A brainstem module for backward locomotion reveals direction-selective premotor circuits

Smooth locomotion requires precise directional control, yet the neural circuits governing navigational transitions remain elusive. Here, we identify the pontine backward locomotion center (PBLC) as a key brainstem node for backward locomotion in mice. PBLC glutamatergic neurons are preferentially recruited during backward locomotion; their activation elicits robust backward walking with naturalistic gait features, whereas their inhibition suppresses backward movement across multiple behavioral contexts. PBLC neurons send ascending projections to the peri-fasciculus retroflexus and descending projections to the paramedian reticular nucleus (PMn). Activating spinal-projecting PMn glutamatergic neurons evokes backward locomotion, whereas PMn ablation suppresses PBLC-evoked backward movement. The PBLC lies within an anteroposteriorly organized set of brainstem regions that includes the cuneiform nucleus, ventral laterodorsal tegmental nucleus, and lateral parabrachial nucleus, associated with forward locomotion, ipsilateral turning, and locomotor arrest, respectively. Together, these findings define a supraspinal circuit for backward locomotion and reveal neighboring brainstem modules associated with distinct locomotor actions.