The teenage brain is different in function from the brain of children and adults. Teens react and respond differently than adults and children. During the teen years there is an increase in risk taking and sensation seeking and an interest in greater peer affiliation. Historically from an evolutionary perspective this leads to greater physical separation between family members and a decreased risk of genetic inbreeding and a preference for genetic diversity. This period allows us to adapt and respond to changes that have forced us to grow and react in an active yet plastic fashion. Although this process occurs throughout our lives it is especially evident during the teen and young adult years. It is felt that critical periods of rapid change may relate to various ages of rapid learning and that various areas of the brain mature relatively late. Your brain reaches 93% of its size by age 6 years. Learning comes not from getting bigger but rather from specializing and getting better in connectivity. The brain improves in function by becoming more specialized in relation to its response to the environment.
Teenagers have a fundamental ability to adapt to change in their environment. They have an ability to learn, interact and respond to the environment. In recent years the rapidity of exposure to new experiences has increased as has the ability to interact and respond to these changes. It is this plasticity that provides adolescents and young adults’ opportunity and vulnerability.
Each cubic millimeter of brain contains about 2 miles of axons, 90,000 neurons, one quarter mile of dendrites and 4,500,000 synapses. Clarity from an understanding of the function of this complex structure can be very difficult and it is easy to over interpret the information. As a child ages into adulthood the white matter called myelin increases in a linear fashion and the speed of transfer of information increases. White matter is the same throughout the brain. White matter allows information to be encoded into the brain in a much faster fashion. Chemicals are released that decrease arborization (growing extra branches and roots) and the formation of new connections. This pruning of synapses allows us to integrate and tie information together as we age. The pruning and arborization occurs throughout our entire lives. As we progress from newborn to toddler and then preschool and school age years the growth permits maturation and connectivity that improves brain function and behavioral responses. During these periods genetic and environmental factors facilitate or inhibit the process.
This connectivity which is both modular (chapters in a book) and local (the letters with words and sentences or a paragraph) allows for differentiation between the convergence between specific pieces of data and our responses to stimuli.
The gray matter in the brain reaches a peak in the early teen years and follows an inverted u shape from preschool to age 21 years. The gray matter curve is different for different parts of the brain. For the frontal lobe which is involved in decision making and executive function it reaches a peak for girls at about age 11 ½ years and for boys at 13 ½ years. It appears that this rise and fall is seen in all components of brain function including synaptic density. This is consistent with the general pattern of function in nature where there is an initial overproduction and then a weaning of structural components. This culling allows for functional improvements in responses seen by adults compared to teens for judgment, long range planning and impulse control.
As the brain ages from childhood through puberty and into young adult years there is an overall change in the balance of frontal lobe and limbic system activity with the limbic system showing its highest response pattern during puberty and the frontal lobes appearing later with enhanced decision making in terms of increased delayed gratification capability. Activation patterns change from diffuse to focal and there is evidence of increased integration of brain function and decision making and there is an increase in connectivity speed and efficiency.
The roles of nature (genes) and nurture (environment) are being studied intensely throughout all periods of brain growth. This is a complex issue due to potential sexual variations and time mediated responses. In addition, since many genes may be activated at certain ages, this time mediated activation has implications in terms of the mechanism and trajectory of brain changes and functions. Although the brain trajectory for boys and girls is different the ultimate trajectory is similar. Girls seem to peak from 18 to 30 months earlier than boys in terms of most structural measures of brain function and male brains seem to be more variable than female brains. Overwhelmingly males and females are more similar than different in terms of ultimate brain functioning and the roles of the sex chromosomes, environment and hormones are still being determined and may be complexly mediated by the individual’s age.