Childhood Stress, Brain Pruning, and Adolescence

Creative Human Brain

The more we learn about the brain and trauma, the more we can all share in a profound appreciation for the complexity and sophistication of how it develops and changes over time. Also, the deeper our appreciation can be for its potential to be destructive for brain growth and development, both in the short and long-term.

In rereading Childhood Disrupted: How Your Biography Becomes Your Biology, and How You Can Healby Donna Jackson Nakazawa, she describes a perfect storm as the chilling result of childhood stress blended with normal brain pruning that occurs during adolescence. This provides an explanation for the behaviors of teens who experienced childhood adversity. It can be an enormous motivator to advocate for whatever can prevent or intervene when children are in potentially traumatizing situations or relationships.
young school girl with backpack

When children come into adolescence, they naturally undergo a period of developmental pruning of neurons. When we are very young, we have an overpopulation of neurons and synaptic connections. Some of them die off naturally to allow us to ‘turn down the noise in the brain,’ says McCarthy [a PhD Professor of Neuroscience at the University of Maryland School of Medicine], and to increase our mastery and skills that interest us. The brain prepares for becoming more specialized at the things we’re good at and interested in, while we lose what we don’t need.

But if, due to childhood stress, lots of neurons and synapses have already been pruned away, then when the natural pruning that occurs during adolescence begins to take place, and the brain starts to naturally prune neurons it doesn’t need so that a teenager can focus on building particular skills–baseball, singing, poetry–then, suddenly, there may be too much pruning going on.

Brain therapy and mental health treatment concept as a sheet of torn crumpled white paper taped together shaped as a side profile of a human face

Dan Siegel, M.D., child neuropsychiatrist and clinical professor at the University of California, Los Angeles (UCLA), is the pioneer of a growing field known as ‘interpersonal biology,’ which integrates the fields of neuroscience and psychology. According to Siegel, “the stress of Adverse Childhood Experiences causes toxicity in the neurons in the neural pathways that integrate different areas of the brain. When adolescent pruning occurs in the integrated circuitry between hippocampus, which is important in storing memories; the corpus callosum, which links the left and right hemispheres of the brain; in the prefrontal cortex, these change,” says Siegel, “and have a profound effect on our decision-making abilities, self-regulatory processes, attention, emotional regulation, thoughts, and behavior.”

“When these integrated circuits are affected by adversity, or genetic vulnerability, or both, during preadolescence,” says Siegel, “and then puberty hits,’ adolescent pruning pairs down the existing but insufficient number of integrated fibers, which makes a child vulnerable to mood dysregulation. It is when this brain integration is impaired that a dysfunction in mood regulation may emerge.’”

Nakagawa goes on to share a hypothetical image. She asks us to imagine that all children start with 4000 neurons, which is a concocted number just to illustrate her point. If there were two healthy five-year-old boys, Sam and Joe, and Sam experienced early adversity and Joe did not, Sam’s neurons would be slowly pruned away. By the time Sam was 12, after a lot of this stress-related neuronal pruning, he would end up with 1800 neurons, which still allows him to function. But when he and Sam go through adolescence with all its neuronal pruning, both Sam and Joe lose a hypothetical 1000 more neurons. Now Sam, who grew up with all that chronic, unpredictable stress is going to have a totally different brain from Joe. Joe, still has his 3000 neurons while Sam is left with only 800 neurons, meaning Sam does not have enough neurons for his brain to function in a healthy manner.

Siegel explains, “For kids who have already had pruning due to early stress, when average adolescent pruning occurs, what remains may be insufficient for mood to be kept in balance. If stressors are high, this pruning process may be even more intense, and more of the at-risk circuits may be diminished in number and effectiveness.”

ACEs word cloud

He adds, “The child who faces Adverse Childhood Experiences will be more likely to develop depression, bipolar disorder, eating disorders, anxiety disorders, poor executive function in decision-making–many of which can lead to substance abuse. This may be why, statistically, so many young people first show signs of depression or bipolar disorders in high school, and in college–even kids who just a year or two earlier seemed absolutely fine.”

This is sobering information for all of us, a reminder of the amazing complexity of the brain and the potential for trauma to be extremely destructive to a brain, especially during adolescence. In my next blog I’ll share some neurobiological information that can allow us to feel hopeful. For now, I think appreciating the impact of trauma and its potential for long-range damage is something important for all of us to know.

Invitation to Reflect:

  1. How does this information help you better understand the nature of the brain and the impact of stress on the developing brain?
  2. How does it help you better understand some of what happens during adolescence?
  3. What images come to mind when you think about what might be going on during all the pruning that happens to a young person with some kind of trauma history? Does this young person show any of the symptoms described by Nakazawa?
  4. What are your thoughts about finding ways to help others appreciate this information in the hope that they might be willing to be more of an advocate for healthier parenting and the caregiving of all children?

Diane Wagenhals, Program Director, Lakeside Global Institute