Figure 3.

Three competing hypotheses for the production of locomotor patterns are distinguished by the presence and location of oscillators and sensory feedback: (a) During forward locomotion, the neck generates rhythmic dorsoventral bends, and physical, neuronal, or sensory feedback mechanisms propagate them along the body. (b) Coupled oscillators along the body generate and propagate rhythmic dorsoventral bends, and sensory feedback modulates the resulting motor patterns. (c) Sensory feedback extending along the body generates and propagates rhythmic dorsoventral bends. The diagrams on the right show the main differences among the hypotheses in the location of muscles (the pink ovals), oscillators (the round blue arrows), and sensory feedback (the purple arrows) along the anterior–posterior axis (the head is to the right). The diagrams on the left demonstrate the approximate location of increased neuromuscular activity (thick arrows for sensory feedback, round arrows for oscillators) along the body of the nematode (the head is to the right; the blue arrow designates the forward direction).