Frontal lobe development begins soon after conception and continues until a person reaches young adulthood. The most rapid change in the frontal lobe occurs right before adolescence, when neuron growth surges. As a child enters puberty, the brain begins trimming away excess neurons as gray matter begins growing, until it reaches its adult weight in a person's early to mid 20s.
A child is born with many neurons and connecting synapses. Links used frequently grow stronger while those rarely used are considered non-essential and pruned away. At the same time, new synapses continue to form. This process of brain development in adolescence controls inhibition, emotional response, decision making, and long-term planning.
When infants are six to 12 months of age, frontal lobe growth occurs in spurts as a child learns to walk and talk. Important information is retained during this time and non-essential data gets pruned away during certain critical development points.
Some scientists believe delayed frontal lobe development explains why some adolescents show poor impulse control and engage in risky behaviors. During this period of rapid development, the brain's amygdala section, the area responsible for gut reaction and heightened arousal, might become overactive. At the same time these changes occur, myelin, tissue surrounding nerves, begins growing in the frontal brain.
Myelin forms connections with different parts of the brain and sends signals based on experiences. The brain is not fully functional until these connections become intact. During this period, teens develop the ability to control impulses, including sexual urges; set goals; determine right from wrong; and hone their social skills.
If development in this part of the brain fails to occur, it might lead to attention deficit hyperactivity disorders or psychological problems. One study linked poor frontal lobe development to antisocial personality disorder. A deficit in brain growth might also hinder concentration and decision-making skills. Researchers found illicit drug use, premature birth, and brain injury also affect how this region of the brain develops.
Experts believe brain growth occurs at a different rate in individuals. The brain of a 16-year-old might be fully developed, while a sibling’s brain might not reach full maturity until his mid-20s. These factors have been used in defending teens who commit crimes by arguing they lacked the ability to control impulses because of immature brain development.