Final answer:
After his accident, Phineas Gage showed erratic behavior due to the injury to his prefrontal cortex, which is consistent with reports of his personality change from amiable to irritable and temperamental.
Step-by-step explanation:
Compared to Phineas Gage's personality before his accident, after the accident Gage was erratic. The injury caused by a large iron rod passing through his prefrontal cortex resulted in significant changes to his behavior. Prior to the accident, Gage was known to be a hardworking, amiable man, yet after the incident, he became irritable, temperamental, and exhibited a marked decline in his work ethic. Although some accounts may have overstated these personality changes, it is clear that the trauma did have a considerable effect on his demeanor. Gage later adapted to his condition and even managed to work as a stagecoach driver, indicating the brain's capacity for recovery and adaptation after serious injuries.