Learning-related changes in response patterns of prefrontal neurons during instrumental conditioning

Abstract

A crucial aspect of organizing goal-directed behavior is the ability to form neural representations of relationships between environmental stimuli, actions and reinforcement. Very little is known yet about the neural encoding of response–reward relationships, a process which is deemed essential for purposeful behavior. To investigate this, tetrode recordings were made in the medial prefrontal cortex (PFC) of rats performing a Go–NoGo task. After task acquisition, a subset of neurons showed a sustained change in firing during the rewarded action sequence that was triggered by a specific visual cue. When these changes were monitored in the course of learning, they were seen to develop in parallel with the behavioral learning curve and were highly sensitive to a switch in reward contingencies. These sustained changes correlated with the reward-associated action sequence, not with sensory or reward-predicting properties of the cue or individual motor acts per se. This novel type of neural plasticity may contribute to the formation of response–reinforcer associations and of behavioral strategies for guiding goal-directed action.