Matheson Tom, Dürr Volker
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
J Exp Biol. 2003 Sep;206(Pt 18):3175-86. doi: 10.1242/jeb.00534.
The task of a multi-jointed limb making an aimed movement towards a target requires that the movement is regulated against external perturbations such as changing load. In particular, loading one part of a limb leads to altered static forces on all proximal segments, and to additional dynamic joint interaction forces when the limb moves. We have addressed the question of load compensation in an insect preparation in which a locust makes aimed scratching movements with a hind leg in response to tactile stimulation of a wing. We show that loading the femur or tibia with the equivalent of 8.5 times the mass of the tibia (corresponding to an increase of up to 11.6 times the rotational moment of inertia at the femur-tibia joint) does not impair the animal's ability to make well-coordinated, aimed movements of that leg towards different targets. The kinematics of the movements are the same, and animals aim the same part of their distal tibia at the target, regardless of loading. The movements are carried out with equal accuracy and at the same initial velocity under all load conditions. Because loading of the leg does not change the behavioural performance, there is no indication of a change in aiming strategy. This implies high leg joint stiffness and/or the existence of high gain proprioceptive control loops. We have previously shown that in the unloaded condition, movements elicited by stimuli to different places on the wing are driven by a single underlying movement pattern that shifts depending on stimulus location along the wing surface. Our present data show that leg proprioceptive inputs are also integrated into the leg motor networks, rendering hind limb targeting robust against large changes in moment of inertia.
多关节肢体朝着目标进行定向运动的任务要求该运动能够抵御外部干扰，如负载变化。特别是，肢体某一部分加载会导致所有近端节段上的静态力发生改变，并且在肢体移动时会产生额外的动态关节相互作用力。我们研究了昆虫实验中的负载补偿问题，在该实验中，蝗虫受到翅膀触觉刺激后用后腿进行定向抓挠运动。我们发现，在股骨或胫骨上加载相当于胫骨质量8.5倍的重量（相当于股骨 - 胫骨关节处转动惯量增加高达11.6倍），并不会损害动物用该腿向不同目标做出协调良好的定向运动的能力。无论负载如何，运动的运动学特征相同，动物都将胫骨远端的同一部分对准目标。在所有负载条件下，运动都以相同的精度和相同的初始速度进行。由于腿部加载不会改变行为表现，因此没有迹象表明瞄准策略发生了变化。这意味着腿部关节具有高刚度和/或存在高增益本体感受控制回路。我们之前已经表明，在无负载条件下，由翅膀上不同位置的刺激引发的运动是由单一的潜在运动模式驱动的，该模式会根据沿着翅膀表面的刺激位置而移动。我们目前的数据表明，腿部本体感受输入也被整合到腿部运动网络中，使后肢瞄准在转动惯量发生大幅变化时具有鲁棒性。
