Neural Control and Modulation of Swimming Speed in the Larval Zebrafish

•Larval zebrafish can adjust their swimming speed to match a visual stimulus•Ablation or activation of the nMLF implicates it in controlling swimming speed•Activity in identified nMLF neurons correlates with specific behavioral parameters•This suggests the nMLF modulates swimming by differentially driving spinal circuits

SummaryVertebrate locomotion at different speeds is driven by descending excitatory connections to central pattern generators in the spinal cord. To investigate how these inputs determine locomotor kinematics, we used whole-field visual motion to drive zebrafish to swim at different speeds. Larvae match the stimulus speed by utilizing more locomotor events, or modifying kinematic parameters such as the duration and speed of swimming bouts, the tail-beat frequency, and the choice of gait. We used laser ablations, electrical stimulation, and activity recordings in descending neurons of the nucleus of the medial longitudinal fasciculus (nMLF) to dissect their contribution to controlling forward movement. We found that the activity of single identified neurons within the nMLF is correlated with locomotor kinematics, and modulates both the duration and oscillation frequency of tail movements. By identifying the contribution of individual supraspinal circuit elements to locomotion kinematics, we build a better understanding of how the brain controls movement.