Control of Turning Behaviors by Spinal Projection Neurons in the Larval Zebrafish

The precise ways in which the brain communicates with the spinal cord to generate selective motor output is little understood. We focus on a small group of spinal projection neurons (SPNs), which are known to play a necessary role in controlling turning behaviors in zebrafish. Here, we show that these neurons serve to bias the direction, amplitude and frequency of the first tail deflection of a swim bout, while the remainder of the swim remains unaffected and symmetrical. Furthermore, we find that the size of the turning angle correlates strongly with the graded activity of a subset of these neurons. Simulation studies support the notion that the target of these SPNs is a subset of commissural inhibitory spinal interneurons. Our findings show that the brainstem can control a switch in behavior, such as transforming forward swims into turns, by the graded activity of a small set of dedicated SPNs.