Final answer:
Phineas Gage's personality change was a result of damage to his frontal lobes, specifically the prefrontal cortex.
Step-by-step explanation:
The tragedy that happened to Phineas Gage resulted in damage to his frontal lobes, specifically the prefrontal cortex. The prefrontal cortex is responsible for planning, judgment, reasoning, and working memory. Damage to this area can result in changes to personality, mood, and behavior.