How C.elegans Generates Coordinated Forward Locomotion

Locomotion is essential for survival:it enables animals to move towards reward or away from danger,and therefore to adapt in the surrounding environment.Rhythmic movement is one of the most common form of movements,ranging from vibrating wings of a flying insect to a beating heart of a mammal.An understanding of how animals generate coordinated rhythmic movement is a main subject in the field of motor control.Rhythmic movement involves neuromuscular dynamics,feedback of sensory inputs and descending signals from higher neural circuitry.In this dissertation,I focused on the basic circuit logic on how C.elegans generates coherent forward locomotion.To this end,I carried out systematic investigations by performing genetic manipulation and all-optical interrogation of the C.elegans motor circuit.B-type motor neurons,which are positioned in the ventral nerve cord and form neuromuscular junctions with body wall muscle cells,are responsible for C.elegans forward locomotion.The command intemeurons AVB project long processes along the ventral nerve cord and form gap junctions with every B-type motor neuron.I discovered that mid-body B-type motor neurons can generate oscillatory activities,constituting distributed CPGs.AVB interneurons can drive B-type motor neurons from stationary to oscillatory activities through electrical inputs.Moreover,CPGs along the worm body are entrained by directional proprioceptive signal between B-type motor neurons,by which coordinated undulatory waves arise.The network structure of C.elegans nervous system is parsimonious:it compresses functions executed by different cell types in higher animals into one.The compressed and conserved functional circuitry of C.elegans provides new insights into general principles of motor control.