The role of the rat medial prefrontal cortex in complex decision-making impairments

Damage to the medial prefrontal cortex (mPFC) often leads to problems characteristic of addiction, such as impulsivity and insensitivity to future consequences. To learn more about the role of this region, we studied the effects of mPFC lesions in rats on decision making processes related to behavioral addiction. We hypothesized that rodents with mPFC lesions would be less flexible when faced with changing task contingencies resulting in a diminished ability to obtain as much reward as comparable control animals and that this would be due to a deficit in the rats’ ability to generate appropriate expected values when presented with multiple choice options. To this end, we designed a rodent decision-making task, the N-Arm Bandit Task, to test these hypotheses. We found that damage to the mPFC decreased the ability of rats to obtain reward after a change in reward contingency and had a modest effect on the likelihood of rats to perseverate on ports that were previously rewarding. Finally, we found that PL lesions had a major impact on reward processing in that the reinforcement learning model used to fit the rats’ behaviour was unable to meaningfully describe the performance of the PL damaged rats, while the behaviour of the control animals was well described by the model.