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Silvia Daun-Gruhn

A neuro-mechanical model of forward, backward and sideward stepping

Silvia Daun-Gruhn1, Sascha Knops1, Tibor Istvan Toth1

1 Department of Animal Physiology, University of Cologne, Cologne, Germany

The mechanism underlying the generation of stepping has been the object of intensive studies. Stepping involves the coordinated movement of different leg joints and is, in the case of insects, produced by antagonistic muscle pairs. In the stick insect, the coordinated actions of three such antagonistic muscle pairs produce leg movements and determine the stepping pattern of the limb. The activity of the muscles is controlled by the nervous system as a whole and more specifically by local neuronal networks for each muscle pair. While many basic properties of these control mechanisms have been uncovered, some important details of their interactions in various physiological conditions have so far remained unknown.

We have created a neuro-mechanical model of the coupled three joint control system of the stick insect’s middle leg to unravel details of the neuronal and mechanical mechanisms driving a stepping single leg in situations other than forward walking [1,2]. The model can generate forward, backward, or sideward stepping. Using the model, it is, because of it's detailed biological description, possible to make detailed suggestions as to how rhythmic stepping might be generated by the central pattern generators of the local neuronal networks, how this activity might be transmitted to the corresponding motoneurons, and how the latter might control the activity of the related muscles. The entirety of these processes yields the coordinated interaction between neuronal and mechanical parts of the system. Moreover, based on experimental findings which state that only the activity of the muscles which move the leg forward and backward is reversed during backwards walking, we hypothesize a mechanism by which motoneuron activity could be modified by a premotor network and suggest that this mechanism might serve as a basis for fast adaptive behaviour, like switches between forward and backward stepping, which occur, for example, during curve walking, and especially sharp turning, of insects.

Acknowledgements

This work was supported by the DFG grant to S. Daun-Gruhn (DA1182/1-1).

References

1. Toth TI, Knops S, Daun-Gruhn S: A neuromechanical model explaining forward and backward stepping in the stick insect. J Neurophysiol 2012, 107(12):3267-80.

2. Knops S, Toth TI, Daun-Gruhn S: A neuromechanical model for the neuronal basis of curve walking in the stick insect. J Neurophysiol 2012, 109(3):679-91.