Suppression of Ventral Hippocampal Output Impairs Integrated Orbitofrontal Encoding of Task Structure

The hippocampus and orbitofrontal cortex (OFC) both make important contributions to decision making and other cognitive processes. However, despite anatomical links between the two, few studies have tested the importance of hippocampal-OFC interactions. Here, we recorded OFC neurons in rats performing a decision making task while suppressing activity in a key hippocampal output region, the ventral subiculum. OFC neurons encoded information about expected outcomes and rats' responses. With hippocampal output suppressed, rats were slower to adapt to changes in reward contingency, and OFC encoding of response information was strongly attenuated. In addition, ventral subiculum inactivation prevented OFC neurons from integrating information about features of outcomes to form holistic representations of the outcomes available in specific trial blocks. These data suggest that the hippocampus contributes to OFC encoding of both concrete, low-level features of expected outcomes, and abstract, inferred properties of the structure of the world, such as task state.