Neurons in rat orbitofrontal cortex and medial prefrontal cortex exhibit distinct responses in reward and strategy-update in a risk-based decision-making task

The orbitofrontal cortex (OFC) and the medial prefrontal cortex (mPFC) are known to participate in risk-based decision-making. However, whether neuronal activities of these two brain regions play similar or differential roles during different stages of risk-based decision-making process remains unknown. Here we conducted multi-channel in vivo recordings in the OFC and mPFC simultaneously when rats were performing a gambling task. Rats were trained to update strategy as the task was shifted in two stages. Behavioral testing suggests that rats exhibited different risk preferences and response latencies to food rewards during stage-1 and stage-2. Indeed, the firing patterns and numbers of non-specific neurons and nosepoking-predicting neurons were similar in OFC and mPFC. However, there were no reward-expecting neurons and significantly more reward-excitatory neurons (fired as rats received rewards) in the mPFC. Further analyses suggested that nosepoking-predicting neurons may encode the overall value of reward and strategy, whereas reward-expecting neurons show more intensive firing to a big food reward in the OFC. Nosepoking-predicting neurons in mPFC showed no correlation with decision-making strategy updating, whereas the response of reward-excitatory neurons in mPFC, which were barely observed in OFC, were inhibited during nosepoking, but were enhanced in the post-nosepoking period. These findings indicate that neurons in the OFC and mPFC exhibit distinct responses in decision-making process during reward consumption and strategy updating. Specifically, OFC encodes the overall value of a choice and is thus important for learning and strategy updating, whereas mPFC plays a key role in monitoring and execution of a strategy.