Analysis of a network model for inter-leg coordination in multi-legged locomotion
Final Report Abstract
In the research on terrestrial locomotion it is of fundamental importance to understand the neural control of the movements of individual legs and the coordination between the different legs. This problem can be studied in insects (e.g. the stick insect) much more easily than in vertebrates. Results from insects indicate the existence of weak neural connections between the rhythm generating units (CPGs), which periodically drive the individual legs. These connections are enhanced by local sensory feedback signals, like mechanical load signals from the legs. They are crucial for the coordination of the movements of the individual legs. In the past, my group and I had constructed mathematical models using some of these results and principles. Starting from these models we set out to answer specific questions on the neural processes that underlie the coordination between segmental CPGs in multi-legged animals during locomotion. (1) We found that neural circuits between CPGs are coupled in a ring-like structure with no cross-connections being present. In addition, a long-range modulatory influence from the hind leg to the CPG driving the front leg was discovered. We further emphasized that excitatory connections play a more important role in interleg coordination than inhibitory ones. (2) We found that proprioceptive feedback affects motor patterns in a very specific way. Decoupling of the front or the hind leg from the locomotor system and thereby the missing sensory feedback from these legs, did - in contrast to the decoupling of the middle legs - not lead to the disruption of coordinated locomotion of the remaining legs. Our model suggests possible mechanisms that might underlie these changes if a leg is lost or if a front leg is decoupled from the rest of the locomotor system due to the performance of a search movement. (3) We developed a six‐leg model of stick‐insect walking. Our main goal was to prove that the same model can mimic a variety of walking‐related behavioral modes, as well as the most common coordination patterns of walking just by changing the values of a few input or internal variables. As a result, the model can reproduce the basic coordination patterns of walking: tetrapod and tripod and the transition between them as walking speed changes. It can also mimic stop and restart, change from forward‐to‐backward walking and back. Finally, it can exhibit search movements of the front legs both while walking or standing still. The mechanisms of the model that enable it to produce the aforementioned behavioral modes can hint at and prove helpful in uncovering further details of the biological mechanisms underlying walking. Last, but not least, we showed that our detailed network model as well as its phase-reduced version are generalizable to other insect types and animals with more than 6 legs.
Publications
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2015. A network model comprising 4 segmental, interconnected ganglia, and its application to simulate multilegged locomotion in crustaceans, Journal of Computational Neuroscience, 38(3),601-16
Grabowska, M., Toth, T.I., Smarandache-Wellmann, C., Daun-Gruhn, S.
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2015. Investigating inter-segmental connections between thoracic ganglia in the stick insect by means of experimental and simulated phase response curves. Biological Cybernetics, 109(3), 349-362
Toth, T.I., Grabowska, M., Rosjat, N., Hellekes, K., Borgmann, A., Daun-Gruhn, S.
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2016. A three-leg model producing tetrapod and tripod coordination patterns of ipsilateral legs in the stick insect, Journal of Neurophysiology, 115(2), 887-906
Toth, T.I., Daun-Gruhn, S.
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2017. Effects of functional decoupling of a leg in a model of stick insect walking incorporating three ispilateral legs. Physiological Reports, 5(4), e13154
Toth, T., Daun, S.
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2017. Intra- and intersegmental influences among central pattern generating networks in the walking system of the stick insect. Journal of Neurophysiology, 118(4), 2296-2310
Mantziaris, C., Bockemühl, T., Holmes, P., Borgmann, A., Daun, S., Büschges, A.
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2017. Modeling search movements of an insect's front leg. Physiological Reports, 5(22), e13489
Toth, T.I., Berg, E., Daun, S.
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2018. The role of phase shifts of sensory inputs in walking revealed by means of phase reduction. Journal of Computational Neuroscience, 44(1), 313-339
Yeldesbay, A., Toth, T.I., Daun, S.
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2019. A kinematic model of stick-insect walking. Physiological Reports, 7(8): e14080
Toth, T.I., Daun, S.
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2019. Unravelling intra- and intersegmental neuronal connectivity between central pattern generating networks in a multi-legged locomotor system. PLoS One, 14(8):e0220767
Daun, S., Mantziaris, C., Toth, T.I., Büschges, A., Rosjat, N.
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2020. Intra- and intersegmental neural network architectures determining rhythmic motor activity in insect locomotion, Communications in Nonlinear Science and Numerical Simulation, 82, March, 105078
Yeldesbay, A., Daun, S.
