Why we're "complicated" from 12 to 30...recent research

A major development in cognitive neuroscience and neuroplasticity in the last 10 years is a better understanding of why we behave in the "complicated" ways we do during our teens and into our late 20s.

There are many jokes about this "interesting" 12 to 30 years old (12-30) period, including "'Teen Brain' is an oxymoron", and "It is important to remember that teens' brains are controlled from another planet".

The brain during 12-30 is not an old child's brain, nor is it an improperly-functioning adult brain.  This is a major developmental period during which dramatic adaptive changes are made in the connections between different regions and in neural architecture.  These prepare the functional capabilities and skills needed for the environment it will be functioning in for many decades.

Earlier blogposts "How the brain continually changes and reorganizes itself", "Our constantly changing brain...", "How the changeable brain fixes/causes learning disabilities...", etc., highlighted the advances in the understanding of neuroplasticity - the ability of the brain to reconfigure itself to adapt to changing demands, including socialization, intellectual and functional requirements throughout life, which is particularly critical during 12-30.

Timing mismatch between
development of emotion
and control regions
(Scientific American)

A consequence of maintaining this "flexibility" to shape the brain for adaptation to changing environments, is the different rate at which different parts of the brain are "defined".

The limbic system, which manifests our emotions, behaviors, motivation, emotional memory, etc., manifests strongly at puberty (which is getting younger, world-wide).   These behaviors for the 12-30s increasingly include risk-taking to understand new environments, exploring new sensations and skills, and decreased reliance on parents in favor of peers who will become increasingly important.

These are natural components of learning how to operate successfully in the new, more complex, and socially-connected world where they will soon find themselves "on their own".

However, the typical "balancing" system to these behaviors, emotions, etc., is the prefrontal cortex, which does the planning, problem solving and controlling functions and which doesn't fully develop until about 10 years later.  This timing mismatch is shown in the graphic at left.

There is a great deal of recent research in this area, most notably the paper "Development of Brain Structural Connectivity between ages 12 and 30: A 4-Tesla Diffusion Imaging Study in 439 Adolescents and Adults" by Dennis, et al. in Neuroimage, Vol 64, (2013)".  This paper had a very large statistical population and was carefully conducted by a team from UCLA, Univ. of Queensland, and Univ. of Sydney.   Paul Thompson from UCLA was the lead author, imaging center head and corresponding author.

The focus was on the change in the brain's organizational structure 12-30.  As can be seen in the graphic at right derived from the Dennis, et al. paper for the recent Scientific American article "The Amazing Teen Brain" by Jay Giedd @ UCSD, there is a significant increase in the number of connections between brain regions (larger green circles), and the strength of those connections (darker lines) as the brain adapts to new environments.

The Dennis, et al. paper has two very brief videos showing which centers and connections grow and which centers and connections decline.  The graphic below shows snips from those videos which makes the cross-comparisons easier.

Our species, as has been pointed out in earlier blogposts, has the longest duration of adaptive neuroplasticity.   This allows us to succeed in a staggering range of complex environments from outer space to the South Pole to Maui and from forest to desert to plains and a huge range of different tasks and diets.

Just consider how much we have changed from hunter-gatherers spending most of our time procuring food only 10,000 years ago to today where we spend most of our time on social media, gaming, streaming videos, drinking frappuccinos and worrying.

There are dramatic differences manifesting not only in which centers will be important, but also how densely connected they will be and what the capability is of those connectors.

The capacity and speed of those connectors is controlled largely by what is known as the "white matter", which is the fatty substance called myelin, which surrounds and insulates the "long wire" that extends from each neuron shown at right.

growing myelin for 
faster transmission and firing rates

This fatty coating, which increases in thickness from 12-30, can increase the transmission speed of signals 100X.   It also enables the neurons to recover up to 30X faster after firing, so they can fire more often.

This combination of factors increases communication bandwidth/functionality by a factor of  30 X 100 or 3,000 times, which makes possible more elaborate, complex and useful networks constructed from more distant brain regions.

With these higher speeds and different connection lengths, it is critical to synchronize their actions which also relies heavily on the growing levels of myelin.

Gray matter

While the white matter is growing 12-30, "gray matter", which consists largely of neuronal cell bodies and their projections, and glial cells, which feed, protect and keep the neurons in place, is decreasing.  Gray matter reaches a maximum @ puberty (now 10 years old) and then, as it is "pruned", it declines throughout 12-30 and then levels off.

This pruning of the gray matter is done to remove infrequently used, not useful, or potentially-disruptive neurons and connections.  This same pruning 12-30 is also done on receptors on neurons which activate neurotransmitters like dopamine and serotonin.

Gray matter peaks earliest in areas devoted to sight, sound, smell, taste and touch.   It peaks latest in the areas crucial to executive functioning, organization, decision making, planning and regulation of emotion.  This further exaggerates the timing mismatch between limbic and prefrontal cortex functioning.

Unfortunately, there was no specific focus in Dennis, et al.'s paper on what was happening in the Default Mode Network elements during 12 - 30, i.e. how the "I" network was evolving.  The most significant, strengthening, cross-hemisphere connections all involved the posterior cingulate cortex/precuneus, one of the two key nodes in the DMN.   All connections showed increased fiber density 12-30.  A great deal of work goes on 12-30 on the DMN core.

These huge neural architecture changes manifesting 12-30 are, however, not w/o hazards.  50% of mental illnesses emerge by age 14; 75% by age 24.   Most of the abnormal brain development in adult schizophrenia resembles the typical changes 12-30, gone unchecked.

Professor Paul Thompson,
UCLA
Laboratory of NeuroImaging

It is also the period during which half of the deaths are in motor vehicle accidents, followed by homicide and suicide.

It is a period during which everyone 12-30, and their friends, family, teachers, schools, courts, etc. need to recognize and understand just how huge, and uncoordinated, these brain changes are, and to work with compassion and patience while these brains work out the structure for the rest of their lives.  It is also important to remember that it will be for a world which will be dramatically different from today's.  







                                       
As described earlier, "Into the Stillness: Dialogues on Awakening Beyond Thought", covering Rich Doyle's and my many youTube dialogues on various subjects dealing with nondual awakening, has manifested from Non-Duality Press, a publisher near London.   It can be purchased now from them, and with a week or so from Amazon.