Achieving goals in changing environments requires the course of action to be selected on the basis of goal expectation and memory of action-outcome contingency. It is often also essential to evaluate action on the basis of immediate outcomes and the discrimination of early action steps from the final step towards the goal. Recently, in single-cell recordings in monkeys, the neuronal activity that appears to underlie these processes has been noted in the medial part of the prefrontal cortex. Medial prefrontal cells were also active when the subjects extracted the rules of a task in a novel environment. The processes described above might play important roles in rule learning.