Neuromechanical modelling of C. elegans locomotion: proprioceptive feedback in the ventral nerve cord

The simple undulatory gait of the small nematode worm Caenorhabditis elegans, along with its well characterised nervous system make it an ideal organism for studying the neural control of locomotion. Smooth mechanical propagating waves propel the worm's body through a wide variety of environments as a result of both highly coordinated motor output and finely tuned body mechanics. Inspired by previous modelling efforts, I employ an updated neuromechanical model to identify the effects of neural and mechanical modulation of C. elegans' locomotory gait and explore underlying control mechanisms, with a focus on proprioceptive feedback in the ventral nerve cord. I investigate interactions between body elasticity and fluid viscosity to highlight a fundamental condition for mechanically induced gait modulation, and quantitatively match this modulation with experimental results to predict the worm's material parameters under the model assumptions. By considering characteristics unique to proprioceptive neurons, I show how manifestations of internal gait modulation contrast that of external modulation. Manipulating the strength of various inhibitory connections within the nerve cord suggest that GABAergic connections impact locomotion in qualitatively different ways depending on location. Inhibition at the neuromuscular junctions may be used to control undulation frequency across multiple environments, while asymmetric neural inhibition supports robust high frequency undulations, in line with existing model predictions. Recent experimental work evidences simultaneous, independently driven oscillations with different frequencies along the body when anterior and posterior regions are isolated by external inhibition. By inhibiting anterior muscles in model worms, I find that purely proprioceptive control is capable of qualitatively capturing multiple frequency undulations. In such conditions the effects of neural coupling appear to dominate mechanical coupling, at least during crawling.