A medical illustration of Phineas Gage's skull shows that the tamping iron passed through the front part of his brain, specifically damaging the prefrontal cortex. Based on the known functions of this brain region, which of the following outcomes is the most direct and well-documented consequence of his injury?

A 19th-century railroad worker survived an accident where a large iron rod was driven completely through his head, entering below his left cheekbone and exiting through the top of his skull. While he recovered physically and retained his memory and motor skills, his personality changed dramatically. He became impulsive, unreliable, and socially inappropriate, a stark contrast to his previously responsible and well-mannered nature. Based on the described path of the injury and the resulting behavioral changes, what is the most direct conclusion that can be drawn?