Pruning, Myelination, and the Remodeling Adolescent Brain

It’s not so easy being an adolescent these days. We become aware of the world around us, are flooded with input through digital media about our extended global family, and learn about the world’s intense and overwhelming problems. And even more, puberty’s onset is getting earlier, and the time between our childhood dependence and adult responsibility over the last century has moved from a couple of years to a dozen or more.

In my own family life, our two children have now passed through their teenage years. But recent studies of the brain, done at UCLA, the National Institute of Mental Health, and other research institutions, reveal that their adolescence is not over. Longitudinal investigations of individuals going through the period between childhood and adulthood reveal that there is a remodeling of the brain that starts often just before the teen years begin and continues well into the mid-twenties.

For adolescents, this means that the pruning down of existing neurons and the laying down of myelin sheaths connecting the remaining linked neurons will continue years after we stop referring to them as “teenagers”.

But what is this remodeling all about? Why would nature provide for the rewiring of a brain such that there is the purposeful, genetically governed, and experientially shaped destruction of existing neurons and their synaptic connections?

Pruning means that the abundance of neural connections achieved during the sponge-like soaking in of knowledge during the childhood period will be whittled down, shaped like a garden. What was surprising to many was that such a pruning process would be so robust, a process that can be intensified with stress.

And it is this pruning process that may explain the finding that most of the major psychiatric disorders—of thought, mood, and anxiety—have their major onset during this vulnerable period. Pruning may reveal genetically or experientially vulnerable circuits.

The classic “use it or lose it” principle applies to adolescence—those circuits that are actively engaged may remain, those underutilized may be subject to systematic destruction. And so for an adolescent, this means that if you want to learn a foreign language well, play a musical instrument, or be proficient at a sport, engaging in those activities before and during adolescence would be a good idea. We move from open potential in childhood to specialization during and following adolescence.

And the myelination of the remodeling brain? Myelin enables the remaining and connected neurons to communicate with each other with more coordination and speed. Myelin permits the action potential—the ions flowing in and out of the membrane creating a flow of charge down the long axonal length—to move one hundred times faster. And the resting time between firings, the refractory period, is thirty times quicker. That means neural firing becomes three thousand times quicker with myelination. When you notice that those Olympic athletes are doing feats you could only dream of doing, you are not exaggerating. Practice lays down myelin to enable a skill.

In a field I work in called interpersonal neurobiology, we attempt to bring together all of the fields of science, and other disciplined ways of exploring reality as well such as art, music, literature, and contemplative practice, into one conceptual framework. In that view, we see a process called “integration”—the linkage of differentiated parts of a system—as the mechanism beneath health. With integration, harmony is created.

When linkage and differentiation are not present, chaos and rigidity can emerge. Integration creates the possibility of regulation—of attention, mood, emotion, thought, social interactions, and behavior. And much recent research supports this notion that impaired integration in the brain is at the root of many psychiatric disturbances.

And so adolescent remodeling with its pruning that creates a more differentiated brain and its myelination that links those differentiated regions is really all about creating more integration.

Naturally a remodeling zone will not be as functional during the re-constructive process as it will be later on: at times we need to shut-down the electricity or the plumbing during the process. But in the long run, the adolescent brain will result in more refined capacities, more emotional balance, more insight and wisdom, all processes resulting from integrative capacities to create internal well-being and interpersonal health.

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INSPIRE TO REWIRE is a mark owned by Dr. Daniel J. Siegel and Mind Your Brain, Inc. All rights reserved.