Addendum—Developing a Picture of the “Amazing Teen Brain”

Share this Blog post

As I was finishing up the previous post I flashed on an article that I read a number of years ago on The Amazing Teen Brain, which happens to be the title to Jay Giedd’s 2015 paper that appeared on the web site in June. Dr. Giedd is a professor at UC Santa Barbara in the psychiatry department. In my opinion Dr. Giedd’s article is not only wildly important but shines a light on the topics mentioned in the previous post that focuses on the work of the Yeagers. In this addendum I would like to pull out a few key points from The Amazing Teen Brain and attempt to tie them back to the information presented in the previous post. This post assumes you have read the previous post first.

Dr. Giedd primarily does MRI (magnetic resonance imaging) studies on teen brains. From the get-go Dr. Giedd makes it clear that human brains are incredibly complex and very dynamic. Brain scientists will look at brain processes as taking place from top to bottom, from left brain to right brain, from front to back, and along all paths in between. Simply put the brain is comprised of a number of various components (like our friend the prefrontal cortex) that are organized, arranged, and connected in a very complex and dynamic fashion.

If this complexity were not enough, evolution has produced a process of brain development typified by abundance followed by pruning. As Dr. Giedd puts it, “Brain development like other complex processes in nature, proceeds by a one-two punch of overproduction, followed by selective elimination.” Dr. Giedd continues, “[M]any cognitive advances arise during a sculpting process in which unused or maladaptive brain cell connections are pruned away.” Dr. Giedd alerts us to the fact that this process of overproduction followed by selective elimination provides us with great promise as well as great peril.

If this so-called “feast and famine” process (as I’m calling it) goes well then we may expect such things as better social relationships, better ability to plan for the future, and better overall judgement and discernment skills. Gee, sounds a lot like the outcomes Walter Mischel found when he followed high delayers into adulthood. But when it goes wrong, yeow! “Adolescence is the peak time of emergence for several types of mental illnesses, including anxiety disorders, bipolar disorder, depression, eating disorders, psychosis and substance abuse,” writes Dr. Giedd. To drive this point home Dr. Giedd tells us that “almost all the abnormal brain findings in adult schizophrenia resemble the typical changes of adolescent brain development gone too far.” I’m sorry but that’s a showstopper statement. I’m not going to talk about the 2008 article(1) by Karlsgodt et al. from which the following graph comes. However I wished to give you a graphical sense for what Dr. Giedd is talking about.




To Dr. Giedd’s point, as long as pruning stays above a certain threshold, then things look good for our “feast and famine” process of brain development. However if pruning drops below that threshold, perhaps because of “irregular, prolonged, or excessive pruning” (as the graph points out), then we may expect the types of mental illness Dr. Giedd lists above. Today our society is plagued by such things as teen-involved shootings and teen opioid addiction. Given this reality I have to wonder if as a society we are now flirting with the “psychosis threshold” indicated above.

Now, Dr. Giedd talks a lot about another developmental vulnerability that’s of concern: a mismatch between when the limbic system (typically found in the middle brain) comes online versus when the prefrontal cortex (typically found in the upper brain) comes online. Once again, the PFC is typically associated with the development of EF or Executive Function. Decision-making would be an example here. The limbic system of the brain is associated with emotions and emotional response to outside stimuli (like the guy who just cut you off in traffic).

According to Dr. Giedd’s research, the limbic system (as evidenced by the onset of puberty at ages 10 to 12) is coming online at early and early ages worldwide. In contrast to this trend is the observation that the PFC is coming online at later and later ages, sometimes as late as 25. “What most determines teen behavior, then, is not so much the late development of executive functioning or the early onset of emotional behavior but a mismatch in the timing of the two developments,” states Dr. Giedd. He continues thus, “If young teens are emotionally propelled by the limbic system, yet prefrontal control is not as good as it is going to get until, say, age 25, that leaves a decade of time during which imbalances between emotional and contemplative thinking can reign.” It is within this gap or mismatch that we find “increased risk taking and sensation seeking” (quoting Dr. Giedd). Yeow! Dr. Giedd suggests that this mismatch could “pose substantial dangers, especially when mixed with modern temptations such as easy access to drugs, firearms and high-speed motor vehicles, unchecked by sound judgement.” But, wait, there’s a problem here, one we have talked about in the previous post.

If EF does not come online until the late teens or early 20s then why are the Yeagers talking about developing executive function skills like impulse control and planning in children ages four to eleven? Or why has neurobiology and attachment researcher Allan Schore spent his entire career studying the development of affect regulation in mother-infant pairs if the limbic system comes online with puberty? Hmmm? Once again I think we can find the answer by looking at Executive Function development as existing on a continuum with individual skills (or orchestra members) on one end and PFC orchestration on the other. I think it’s a potentially dangerous message to suggest that EF only appears in the late teens or early 20s. Let me dive into this a bit deeper because I think it’s an important point.

Here’s how Dr. Giedd describes a very important feature of the prefrontal cortex called “running what-if scenarios.”

An important feature of the prefrontal cortex is the ability to create hypothetical what-ifs by mental time travel—to consider past, present and possible future outcomes by running simulations in our mind instead of subjecting ourselves to potential dangerous reality. … As we mature cognitively, our executive functioning also makes us more likely to choose larger, long-term rewards over smaller, short-term ones.

Without realizing it (I’m assuming) Dr. Giedd just described high delaying behavior as observed through the Marshmallow Test. And I would suggest that running what-if scenarios involves orchestrating several EF skills such as mental time travel and perspective-taking. The point being that the PFC cannot orchestrate executive function skills to, say, run what-if scenarios, if those skills are not already in place in some form. Now I’d like to get into a bit of speculation.

Dr. Giedd spends time looking at the process of brain myelination. On a very general level the brain is comprised of both gray matter and white matter. “The ‘white’ in white matter comes from a fatty substance called myelin, which wraps and insulates the long wire, or axon, that extends from a neuron’s body,” reveals Dr. Giedd. He continues, “Myelination—the formation of this fatty sheath—takes place from childhood through adulthood and significantly speeds up the conduction of nerve impulses among neurons.” Here’s Dr. Giedd’s bottom line: “Myelinated axons transmit signals up to 100 times faster than unmyelinated ones.” So, it’s not enough to have signals racing through one’s brain. If you wish to “save” a particular pathway then it’s a good idea to get it myelinated. There’s a definite “use it or lose it” aspect to this “feast or famine” process. Again, unused connections or pathways could be pruned during a process of selective elimination. OK, I’m going to go out on a limb here but is it possible that there’s such a thing as “social myelination,” using society to in essence “sheath” or protect the developing brain as it develops actual myelination? Let me argue this from the opposite direction.

We know from the many attachment studies that have been done on infants and children raised in Romanian orphanages that they often develop what researchers call “disorganized attachment.”(2) Disorganized attachment later in life can often result in disordered thinking processes characterized by an inability to regulate affect. Suffice it to say that neglect of this kind could push a person toward the psychosis threshold. Sadly, there is a connection between disorganized attachment and borderline personality disorder. Researchers point to an overabundance of stress hormones, like cortisol, as the main culprit here. Regardless, these developing brains are being sculpted by the environment. Sure, evolution has developed the “feast or famine” or “use it or lose it” processes, but society to a large extent says how much feast, how much famine, what is used, or what is lost. Again as I suggest above, maybe high delayer behavior implies a “nutrient rich environment.” And I think Dr. Giedd gets all of this when he says

Adolescents’ inherent capacity to adapt raises questions about the impact of one of the biggest environmental changes in history: the digital revolution. Computers, video games, cell phones and apps have in the past 20 years [now almost 30 years] profoundly affected the ways teens learn, play and interact. … The skill of the future will not be to remember facts but to critically evaluate a vast expanse of data, to discern signal from noise, to synthesize content and to apply that synthesis to real-world problems.

I agree with Dr. Giedd’s assessment here. However, consider what all goes into making up this skill of the future: 1) critical evaluation, 2) an ability to model a vast expanse of data, 3) to discern signal from noise (or, as mentioned in the previous post, filter out extraneous information), 4) to synthesize content, and 5) apply synthesis to real-world problems. Dr. Giedd has described an exceptionally high level of Executive Function brought about by an exceptionally high level of EF skill orchestration. At the risk of being glib, Dr. Giedd has described himself, a scientist with years of advanced training and experience. In contrast we now find ourselves within an increasingly postmodern environment that takes a dim view of science. This is not an environment within which Dr. Giedd’s skill of the future can flourish.

Over the time horizon of evolution we are provided with a camera of sorts in the form of various arrays of neurons and synapses. Over the time horizon of an organism’s lifespan, that organism takes a time-lapse picture of their environment. This picture hopefully allows the organism to better navigate the environment. If all goes well and that organism meets up with a positive and supportive environment then the resulting picture could be rather rosy. A depleted environment could result in a picture (or brain organization) that puts one at risk of dropping below the psychosis threshold as often happens with Romanian orphans. Children, teens, and many adults are taking “brain-development pictures” as it were and showing them to us. These are pictures of our environment shown to us through behavior. Fortunately as the work of the Yeagers points out, these pictures can be changed. I would suggest that there is a limit to the brain’s plasticity. Insults to the brain such as PTSD (post-traumatic stress disorder) are exceedingly hard to treat. Maybe the current desire to take selfies is a sign saying, “Look at the pictures that are us. They are telling you something. Look at them.” Do we provide social myelination, social scaffolding, or do we allow brains to develop willy nilly? Dr. Giedd talks about the mismatch between the limbic system and the PFC. As I see it the need for social scaffolding is going up as the supply of social scaffolding is going down. This mismatch only pushes us closer to the threshold of psychosis. Just saying.


(1) Developmental Disruptions In Neural Connectivity In the Pathophysiology of Schizophrenia by K.H. Karlsgodt et al. in the February 2008 issue of Development and Psychopathology.

(2) See the work of Charles Zeanah for more on this subject. Dr. Zeanah teaches at Tulane University in the psychiatry department and has spent considerable time studying the attachment patterns displayed by Romanian orphans.