Non-action Learning: Saving Action-Associated Cost Serves as a Covert Reward

Medial prefrontal cortex suppresses reward-seeking behavior with risk of punishment by reducing sensitivity to reward

Reward-seeking behavior is frequently associated with risk of punishment. There are two types of punishment: positive punishment, which is defined as addition of an aversive stimulus, and negative punishment, involves the omission of a rewarding outcome. Although the medial prefrontal cortex (mPFC) is important in avoiding punishment, whether it is important for avoiding both positive and negative punishment and how it contributes to such avoidance are not clear. In this study, we trained male mice to perform decision-making tasks under the risks of positive (air-puff stimulus) and negative (reward omission) punishment, and modeled their behavior with reinforcement learning. Following the training, we pharmacologically inhibited the mPFC. We found that pharmacological inactivation of mPFC enhanced the reward-seeking choice under the risk of positive, but not negative, punishment. In reinforcement learning models, this behavioral change was well-explained as an increase in sensitivity to reward, rather than a decrease in the strength of aversion to punishment. Our results suggest that mPFC suppresses reward-seeking behavior by reducing sensitivity to reward under the risk of positive punishment.

Neuronal representations of reward-predicting cues and outcome history with movement in the frontal cortex

Transformation of sensory inputs to goal-directed actions requires estimation of sensory-cue values based on outcome history. We conduct wide-field and two-photon calcium imaging of the mouse neocortex during classical conditioning with two cues with different water-reward probabilities. Although licking movement dominates the area-averaged activity over the whole dorsal neocortex, the dorsomedial frontal cortex (dmFrC) affects other dorsal frontal cortical activities, and its inhibition extinguishes differences in anticipatory licking between the cues. Many dorsal frontal and medial prefrontal cortical neurons are task related. Subsets of these neurons are more excited by the low-reward-predicting cue or unrewarded outcomes than by the high-reward-predicting cue or rewarded outcomes, respectively. Task-related activities of these neurons and the others are counterbalanced, so that population activity appears dominated by licking. The reward-predicting cue and outcome history are most strongly represented in dmFrC. Our results suggest that dmFrC is crucial for initiating cortical processes to select or inhibit action.