Hockenbury Discovering Psychology 5th txtbk

Adolescence397Researchers are still not certain what causes this late childhoodsurge of cortical gray matter, but they know it is not dueto a production of new neurons. Rather, the size, complexity,and connections among neurons all increase. This increase ingray matter peaks at about age 11 for girls and age 12 for boys(Durston & others, 2001).Pruning Gray Matter from Back to FrontThe color-coded series of brain images below shows the courseof brain development from ages 5 to 20 (Gogtay & others,2004). Red indicates more gray matter; blue indicates less graymatter. Courtesy of UCLA neuroscientist Paul Thompson, youcan also watch brief time-lapse “movies” of the changing brainat the following web site:http://www.loni.ucla.edu/~thompson/DEVEL/dynamic.html.The MRI images reveal that as the brain matures, neuronal connectionsare pruned and gray matter diminishes in a back-to-frontwave. As pruning occurs, the connections that remain arestrengthened and reinforced, and the amount of white matter inthe brain steadily increases (Giedd, 2009; Sowell & others, 2003).More specifically, the first brain areas to mature are at theextreme front and back of the brain. These areas are involvedwith very basic functions, such as processing sensations andmovement. The next brain areas to mature are the parietal lobes,which are involved in language and spatial skills.The last brain area to experience pruning and maturity is theprefrontal cortex. This is significant because the prefrontal cortexplays a critical role in many advanced or “executive” cognitivefunctions, such as a person’s ability to reason, plan ahead,organize, solve problems, and decide. And when does the prefrontalcortex reach full maturity? According to the MRI studies,not until a person reaches their mid-20s (Gogtay & others,2004a).This suggests that an adolescent’s occasional impulsive orimmature behavior is at least partly a reflection of a brain thatstill has a long way to go to reach full adult maturity. During adolescence,emotions and impulses can be intense and compelling.But the parts of the brain that are responsible for exercisingjudgment are still maturing. The result can be behavior that isimmature, impulsive, unpredictable—or even risky.SideViewAge5 yrs 8 yrs 12 yrs 16 yrs 20 yrsTopViewGraymattervolumeexample, early-maturing girls tend to be more likely than late-maturing girls to havenegative feelings about their body image and pubertal changes, such as menarche(Ge & others, 2003). Compared to late-maturing girls, early-maturing girls are lesslikely to have received factual information concerning development. They may alsofeel embarrassed by unwanted attention from older males (Brooks-Gunn & Reiter,1990). Early-maturing girls also have higher rates of teenage pregnancy and are atgreater risk for unhealthy weight gain later in life (Adair & Gordon-Larsen, 2001;Lien & others, 2006).Early maturation can be advantageous for boys, but it is also associated with risks.Early-maturing boys tend to be popular with their peers. However, although theyare more successful in athletics than late-maturing peers, they are also more susceptibleto behaviors that put their health at risk, such as steroid use (McCabe &Ricciardelli, 2004). Early-maturing boys are also more prone to the symptoms ofdepression, problems at school, and engaging in drug or alcohol use (see Ge &others, 2001, 2003).