C. elegans locomotion: small circuits, complex functions

•The Caenorhabditis elegans motor circuit has a nearly complete connectome.•Neurogenetic studies are unveiling a rich and complex set of signaling relationships between interneurons, motor neurons, and muscle cells.•Progress in electrophysiology, imaging, and optogenetics is leading to a quantitative analysis of dynamical relationships between motor circuit components.

With 302 neurons in the adult Caenorhabditis elegans nervous system, it should be possible to build models of complex behaviors spanning sensory input to motor output. The logic of the motor circuit is an essential component of such models. Advances in physiological, anatomical, and neurogenetic analysis are revealing a surprisingly complex signaling network in the worm's small motor circuit. We are progressing towards a systems level dissection of the network of premotor interneurons, motor neurons, and muscle cells that move the animal forward and backward in its environment.