The overall interest of our lab is to understand how model-based inference is accomplished by neural circuits. Over the past few years we have focused on the role that the rodent medial prefrontal cortex (mPFC), an area homologous to primate anterior cingulate cortex (ACC), plays in encoding the internal representation of the rules of the environment. We have designed behavioral tasks in which these rules change suddenly or evolve in a very complex manner-in some cases eliciting abrupt changes in the workings of the internal model and in others leading to the abandonment of attempts at model construction. Recordings of the activity of neuronal ensembles in ACC revealed that moments of abrupt change in behavioral strategy are associated with sudden transitions in the pattern of neural activity across the mPFC, one interpretation of which is that such changes signify a reset of prior expectations.
In addition, inactivation of ACC by local muscimol administration revealed that the influence of ACC on behavior is suppressed when attempts to build an internal model are unsuccessful. Finally, selective enhancement or suppression of Locus Coeruleus input into the ACC, respectively, abolished or restored model-based control of behavior. In combination, our observations argue in favor of the idea that ACC represents an animal's beliefs about the environment's governing rules. I will discuss our latest evidence in further support of this notion, with a concentration on the role of the ACC in directing exploratory decisions during model-based behavior. In addition, I will outline how we are using a combination of viral and optogeneic tools that we have recently developed to begin to dissect how the presumed model encoding area, the ACC, communicates with the downstream motor centers in guiding the animal through efficient exploration of different hypotheses about the rules operating in its environment.