Left-right alternation of superior colliculus activity with the stepping rhythm

Fluid behavior requires temporal coordination across brain systems that orchestrate movement. A clear example is locomotion, in which left and right turns are not only precisely coordinated with the ongoing stepping rhythm but occur at opposite phases of the stepping cycle. The circuits underlying this coordination remain poorly understood. We discover that neuronal activity in the mouse superior colliculus, a conserved midbrain structure involved in turning behavior, is tightly phase-locked to the stepping rhythm. Notably, neurons selective for left and right turns fire at opposite phases of the stepping cycle. Moreover, this phase opposition is already evident during straight locomotion, before the animal initiates a turn. By aligning the activity of left and right turn neurons to opposite phases of the stepping cycle, the superior colliculus may create alternating windows of opportunity for left and right turns, facilitating the seamless execution of turns during locomotion.