The entirety of the frontal cortex can be considered the "action cortex", much as the posterior cortex is considered the “sensory cortex". It is devoted to action of one kind or another: skeletal movement, ocular movement, speech control, the expression of emotions, etc. In humans, the largest part of the frontal cortex, i.e. the Prefrontal cortex, is responsible for internal, purposeful mental action, commonly called reasoning or Prefrontal Synthesis.
The function of the PFC involves the ability to project future consequences that result from current actions (Ni and Ne). PFC functions also include override and suppression of socially unacceptable responses as well as differentiation of tasks (Fe/Fi and Te/Ti).
Prefrontal synthesis (PFS, also known as Mental Synthesis) is the conscious purposeful process of synthesizing novel mental images. PFS is neurologically different from the other types of imagination, such as simple memory recall and dreaming. Unlike dreaming, which is spontaneous and not controlled by the prefrontal cortex (PFC), PFS is controlled by and completely dependent on the intact lateral prefrontal cortex. Unlike simple memory recall that involves activation of a single neuronal ensemble (NE) encoded at some point in the past, PFS involves active combination of two or more object-encoding neuronal ensembles (objectNE). The mechanism of PFS is hypothesized to involve synchronization of several independent objectNEs. When objectNEs fire out-of-sync, the objects are perceived one at a time. However, once those objectNEs are time-shifted by the lateral PFC to fire in-phase with each other, they are consciously experienced as one unified object or scene.