How much of this actually holds up to scrutiny?
Fortunately, there are many aspects of this story that are falsifiable, and researchers have gone after it with robust energy. The findings are actually quite surprising. Some parts of the myth hold up well, while other parts don’t hold up at all. Here are the salient features:
First, it is not true that behaviors associated with executive function are unavailable to teenagers. Many executive functions are developed in the elementary years. It is an uneven transit, however: some kids show great executive maturity given their chronological age, and others show less skill.
It is true that executive function can be dramatically improved as children evolve through puberty, which may be part of the myth’s origin. The most time-sensitive behaviors are revealed in delayed gratification tests and in tests of planning and foresight tasks. Behaviorally, preadolescents don’t score very high on such tests. After the fires of puberty die down, however, they often score much higher.
These improvements correlate nicely with noninvasive imaging observations. Many fMRI images show dramatic increases in blood flow between prefrontal and parietal cortices as these children age (assayed under a variety of executive-testing conditions). These changes hold up, even when individual differences in brain structure are taken into account.
Behaviors like teenaged predilections toward sensation and risk-taking do not hold up as well, however. The idea is that regions in the brain naturally involved in reward-seeking should be more actively engaged in teenagers under tests that require reward seeking. They should then die down as the predilection for the behavior diminishes with age. The focus is usually on the nucleus accumbens and even the ventral tegmental areas, which makes sense, given their natural role in reward-seeking behavior.
Not everybody in the teenaged test cohorts shows such dramatic increases, however. Some researchers have actually found the opposite—a decrease in blood flow associated with increased risk-taking behavior. Some studies show increases to these areas in response to reward-seeking tasks, regardless of age. There are also the normal “chicken and egg” questions that plague so much of this type of research. Does the increase in blood flow create the behavior, or does the behavior create the increase in blood flow?
The Next Installment
As can be seen by looking at just 1 slice of neuroanatomical research and 1slice of behavioral research, much more work needs to be done before a complete explanation of teenaged brain development is in our grasp. And we have yet to address the central focus of this series: the relationship between whatever changes we agree actually exist and psychopathologies originating in adolescence. From the neuroanatomical or behavioral work mentioned above, what could possibly explain the data from the NCS-R?
Our next column is designed to address exactly these issues. There is substantial reason to believe that adolescent-based emerging psychopathologies are the result of interactions between 2 factors: anomalous adolescent maturation processes and psychosocial experience. It is as familiar as your latest ruminations on nature versus nurture put together this time in an attempt to explain a mental health statistic that is as familiar as it is startling.