UNCOVERING PRINCIPLES IN BRAINSTEM PROCESSING OF SPATIAL AND DIRECTIONAL CUES FROM SENSORS ACROSS THE BODY TO MOTOR COMMANDS

Animals navigate by transforming distributed sensory inputs into discrete motor actions, yet how stimulus features such as intensity, frequency, and duration are integrated with spatial information to bias action selection remains poorly understood. A major challenge in vertebrate species has been finding emerging principles of how graded sensory signals are converted into categorical motor commands in the brainstem. The lateral line (LL) system of zebrafish constitutes an ideal model to investigate principles in the brainstem underlying the integration of sensory inputs across the body. With responses to directionality across virtually all LL sensors along the larval zebrafish, we uncovered that processing occurs via a simple egocentric framework, in which spatial and directional flow cues converge onto functionally distinct motor command pathways. Building on this foundation, we now ask how variation in stimulus strength and temporal structure shapes the recruitment of sensory interneurons and downstream motor command circuits to determine behavioral output. The LL links peripheral sensors to reticulospinal neurons through only a few synapses, offering a unique opportunity to follow the transformation from stimulus to action at cellular resolution. By systematically varying stimulus direction, intensity, frequency, and duration at each sensor position, we determine how key parameters are encoded within the brainstem to bias the selection of forward locomotion, avoidance turns, and approach behaviors. By systematically varying both the sensor position and temporal or intensity structure of sensory inputs, this work reveals how vertebrate sensorimotor circuits route multidimensional signals along distinct motor command pathways that bias action selection.