Pre-action Neuronal Encoding of Task Situation Uncertainty in the Medial Prefrontal Cortex of Rats.

Humans and animals have a fundamental ability to use experiences and environmental information to organize behavior. It often happens that humans and animals make decisions and prepare actions under uncertain situations. Uncertainty would significantly affect the state of animals' minds, but may not be reflected in behavior. How to "read animals' mind state" under different situations is a challenge. Here, we report that neuronal activity in the medial prefrontal cortex (mPFC) of rats can reflect the environmental uncertainty when the task situation changes from certain to uncertain. Rats were trained to perform behavioral tasks under certain and uncertain situations. Under certain situations, rats were required to simply repeat two nose-poking actions that each triggered short auditory tone feedback (single-task situation). Whereas under the uncertain situation, the feedback could randomly be either the previous tone or a short musical rhythm. No additional action was required upon the music feedback, and the same secondary nose-poking action was required upon the tone feedback (dual-task situation); therefore, the coming task was uncertain before action initiation. We recorded single-unit activity from the mPFC when the rats were performing the tasks. We found that in the dual task, when uncertainty was introduced, many mPFC neurons were actively engaged in dealing with the uncertainty before the task initiation, suggesting that the rats could be aware of the task situation change and encode the information in the mPFC before the action of task initiation.