Biology 202, Spring 2005
Second Web Papers
On Serendip

Statistics provided by the National Center for Statistics and Analysis show that though adolescents aged 15-20 year old constitute only 6.4% of 194.3 million licensed drivers in the United States, they are involved in 14% of vehicular accident-related fatalities. In 2003 alone, 7,884 adolescent drivers were involved in fatal crashes, almost half (3,657) of which were caused by the teenage drivers. With such high accident rates, car collisions constitute the number one killer of Americans aged 15-20 years. 1). Traditionally, the frequency of adolescent automobile accidents has been attributed to factors such as alcohol intoxication, drowsiness and inexperience. While such explanations remain legitimate concerns, recent scientific research suggests that a significant component of the answer may in fact lie in the very structure of the teenage brain.

Until fairly recently, researchers and medical practitioners presumed that a brain's course of development corresponded to its physical growth, so that by the time the brain grew to 95% of its adult size around age six, it would be impervious to change. Earlier studies had determined that during gestation in the womb and the first 18 months of life, a child's brain undergoes a stage referred to as "overproduction," during which the brain produces an excessive amount of cells and neural connections. Those that are not used are "pruned," or removed, a process that scientists once believed to signal the end of the brain's development. 2)A longitudinal study conducted by Dr. Judith Rapoport of the National Institute of Mental Health, however, revealed evidence to the contrary. Utilizing MRI (magnetic resonance imaging) to scan the brains of 149 children and adolescents at two year intervals, Rapoport found that brains continue to develop well into adolescence, engaging in a second stage of overproduction characterized by a thickening of the brain's grey matter, the nervous tissue responsible for information processing. 3) The frontal lobes, a division of the cerebral cortex that manages emotions, personality, impulses and reasoning, undergo particularly significant growth, but by puberty, the second stage of overproduction beings to wane. 4)
for Teenagers." From this point on, the grey matter thins as it prunes away cells and synapses that have not been used and trained in the learning of new skills, such as violin playing. 2)

Significantly, the frontal lobes, which inhibit behavior, are one of the last divisions of the brain to finish developing. Researchers now speculate that this division of the brain responsible for making "executive decisions" based on methodical rational thinking and planning continues to develop throughout a person's early 20's. Thus, while the frontal lobes develop, other parts of the brain help process emotional information normally handled by fully-developed frontal lobes. A 1999 study conducted by Deborah Yurgelun-Todd, Director of Neuro-psychology and Cognitive Neuro-imaging at McLean Hospital in Belmont, Massachusetts, demonstrates as much. Expanding upon the research initiated by Rapoport, Yurgelun-Todd and colleagues showed adult and teenage subjects photographs of various facial expressions and asked them to articulate the illustrated emotion. While they deliberated, Yurgelun-Todd and colleagues employed MRI to scan the subjects' brains. Interestingly, they discovered that half of the teenage subjects incorrectly identified expressions of fear as sadness or shock, while every adult subject correctly identified the emotion of fear. Close inspection of the MRI revealed that the teenage and adult brains employed different parts of the brain to process the emotional information. 5) Compared to the teenagers, the adult subjects experienced heightened activity in their frontal lobes and lesser activity in the amygdale, the part of the brain involved with emotional and 'gut' responses. 4) This finding implies that teenage brains, by virtue of their immature frontal lobes, are not completely equipped to think through their behaviors and responses using the cognitive reasoning processes matured and available in normal adult brains. Until their frontal lobes have fully developed, adolescents and teenagers react to and interpret the external clues provided by the world through a lens significantly colored by emotional and "gut feeling" reactions, oftentimes relying on impulse rather than cool-headed critical analysis of a situation and potential consequences.

This insight into the developing structure of the teenage brain sheds new light on the sometimes seemingly perplexing and unnecessarily risky behavior of teenagers and adolescents, particularly when placed within the context of driving. Due to frequency of exposure and inevitability of interaction, it is reasonable to speculate that teenagers are frequently involved in car collisions because they misinterpret the behaviors of other drivers as threatening and therefore drive more aggressively, or perhaps some drive more recklessly because they do not fully think through the consequences of their decisions, particularly in high-stress driving conditions. But all of this is not to say that teenagers are incapable of processing situations and weighing the possible positive and negative outcomes of certain behaviors. Instead, it clearly makes evident that well beyond the age societal standards consider the start of adulthood, young brains interpret the world in ways markedly different from brains in which matured frontal lobes privilege rational judgment and behavior control over emotion-inspired impulsivity. This information must be taken into consideration when dealing with teenagers and adolescents in both personal and social capacities and guiding the development of their brains. During this crucial period of development, adolescents and teenagers should be encouraged to participate in the learning of various skills and activities. Never again will grey matter be more abundant, the brain more fruitful and plastic to change and development.

Moreover, these findings give rise to some interesting ethical questions. If scientific research demonstrates that in general, people do not maintain full possession of their cognitive faculties until their mid-twenties, these studies conceivably justify movements to enforce stricter guidelines on the behavior and rights of adolescents and young adults. In 1984, President Ronald Reagan signed into law the national 21 minimum drinking age legislation, since which alcohol-related car collisions and associated fatalities have decreased. 7) At the very least, these recent findings provide scientific evidence verifying the logic of this law, but for proponents of a higher drinking and/or driving age, this research stands as support for tighter regulations of teenage drivers. In the past few years, many states have already passed legislation limiting the use of cellular phones while driving and restricting the number of passengers a teenage driver may have in the car at one time.

Applying the same vein of thinking to a different context, opponents of the military draft can use this research to argue against the recruitment of individuals under the age of 25 for two reasons, the most obvious being that young men and women are simply too cognitively underdeveloped to function well in such situations in which they'd be forced to make decisions that would very literally be matters of life or death. If injuries and fatalities caused by car collisions are already a significant concern, one can only imagine the repercussions of arming a squad of young soldiers with machine guns and the authority to shoot. Secondly, the teenage and young adult years are the most formative of a person's life. If conditioned to observe and participate regularly in the systematic violence of military life, beliefs, norms and behaviors integral to this lifestyle will indubitably become ingrained within the young men and women, possibly replicating themselves once the individual returns to civilian life. Likewise, but to a different effect, the discovery that the brain maintains a significant degree of plasticity throughout adolescence gives rise to the hope that during this crucial period, individuals experience behavioral problems can change relatively easily. Regardless, the research discussed here verified, at the very least, that we have barely grazed the surface of the amazingly complex organ that is the human brain.

Web Sources

1) National Highway Traffic Safety Administration, NHTSA Traffic Facts: 2003

2) Frontline: Inside the Teen Brain, Interview with neuroscientist Jay Giedd.

3) National Institute of Mental Health, "Teen Brain: A work in progress."

4) Talukder, Gargi, "Decision-making is Still a Work in Progress for Teenagers."

5) Frontline: Inside the Teen Brain, Interview with director of neuropsychology and cognitive neuroimaging Deborah Yurgelun-Todd.

6) http://www.brainconnection.com/topics/?main=news-in-rev/teen-frontal

7) Mothers Against Drunk Driving, "On 20th Anniversary Of 21 Minimum Drinking Age Law."

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