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Poster C143 in Poster Session C - Friday, August 9, 2024, 11:15 am – 1:15 pm, Johnson Ice Rink
Planning in the Hippocampus: Linking Actions and Outcomes to Guide Behavior
Sarah Jo C Venditto1 (), Kevin J Miller2,3, Nathaniel D Daw1, Carlos D Brody1,4; 1Princeton University, 2Google DeepMind, 3University College London, 4Howard Hughes Medical Institute
Planning requires an internal model of the world that can be flexibly utilized to link actions and subsequent consequences across time and space. The hippocampus, often referred to as a “cognitive map,” is known for encoding the location of an animal within complex environments by representing salient states, both spatial and non-spatial. These representations can extend to non-local states, making them well-suited to support this internal action-outcome model. While the hippocampus has been causally linked to planning in both humans and rodents, how hippocampal representations carry out this function is poorly understood. To address this, we record from dorsal hippocampus while rats perform a multi-step reward-guided task that employs probabilistic transitions between actions and outcomes, the rat two-step task, which has been shown to reliably elicit planning. We find that hippocampal activity encodes the task space and exhibits “splitter cells” that differentiate similar positions based on preceding choice, providing distinct representations for each combination of choice and outcome. In-between trials, we find oscillating representations that encode the visited outcome paired with both possible choices; however, overall choice encoding is biased towards upcoming choices with a model-based dependence on reward and probabilistic transition.
Keywords: planning hippocampus reinforcement learning credit assignment