The prefrontal cortex (PFC) is the very front of the brain, located right beneath the forehead. It is in the anterior (front) region of the frontal lobes. Besides being the front of the brain physically, it is responsible for the executive functions, which include mediating conflicting thoughts, making choices between right and wrong or good and bad, predicting future events, and governing social control — such as suppressing emotional or sexual urges. The prefrontal cortex is the brain center most strongly implicated in qualities like sentience, human general intelligence, and personality.

When the pathways between the prefrontal cortex and the rest of the brain are damaged due to head injury, massive personality changes can result. The prototypical example is Phineas Gage, a railway worker whose prefrontal cortex was destroyed by a railroad spike. He survived, but friends and family say his personality changed completely. Weak interconnections between the prefrontal cortex and the rest of the brain have also been observed in criminals, sociopaths, drug addicts, and schizophrenics.

The prefrontal cortex has expanded greatly in size throughout homonid evolution, culminating in Homo sapiens, suggesting a strong selection pressure in favor of its continued growth. In the past five million years of human evolution, the size of the prefrontal cortex has increased sixfold. The size of the prefrontal cortex relative to the rest of the brain has also increased — throughout these five million years, the brain itself has only increased in size about threefold.

The prefrontal cortex is fed information from all the senses, and combines this information to form useful judgments. It constantly contains active representations in working memory, as well as representations of goals and contexts. Unfortunately, the prefrontal cortex, one of the most important areas in the brain, is also one of the most susceptible to injury. For this reason, it is always important to wear a helmet when participating in activities where head injuries are possible, such as biking.