Control of stepping velocity in a single insect leg during walking

Abstract

In the single middle leg preparation of the stick insect walking on a treadmill, the activity of flexor and extensor tibiae motor neurons and muscles, which are responsible for the movement of the tibia in stance and swing phases, respectively, was investigated with respect to changes in stepping velocity. Changes in stepping velocity were correlated with cycle period. There was a close correlation of flexor motor neuron activity (stance phase) with stepping velocity, but the duration and activation of extensor motor neurons (swing phase) was not altered. The depolarization of flexor motor neurons showed two components. At all step velocities, a stereotypic initial depolarization was generated at the beginning of stance phase activity. A subsequent larger depolarization and activation was tightly linked to belt velocity, i.e. it occurred earlier and with larger amplitude during fast steps compared with slow steps. Alterations in a tonic background excitation appear not to play a role in controlling the motor neuron activity for changes in stepping velocity. Our results indicate that in the single insect leg during walking, mechanisms for altering stepping velocity become effective only during an already ongoing stance phase motor output. We discuss the putative mechanisms involved.

Activity Patterns and Timing of Muscle Activity in the Forward Walking and Backward Walking Stick InsectCarausius morosus

“…This has been long known for stick insects walking forward on nonslippery substrates (Graham 1972(Graham , 1985Wendler 1964), although it was unclear whether this relationship held for forward walks on a slippery surface or for backward walks. Our findings confirm previous results (Büschges et al 1995;Gabriel and Büschges 2007;Gruhn et al 2009b) showing that in pharmacologically activated neuron preparations only stance motor neuron firing duration, and in single leg preparations only leg stance duration, vary with cycle period. We have not tested whether the time of onset of muscle bursting changes with the rate of walking.…”

“…Many studies on stick insect walking have been conducted in preparations with reduced leg number (e.g., Akay et al 2001Akay et al , 2004Fischer et al 2001;Gabriel and Büschges 2007;Gabriel et al 2003;von Uckermann and Büschges 2009). Because these preparations lack interleg sensory interactions, it is important to test whether data from such experiments are applicable to intact animals.…”

Cues for acoustic detection of prey: insect rustling sounds and the influence of walking substrate

“…A fast-walking insect will produce more footsteps per unit time than a slowly walking one (Wendler, 1964;Graham, 1972;Gabriel and Bueschges, 2007). Therefore, more foot-substrate and also more body-substrate contacts and hence more clicks per unit time will result.…”

“…Furthermore, the predator needs to account for the insect's walking speed when evaluating the amplitude cues. This is easily conceivable, as speed is coded in steps per unit time (Gabriel and Bueschges, 2007) and these will translate into click rate. Finally, the predator must also know the prey's distance to estimate the source amplitude from the received amplitude.…”

Walking: technology and biology

“…Humans belong to the mammals, and mammals possess much more complex control behaviour than insects, which are easier to investigate and where as a consequence quite a lot about walking and walking control is known. Cruse et al (2006), Gabriel & Büschges (2006) and their research groups are working on the problems of walking and walking control of stick insects. The control concept of these insects is widely decentralized including more or less three layers, the lowest layers for stabilization purposes, the middle layer in a similar form as a finite state machine for controlling the cycles and regarding all unexpected obstacles and the upper layer for organizing the gaits by influencing neighbouring legs shifting their phase in the right direction, inhibiting some actions or set actions going.…”