I haven’t post for a week. Its been a crazy one. Here is part of what I was working on: a paper on why teens are…um…irrational at times. Its pretty fascinating and I figure I might as well get more out of it than a grade for a psych 101 class.
Frontal Lobe Development In the Teenage Brain
a paper submitted in partial fulfillment of the requirements for
General Psychology 201A
Fred C. Miller, MS
Portland Community College
In reference to parenting during the teenage years, my mom says: “Just hold on and make it through. That’s all you can ask for.” She is not alone in this opinion. Most parents don’t understand why their angelic children start acting out and doing things they wouldn’t have considered a year or a month before. This paper is a discussion of teen brain development and how it causes teens to exhibit extreme behaviors and become more susceptible to drug use. I will first discuss teen frontal lobe development and follow with how this development affects behavior and emotions and last look at this development with regard to addiction and drug use.
A human brain’s outermost portion, the cerebellum has multiple sections and layers. The foremost portion, right behind the forehead, is called the frontal lobe. This lobe the is executive portion of your brain and associated with higher cognitive function such as goal-oriented decision making, and emotional control. (Geidd, Frontline, 2009) Teen brain development of the frontal lobe is a changing relationship between white brain matter, or myelinated neurons, and gray brain matter, unmyelinated neurons. Myelination is the addition of the myelin sheath around the axon of a neuron insulating it and creating faster communication between neurons. (Meyers, 2010, p.49)
Your brain is 95% of its size at age 5 or 6. (Frontline, 2000) It is this last 5%, and the transformation from gray to white matter, that influences the teen years and therefore, sets us up for adulthood. The relationship of gray and white matter in the human brain during adolescents is not linear. The teen brain develops in two different ways. The first is linear and a second, recently discovered, is counter-intuitive and shines a new light on brain maturation and the paradoxical relationship between gray and white matter.
A mature brain has a thin layer of gray matter on the surface 2-3 millimeters thick of unmyelinated axons. (Shipp, 2007, p. 443) Under this layer is a thick layer of white, myelinated, matter. The separation of gray and white matter is necessary for faster neural communication. “If grey and white were intermixed, the average separation of neurons would be greater, creating extra neural ‘wiring’. The speed of cortical computation would suffer accordingly.” (Shipp, 2007, p.443)
As we develop, the outer cortex is thicker than 2-3 millimeters and is transformed into white matter as it becomes myelinated. White matter develops linearly as we age, sometimes until the early 30s. The development of white matter in the frontal lobe over time is integral for the development of mature cognitive thought. Jay Giedd, in his article The Teen Brain: Insights from Neuroimaging, uses MRIs over the course of childhood into adulthood to look at the development and distribution in the teen brain. (Geidd, 2007, p.335) “The rate of increase [of white matter] is age dependent  and can increase by as much as 50% in a 2-year period in small regions of interest ; but at the lobar level (frontal, temporal, and parietal lobes), developmental WM [White Matter] trajectories are similar. (Geidd, 2007, p. 337)
The expansion of white matter continues into people’s late 20s and now, some think, into people’s 30s. “Normally this mental merger is not completed until somewhere between ages 25 and 30—much later than these two neurologists were taught in medical school.” (Ruder, 2008)
This explains why teens are intelligent yet often behave emotionally or irrationally. This white matter thickening and gray matter thinning of the cerebellum occurs from the back of the head, the occipital lobe forward, to the frontal lobe where higher cognitive thought processes such as: reasoning and goal-oriented decisions, occur. (Sowell, 1999, p.860) Put simply, the frontal lobe, or CEO section, is the last to develop. “They looked for signs of myelin, which would imply more mature, efficient connections, within gray matter. As expected, areas of the frontal lobe showed the largest differences between young adults and teens.” (NIMH, 2001, p.1)
Francese E. Jensen M.D., an expert on the teenage brain, explains further: “we get older, we develop better, stronger connections between our different regions of the brain. And it actually develops from the back of your brain to the front.” (Jensen, 2009)
The thickening of white brain matter over time is only the first portion of what makes teen brain development so unique. Pre-pubescent children over-produced gray matter in the frontal lobe. Previously experts believed over production of gray matter happened only in fetal development and infancy. “What is most surprising is that you get a second wave of overproduction of gray matter, something that was thought to happen only in the first 18 months of life.” (Begley, 2000, p. 59)
Elizabeth Sowell, in her examination of hundreds of MRI scans finds the same results. “In contrast, changes in volume of cortical gray matter were nonlinear and regionally specific. Gray matter in the frontal lobe increased during pre-adolescence with a maximum size occurring at 12.1 years for males and 11.0 years for females, followed by a decline during post-adolescence that resulted in a net decrease in volume across this age span.” (Sowell,1999, p.861)
They now know that gray matter is over-produced until the onset of puberty. With puberty gray matter over-production stops. “In the frontal part of the brain, the part of the brain involved in judgment, organization, planning, strategies — those very skills that teens get better and better at — this process of thickening of the gray matter peaks at about age 11 in girls and age 12 in boys, roughly about the same time as puberty.” (Geidd, 2000, Frontline)
After the start of puberty the process of pruning begins. Pruning is the deletion of neural networks that are not used. Think of a tree that grows wildly until a gardener comes and trims the tree to a desired shape that may lead to more flowering and better health. The teenage brain is similar. “The connection between GM [Gray Mattter] volume reductions, EEG changes, and synaptic pruning is also supported by an MRI and quantified EEG study of 138 healthy subjects aged 10–30 years; this study found curve linear reductions in frontal and parietal GM were matched by similar curvilinear reductions in the EEG power of the corresponding regions .” (Giedd, 2008, p. 338) Giedd is saying the brain prunes areas where there is little brain activity as shown on MRIs and EEGs.
Pruning allows the brain to get rid of unused neurons therefore reserving energy for neural pathways that are heavily used and creating stronger connections. However, this process of creating strong white matter connections in the frontal lobe is just beginning with puberty and one of the main functions of adolescence.
The teen brain is not just an adult brain with less experience. It is a brain with comparatively large amounts of gray matter that, as neural connections and pathways are made and the unused deleted, is slowly being transformed into more white matter; especially in the frontal lobe. This means the teen brain is at the peak of learning, yet without the executive reasoning of an adult brain. One could say that teens know right from wrong but may not act accordingly. Since the neural pathways are not yet efficient, teens use other parts of their brain to compensate. An example of this is a ‘gut response’ to situations instead of a controlled response. In an article on teenage culpability the American Bar Association discusses just this: “Dr. Deborah Yurgelun-Todd of Harvard Medical School has studied the relation between these new findings and teen behavior and concluded that adolescents often rely on emotional parts of the brain, rather than the frontal lobe.” (American Bar Association, 2004, p. 2)
Specifically Yourgelun-Todd studied MRI scans taken of adolescent and adult participants’ brains as they described the emotions of people in various pictures. (Frontline, 2000) The adults’ MRI showed use of the frontal lobe while teens used more of the amygdala, an emotion control center, portion of the brain. “She [Dr. Deborah Yurgelun-Todd] found that compared to adults the teens’ frontal lobes (the seat of goal-oriented rational thinking) are less active and their amygdala (a structure in the temporal lobe that is involved in discriminating fear and other emotions) is more active. The teens often misread facial expressions, with those under the age of 14 more often seeing sadness or anger or confusion instead of fear.” (Cornell University, 2002, p. 2) When a teen responds unexpectedly to a situation, such as screaming and yelling when asked to do the dishes, it could be because their frontal lobe does not have as much control over their response as the emotional amygdala.
Since the teen brain is at its peak of learning capability it is a lot like a block of stone waiting to be carved into a statue. There is a masterpiece waiting to come out in its neural connections as the unused are pruned away. Also, like a statue, once a portion is damaged, it can’t rebuild. Thus the events of the teenage years have a heavy influence on subsequent brain maturation. “It’s a time of enormous opportunity and of enormous risk. And how the teens spend their time seems to be particularly crucial. If the “Lose it or use it” principle holds true, then the activities of the teen may help guide the hard-wiring, actual physical connections in their brain.” (Frontline, 2000)
One sort of learning that can cause damage to the susceptible teen brain is addiction. Teen addiction can happen faster and be stronger, and result in greater brain damage. “Recent studies, only in the last five years, have shown that addiction actually does use some of the same molecular biology and physiology as learning. Therefore, teen brains can get addicted faster and stronger than adult brains and teenagers can have a lifelong problem with trying to shed an addiction that has been acquired as a teenager.” (Jensen, 2009)
Jensen goes on to say that not only can the addiction be stronger but since the teenage brain is still in process, the effects can be more drastic. For example alcohol toxicity can be more damaging, marijuana use can lead to more memory impairment, and, in the case of a nicotine study with rats, the brain responded up to 10 times more intensely in a teen rat over an adult rat with the same dosage. (Jensen, 2009)
Teen brains are complicated. It is my view there is a lot more to be discovered with teen frontal lobe development especially the changing relationship of the frontal lobe and limbic system, and with the effect of drug use during adolescence and resulting effects on adulthood. This is the main weakness of my argument. The discovery of gray matter development in the frontal lobe is roughly ten years old and most articles cite Giedd’s research as a main source. There must be a lot more studies underlining his work on frontal lobe development.
It is also my view that the key to shaping healthy adults may be education on teen brain development during the teen years. This is what Frances Jensen seeks to do. She gives presentations to teens, educators, and experts on teen brains called Teen Brain 101. “…the idea is if we give them a sense that they actually might be more vulnerable to certain things then they might want to make different choices when it comes to substance use or putting themselves at risk. And also to tell them that they have probably better learning capacity now than ever again for certain types of learning and to embrace that and to really try to use this time in their lives.” (Jensen, 2009)
In conclusion, The teen brain changes more than previously thought. Not only is there an increase in white matter from the back to front of the head, but an unexpected growth of gray matter in the frontal lobe right before puberty. This means that teens, with the intelligence of adults, may have rash or unexpected behavior and that, at the peak of learning, they are more susceptible to addiction and what they do now has greater effect on later life. It is my viewpoint that more research is necessary to fully understand the teenage brain but also that the teens themselves need education on their own brain development so they can make better choices.
1. American Bar Association. (2004)Cruel and Unusual Punishment: The Juvenile Death Penalty. 1-4
2. Bradley-Ruder, D., (2008). The teen brain. Harvard Magazine. Retrieved from http://harvardmagazine.com/2008/09/the-teen-brain.html
3. Begley, Sharon. (February 28, 2000). Getting inside a teen brain. Newsweek, 135(9): 58-59.
4. Cornell University, University of Rochester, and the NYS Center for School Safety. Adolescent Brain Development. May 2002.
5. Dahl, R. E., University of Pittsburgh Medical Center. Revtrieved from http://www.wccf.org/pdf/dahl.pdf
6. Dreifus, C., (2009, Nov. 30) Developmental psychologist says teenagers are different. New York Times. Retrieved from http://www.nytimes.com/2009/12/01/science/01conv.html?_r=1
7. Galvan, A., Hare, T. A., Parra, C. E., Penn, J., Henning, V., Glover, G., Casey, B. J., (2006) Earlier Development of the Accumbens Relative to Orbitofrontal Cortex Might Underlie Risk-Taking Behavior in Adolescents. The Journal of Neuroscience, 26(25):6885– 6892
8. Giedd, J., (2002). Inside the teenage brian. Frontline. Retrieved from
9. Giedd, J.N. (2008). The Teen Brain: Insights from Neuroimaging. Journal of Adolescent Health. 42: 335–343
10. Jensen, F. E. (2009) On the teen brain. Children’s Hospital Boston. Retrieved from
11. National Institue of Mental Health. Teenage Brain: A work in progress. (2001). Retrieved from http://www.nimh.nih.gov/health/publications/teenage-brain-a-work-in-progress-fact-sheet/index.shtm
12. Shipp, S., (2007). Structure and function of the cerebral cortex. Current Biology. 17(12): 443-449.
13. Sowell, E. R., Thompson, P. M., Holmes, C. J., Jernigan, T. L., Toga, W. A. (1999) In vivo evidence for post-adolescent brain maturation in frontal and striatal regions. Nature America Inc. 859-661. Retrieved March 1 from: http://neurosci.nature.com
14. Yurgelun-Todd, D., (2002). Inside the teenage brain. Frontline. Retrieved from http://www.pbs.org/wgbh/pages/frontline/shows/teenbrain/interviews/todd.html