RT Journal Article SR Electronic T1 Hippocampal Pattern Separation Supports Reinforcement Learning JF bioRxiv FD Cold Spring Harbor Laboratory SP 293332 DO 10.1101/293332 A1 Ian Ballard A1 Anthony D. Wagner A1 Samuel M. McClure YR 2018 UL http://biorxiv.org/content/early/2018/09/20/293332.abstract AB Animals rely on learned associations to make decisions. Associations can be based on relationships between object features (e.g., the three-leaflets of poison ivy leaves) and outcomes (e.g., rash). More often, outcomes are linked to multidimensional states (e.g., poison ivy is green in summer but red in spring). Feature-based reinforcement learning fails when the values of individual features depend on the other features present. One solution is to assign value to multifeatural conjunctive representations. We tested if the hippocampus formed separable conjunctive representations that enabled learning of response contingencies for stimuli of the form: AB+, B-, AC-, C+. Pattern analyses on functional MRI data showed the hippocampus formed conjunctive representations that were dissociable from feature components and that these representations influenced striatal PEs. Our results establish a novel role for hippocampal pattern separation and conjunctive representation in reinforcement learning.