The prefrontal cortex (PFC) is where executive function lives. It is the CEO's office of the brain. The PFC plans, sequences, inhibits, holds information online in working memory, weighs consequences, and coordinates the rest of the brain in service of goals.
Two features of the PFC are clinically important to hold in mind from the start. First, it is the last region of the brain to fully develop. Myelination of PFC connections is not complete until the mid-twenties. This is why adolescents make the decisions adolescents make: their executive office is still being wired. The impulsivity, the underweighting of long-term consequences, the social-reward sensitivity — these are not character defects, they are developmental realities.
Second, the PFC is the first region of the brain to decline in normal aging. Executive function tasks like the Trail Making Test or the Wisconsin Card Sort decline before memory does. The slight slowness in switching tasks, the increased reliance on familiar routines, the difficulty learning new software — these track with PFC aging well before frank memory loss appears. In many older patients, the cognitive complaint they bring to clinic is actually executive, not amnestic, even though they describe it as "my memory."
The PFC has three major subdivisions, each with distinct functions, and these are worth knowing because they map directly onto common clinical presentations. The next concepts will visit each in turn: dorsolateral prefrontal cortex (DLPFC), ventromedial prefrontal cortex (VMPFC), and orbitofrontal cortex (OFC).
The PFC receives dopamine from the VTA through the mesocortical pathway, which we met in Stage 2. PFC dopamine signaling follows an inverted U-shaped curve: too little or too much both impair function, with optimal performance at the middle of the range. We will dwell on this in the last concept of this stage. For now, hold the idea: a chemical dial in the executive office, with a narrow optimal range.
Damage to the PFC — from stroke, tumor, trauma, neurodegeneration, or developmental anomaly — produces deficits that often look like personality change rather than cognitive impairment. The patient may have normal language, normal memory, normal motor function, normal sensation. But they cannot plan. They cannot inhibit. They cannot follow through. They cannot weigh long-term consequences against short-term rewards. The cumulative effect is the loss of competent self-direction, even when no isolated function is obviously broken.
Hold the office. Over the next concepts we will meet each subdivision and see how its specific failures produce specific clinical syndromes — from the cognitive symptoms of schizophrenia to the disinhibition of frontotemporal dementia to the inability to make sound decisions in Phineas Gage's nineteenth-century case that opened the field.