Early Toxic Stress Changes Brain Structure

ADHD research needs to take stress into account.

Posted May 07, 2018

I beg to differ with Dr. Rettew's conclusion that the new study he cites "proves" that ADHD is real. The study Dr. Rettew cites leaves out a significant factor in children's brain development: namely, the study fails to recognize the degree to which very early exposure to stressful experiences and environments can affect the architecture of the child's developing brain. That is, factors in the young child's environment can change the size of the child's brain.

There are many studies that support the conclusion that experience changes the brain. See, for example, a working paper from Harvard University's Center on the Developing Child "Excessive Stress Disrupts the Architecture of the Developing Brain."

This study points out that "the neural circuits for dealing with stress are particularly malleable (or “plastic”) during the fetal and early childhood periods. Early experiences shape how readily these circuits are activated and how well they can be contained and turned off. Toxic stress during this early period can affect developing brain circuits."  

Stress mobilizes hormones like cortisol and adrenaline in the child. "Sustained or frequent activation of the hormonal systems that respond to stress can have serious developmental consequences, some of which may last well past the time of stress exposure. When children experience toxic stress, their cortisol levels remain elevated for prolonged periods of time. Both animal and human studies show that long-term elevations in cortisol levels can alter the function of a number of neural systems, suppress the immune response, and even change the architecture of regions in the brain that are essential for learning and memory."

There are myriad  studies that show how environmental factors like stress play a major part in children's brain development. To name only two: Lupien, S. J., de Leon, M. J., de Santi, S., Convit, A., Tarshish, C., Nair, N. P. V., … & Meaney, M. J. (1998). Cortisol levels during human aging predict hippocampal atrophy and memory deficits. Nature Neuroscience, 1(1), 69-73, and Lupien, S. J., McEwen, B. S., Gunnar, M. R., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behavior and cognition. Nature Reviews Neuroscience, 10, 434-445.

According to the study cited, participants were excluded if they had a "history of physical, sexual, or emotional abuse" based on their medical history. So the researchers did recognize that environmental factors play a role in brain architecture or that symptoms of abuse may be misdiagnosed as ADHD. However, here are three points to be made about this attempt to exclude participants on the basis of abuse.

First, parents don't always report that they have abused or neglected their children and children are usually too scared to report it themselves. 

Second, the abuse may have occurred without the parents' knowledge (by a family member, family friend, babysitter or nanny). As a practicing therapist, I know this latter type of abuse occurs much more frequently than one would think.

 Third, there are forms of excessive stress on a young child that do not fall into the category of physical, sexual or emotional abuse. Examples of severe stress that may impact a child's developing brain are: 1) witnessing domestic violence or chronic parental fighting, 2) the child being bullied, 3) economic hardship, 4) excessive exposure to electronic screens (see, for example, psychiatrist Victoria Dunckley's Psychology Today blogs on how excessive screen time can change neural circuits). It is reasonable to conclude that at least some of the children in the study had been exposed to forms of environmental stress that were not accounted for. 

Dr. Rettew seems to believe that the study he cites is a "magic bullet" that will put to rest once and for all the view that ADHD is based on a genetic or brain defect. This is clearly not the case. Nor is it the case that those of us who are skeptical that ADHD is a real  "disease" need to "spin" studies with conclusions we do not agree with.

We skeptics do not have an ax to grind. We are open-minded to all the evidence, which biologically inclined psychiatrists are unfortunately not apt to be.  New evidence of severe stress on children's brains emerges every day. Who would have thought that parents would put an infant on a swing in front of a television set for 4-6 hours a day or let toddlers play video games for hours on end. This electronic over-stimulation puts enormous stress on young children's brains and, yes, it can cause neurological changes. 

Whichever narrative we accept, whatever studies we emphasize to support our views, I suggest we keep the discourse civil. Most of us in the field of child development are interested in the true well-being of children and not at looking at how we can "spin" a study we don't agree with. 

References

Lupien, S. J., de Leon, M. J., de Santi, S., Convit, A., Tarshish, C., Nair, N. P. V., … & Meaney, M. J. (1998). Cortisol levels during human aging predict hippocampal atrophy and memory deficits. Nature Neuroscience, 1(1), 69-73.

Lupien, S. J., McEwen, B. S., Gunnar, M. R., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behaviour and cognition. Nature Reviews Neuroscience, 10, 434-445

 National Scientific Council on the Developing Child. Working paper 3. Excessive Stress Disrupts the architecture of the Developing Brain.