The emerging science of neuro-development is providing a new framework for viewing adolescent risk taking, including decisions by young people to use alcohol and other drugs. This new research, aided by sophisticated brain imaging technology, has documented the surprising finding that the human brain is still maturing in significant ways during the adolescent years (Giedd, 2004). The way the brain develops during adolescence may help explain why youth sometimes make decisions that seem to be quite risky. Plus brain development research also shows that the maturing brain may be particularly vulnerable to the acute effects of drugs, and that drug use during adolescence may significantly increase a young person's risk for developing a substance use disorder later in life (Casey, Jones, & Hare, 2008).
This article will explore how adolescent brain development is a useful framework to understand adolescent drug use and abuse by looking at how brain development leads to risky behavior, how drugs affect brain development, and how we can use this knowledge in our prevention and intervention efforts. But first, we need to understand how the brain matures during adolescence.
WHAT NEUROSCIENCE SAYS ABOUT BRAIN MATURATION
The pioneering research of Jay Giedd and colleagues at the National Institute of Mental Health (Giedd, 2004) has produced evidence that the brain is still developing during adolescence and young adulthood. The brain grows an excessive number of connections between brain cells prior to adolescence, but at about age 11 or 12, the brain begins the processing of "sculpting" or pruning-back a significant proportion of these connections (Giedd, 2004). This pruning is a healthy process because it clears out unused wiring to make room for faster and potentially more efficient information processing. Also, pruning helps the brain to build the longer chains of nerve cells needed during adulthood for complex decision making. The pruning process appears to follow two general principles. One is the "use-it-or-lose-it" principle (Giedd, 2004), that is, the nerve cells that are frequently used during childhood are strengthened and the ones that are not activated or are infrequently used are eliminated. Dr. Giedd describes this principle in the following way: "Ineffective or weak connections are pruned in much the same way a gardener would prune a tree or bush, giving the plant the desired shape" (as quoted by Wallis, 2004; p. 58).
The second principle about the pruning process is that it tends to occur in the direction of back to front of the brain (Gogtay et al., 2004). The front area of the brain, particularly the pre-frontal cortex, is referred to as the "CEO of the brain." It is associated with logical reasoning and regulating impulses, and is the area believed to be primarily associated with guiding decisions that a person makes. During adolescent brain development, it is believed that the brain regions located further back, particularly the limbic region--which is associated with processing emotions and memories--matures earlier than the pre-frontal cortex region (Gogtay et al., 2004). As psychologist David Walsh writes, it is as if a...