The cerebral cortex of the brain has four paired lobes.
one of these four paired lobes is the frontal lobe and it occupies 2/3rds of the entire human brain.
the frontal lobe is associated with performing tasks such as speech and language production, walking and running, classifying and identifying objects, reacting to feelings, forming memories, forming the personality of a person, and attention involving tasks.
Since after the injury, Zack has an altered personality and his reaction to the situation has changed, this points out to the fact that he is most likely suffering from frontal lobe injury.
