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Abstract: Mammals learn a large repertoire of novel actions by refining variable movements into precise skills. The brain achieves this by assigning credit to movements that led to desired outcomes. Even for simple actions such as reaching to a spatial target, the brain could assign credit to the direction, endpoint target location, speed, etc. As such, different movement strategies may emerge across individuals, depending on what is assigned with credit.My goal is to dissect the sensorimotor areas controlling different aspects of these movements, and probe what determines the learning of different reach strategies.I developed a behavior task in which head-fixed mice generate exploratory forelimb trajectories with a joystick and are rewarded when they hit a covert target in the workspace. As mice learn, they refine their reaches which become less variable in direction, tortuosity, speed, and targeting precision. We show that different aspects of the reach such as direction or speed are learned and controlled through distinct cortical and thalamic networks. For instance, sensorimotor cortex is required to generate reaches with high directional variability across different positions of the workspace, while a specific nucleus of thalamus is required to refine the overall reach direction.
But what reach strategies are mice learning? By relocating the start position in a small number of probe trials I discovered that some animals learned a direction-based strategy (move in the same initial direction from new starts), while others learned an endpoint-based strategy (guide the joystick into the target from new starts, adjusting their direction). Which strategy an individual animal learned correlated with the degree of spatial directional variability during exploration, the aspect of the reach controlled by cortex. We find that when we train reinforcement learning model agents in a similar task they also show this relationship between exploration and endpoint- vs. direction-learning bias. Overall, these findings suggest that the sensorimotor system learns different control strategies by exploring and reinforcing certain movement aspects during learning, and these aspects are likely generated by distinct circuits.
This is an ectopic seminar hosted by the Zebrafish Groupie & is open to the UO community
Abstract: Social behavior ranges from simple pairwise interactions to thousands of individuals coordinating goal-directed movements across animal species. Regardless of the scale, these interactions are governed by multimodal sensory input that requires animals to actively attend to cues and respond appropriately for the context. We leveraged the zebrafish, a highly social and experimentally tractable model organism, to study naturalistic pairwise interactions early in development. We identified stereotyped positions and coordinated movements in interacting pairs, and generated a model to automatically classify states of active interaction. We then manipulated visual and mechanosensory cues to test the contributions of these distinct sensory inputs to behavioral states and corresponding brain activity. Whole-brain immunolabeling for recently active neurons revealed neuronal populations in the forebrain and habenula are selectively active in social contexts and predict sociality of individual pairs. Altogether, we find coordinated social interactions are reliably elicited in juvenile zebrafish early in development, and that specific social behaviors rely on different sensory modalities and distinct brain circuits.
