Abstract
With 302 neurons and a near complete reconstruction of the neural and muscle anatomy at the cellular level, C. elegans is an ideal candidate organism to study the neuromechanical basis of behavior. Yet, despite the breadth of knowledge about the neurobiology, anatomy and physics of C. elegans, there are still a number of unanswered questions about one of its most basic and fundamental behaviors: forward locomotion. How the rhythmic pattern is generated and propagated along the body is not yet well understood. We report on the development and analysis of a model of forward locomotion that integrates the neuroanatomy, neurophysiology and body mechanics of the worm. Our model is motivated by recent experimental analysis of the structure of the ventral cord circuitry and the effect of local body curvature on nearby motorneurons, as well as by the lack of consideration of the role of the head motorneurons in current models of locomotion. We developed a neuroanatomicallygrounded model of the head and ventral nerve cord subcircuits, using a neural model capable of reproducing the full range of electrophysiology observed in C. elegans neurons. We integrated the neural model with an existing biomechanical model of the worm’s body, with updated musculature and stretch receptors. Unknown parameters were evolved using a evolutionary algorithm to match the speed of the worm on agar. We performed 100 evolutionary runs and consistently found electrophysiological configurations that reproduced realistic control of forward movement. The ensemble of successful solutions reproduced key experimental observations that they were not designed to fit, including the wavelength and frequency of the propagating wave. Analysis of the ensemble revealed that SMD and RMD are sufficient to drive dorsoventral undulations in the head and neck and that short-range posteriorlydirected proprioceptive feedback is sufficient to propagate the wave along the rest of the body.
