evidence that the brain relies on these microscopic mechanical events to estimate the displacement of the limb in contact with an object, and hence the mobility of the touched object. We show that when pressing with a finger on a stiff surface, fluctuations that resemble the mechanical response of granular solids provoke a sensation of limb displacement. Our findings suggest that when acting on an external object, prior knowledge about the sensory consequences of interacting with the object contributes to proprioception.
大脑面临的一个基本问题是估计被触摸的物体是牢固地附着在地面参考物上还是可移动的。解决这个问题的一个简单方法是让大脑测试用肢体推物体时是否伴随着肢体位移。仅仅是推的动作就会刺激大量的机械感受器，产生一种感觉反应，如果动作很小，这种反应对肢体位移的敏感度很低，因此很难用来确定物体的可移动性。在机械世界中，物体的位移或变形经常与微观波动同时发生，这些波动与接触表面的摩擦滑动或物体内部的微故障有关。在这项研究中，我们提供了令人信服的证据，证明大脑依靠这些微观机械事件来估计与物体接触的肢体的位移，从而估计被触摸物体的可移动性。我们表明，当用手指按压坚硬表面时，类似于颗粒固体机械响应的波动会引发肢体位移的感觉。我们的研究结果表明，当作用于外部物体时，关于与物体相互作用的感觉后果的先验知识有助于本体感觉。
