Animal behaviors are complex and hierarchical spatiotemporal patterns. In the popular model organism Caenorhabditis elegans, behavioral sequences on a slower timescale emerge from ordered and flexible transitions between different motor states, such as forward movement, reversal, and turn. On a faster timescale, intricate head movements break down into distinct dynamic modes, including the one that initiates coherent bending waves, propelling the animal to move forward.
The fast and slow dynamics are underpinned by different layers of the neural circuitry: low-level motor circuits, including central pattern generators, drive the fast dynamics, whereas the slower ones emerge from the recurrent interactions among high-level interneurons, integral to behavioral decision-making processes. By bringing together quantitative behavioral analysis, calcium imaging, and genetic approaches, I will present functional circuit motifs and computational algorithms that dictate slow and fast motor sequences. Special emphasis will be placed on a pair of interneurons that uniquely shape both fast and slow dynamics, underscoring their dual role in motor control. Finally, I will explore and speculate the principles by which the neural circuit as a whole orchestrates hierarchical behavioral patterns.