The frontal lobe has, as some of its functions, the capability to project possible consequences as a result of current actions leading to the choice between worse and better actions, as well as the ability to give importance or suppress socially unacceptable responses. It is also important when it comes to integrating memories associated with emotions, where the frontal lobe use them to fit socially acceptable norms.
These are all functions that are affected in patients with schizophrenia, explaining why there is lower activity at the frontal lobe on them than on those of the healthy control which had normal levels of activity.