Abstract
Multiple mechanisms contribute to the generation, propagation, and coordination of the rhythmic patterns necessary for locomotion in Caenorhabditis elegans. Current experiments have focused on two possibilities: pacemaker neurons and stretch-receptor feedback. Here, we focus on whether it is possible that a chain of multiple network rhythmic pattern generators in the ventral nerve cord also contribute to locomotion. We use a simulation model to search for parameters of the anatomically constrained ventral nerve cord circuit that, when embodied and situated, can drive forward locomotion on agar, in the absence of pacemaker neurons or stretch-receptor feedback. Systematic exploration of the space of possible solutions reveals that there are multiple configurations that result in locomotion that is consistent with certain aspects of the kinematics of worm locomotion on agar. Analysis of the best solutions reveals that gap junctions between different classes of motorneurons in the ventral nerve cord can play key roles in coordinating the multiple rhythmic pattern generators.
Highlights
Understanding how behavior is generated through the interaction between an organism’s brain, its body, and its environment is one of the biggest challenges in neuroscience (Chiel and Beer, 1997; Chiel et al, 2009; Krakauer et al, 2017)
As the parameters for the physiological properties of neurons and synapses involved in forward locomotion in C. elegans are largely unknown, we used an evolutionary algorithm to search through the space of parameters for different configurations that could produce forward movement on agar in the absence of stretch-receptors or pacemaker neurons
Once the isolated neural units could produce rhythmic patterns, they were integrated into the complete neuromechanical model and evolved to move forward in agar using a combined fitness function F1 · F2 (Figure 2B)
Summary
Understanding how behavior is generated through the interaction between an organism’s brain, its body, and its environment is one of the biggest challenges in neuroscience (Chiel and Beer, 1997; Chiel et al, 2009; Krakauer et al, 2017). Understanding locomotion is critical because it is one of the main ways that organisms use to interact with their environments. Locomotion represents a quintessential example of how behavior requires the coordination of neural, mechanical, and environmental forces. Despite the available anatomical knowledge, how the rhythmic patterns are generated and propagated along the body to produce locomotion is not yet fully understood (Cohen and Sanders, 2014; Gjorgjieva et al, 2014; Zhen and Samuel, 2015).
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