Theunissen Leslie M, Dürr Volker
Department of Biological Cybernetics, Bielefeld University, Bielefeld, Germany ; Cognitive Interaction Technology - Center of Excellence, Bielefeld University, Bielefeld, Germany.
PLoS One. 2013 Dec 23;8(12):e85321. doi: 10.1371/journal.pone.0085321. eCollection 2013.
Adaptive, context-dependent control of locomotion requires modulation of centrally generated rhythmic motor patterns through peripheral control loops and postural reflexes. Thus assuming that the modulation of rhythmic motor patterns accounts for much of the behavioural variability observed in legged locomotion, investigating behavioural variability is a key to the understanding of context-dependent control mechanisms in locomotion. To date, the variability of unrestrained locomotion is poorly understood, and virtually nothing is known about the features that characterise the natural statistics of legged locomotion. In this study, we quantify the natural variability of hexapedal walking and climbing in insects, drawing from a database of several thousand steps recorded over two hours of walking time.
We show that the range of step length used by unrestrained climbing stick insects is large, showing that step length can be changed substantially for adaptive locomotion. Step length distributions were always bimodal, irrespective of leg type and walking condition, suggesting the presence of two distinct classes of steps: short and long steps. Probability density of step length was well-described by a gamma distribution for short steps, and a logistic distribution for long steps. Major coefficients of these distributions remained largely unaffected by walking conditions. Short and long steps differed concerning their spatial occurrence on the walking substrate, their timing within the step sequence, and their prevalent swing direction. Finally, ablation of structures that serve to improve foothold increased the ratio of short to long steps, indicating a corrective function of short steps.
Statistical and functional differences suggest that short and long steps are physiologically distinct classes of leg movements that likely reflect distinct control mechanisms at work.
适应性的、依赖于环境的运动控制需要通过外周控制回路和姿势反射来调节中枢产生的节律性运动模式。因此，假设节律性运动模式的调节是腿部运动中观察到的大部分行为变异性的原因，那么研究行为变异性是理解运动中依赖于环境的控制机制的关键。迄今为止，对无约束运动的变异性了解甚少，对于表征腿部运动自然统计学特征的特性几乎一无所知。在本研究中，我们从记录了两个小时行走时间的数千步数据库中，对昆虫六足行走和攀爬的自然变异性进行了量化。
我们表明，无约束的攀爬竹节虫所使用的步长范围很大，这表明步长可以为了适应性运动而大幅改变。步长分布始终是双峰的，与腿的类型和行走条件无关，这表明存在两种不同类型的步：短步和长步。短步的步长概率密度可以用伽马分布很好地描述，长步的步长概率密度可以用逻辑分布很好地描述。这些分布的主要系数在很大程度上不受行走条件的影响。短步和长步在行走底物上的空间出现位置、在步序列中的时间以及它们普遍的摆动方向方面存在差异。最后，切除用于改善立足点的结构会增加短步与长步的比例，这表明短步具有校正功能。
统计和功能上的差异表明，短步和长步是生理上不同类型的腿部运动，可能反映了不同的控制机制在起作用。
