How did researchers first learn about the functions of the frontal lobes? What are those functions? What are the consequences of severe frontal lobe damage? What does this tell us about personality?

The frontal lobes, also known as the right and left frontal cortexes, play crucial roles in memory, motivation, attention, planning, decision-making, and voluntary movements such as walking. The left frontal lobe controls muscles on the right side of the body, while the right frontal lobe controls muscles on the left side of the body. In the early 1900s, many doctors and medical professionals adopted lobotomies as treatments for mental illnesses. According to neurologist Egas Moniz, a lobotomy (which involves removing or scraping away parts of the frontal lobe) deadens or blunts the emotions and the personality, which would "cure" a person of mental illness (such as depression). Starting in the 1950s, this procedure was largely abandoned, especially because of the damage it caused to the frontal lobes.
One of the most common symptoms of frontal lobe damage is a decrease in inhibition, judgment, and decision-making abilities. People who experience frontal lobe damage may respond to situations inappropriately or find themselves unable to make what were once simple decisions. They also might lack motivation, causing them to lose interest in activities in which they once engaged. Thus, a person with frontal lobe damage might, in a sense, lose characteristics of their personality.