Redefining the central pattern generator for vertebrate locomotion.

Since its original formulation, the concept of the central pattern generator (CPG) has provided a foundational framework for understanding vertebrate locomotion. Recent advances in circuit-level neuroscience in zebrafish have redefined the CPG as a dynamic, modular and hybrid sensorimotor system. A central shift has been the replacement of the classical view of the CPG as a unitary rhythm generator with the idea that it is made up of speed-specific modules that are recruited via gear-shifting mechanisms tailored to behavioural demands. Brainstem circuits have emerged as layered controllers that initiate locomotion and modulate episode duration, speed and direction, whereas motor neurons and proprioceptors are now recognized as integral CPG components that shape rhythm and coordination. Here, I use zebrafish as a primary reference point — alongside explicit comparisons to conserved and divergent principles in mammals — to highlight new facets of the vertebrate CPG that redefine it as a highly adaptable, multilayered control system that is continuously tuned by sensory feedback and descending input. This offers a roadmap for decoding the neural logic of adaptive movement across contexts and evolutionary scales and highlights how principles revealed in zebrafish can provide testable hypotheses for terrestrial vertebrates. The neuronal circuits that comprise the spinal cord central pattern generator (CPG) orchestrate the rhythmic and coordinated motor activity that underlies locomotion. El Manira describes recent advances in our understanding of the organization and operation of the CPG, highlighting findings that have revealed its distributed, modular and adaptable nature.