While reading a 2007 press release from the National Institute of Mental Health (NIMH), I became unusually hopeful for youths diagnosed with attention deficit hyperactivity disorder (ADHD). A study performed jointly by the NIMH and the National Institute of Health revealed the brains of youths with ADHD develop normally but at different rates. In the prefrontal cortex, development was delayed three years on average in youths diagnosed with ADHD. This region of the brain is associated with higher-order executive functions and is responsible for coordinating actions with thoughts according to a person’s goals and intentions.
But while development of the prefrontal cortex lags in youths with ADHD, the motor cortex, which controls voluntary body movement, matures faster. These combined changes correlate with behaviors seen with ADHD: fidgety, restless bodies that have difficulty inhibiting behavior and focusing attention. These behaviors impact their ability to do well in reward-based systems that require delaying gratification while working towards long-term goals (that is to say, school).
Much can be gleaned from this study about the causes of ADHD as well as best treatments. Here, I thought, was evidence that implied ADHD was as much influenced by environmental conditions as yet-to-be-determined genetic markers. But then I read the NIMH press release's conclusion:
“In future studies, the researchers hope to find genetic underpinnings of the delay and ways of boosting processes of recovery from the disorder.”
I was dismayed. Granted, the study dates back to 2007, but so does evidence about the relationship between ADHD-like symptoms and exposure to trauma, particularly in children who have been either physically or sexually abused, or both. In one study of sexually abused girls, 28 percent met diagnostic criteria for ADHD — compared to only 4 percent of the subjects in the non-traumatized control group. The impact of combined sexual and physical abuse is even more startling. In another study (cited in a presentation by psychiatrist Bessel van der Kolk for the National Child Traumatic Stress Network), 67 percent of boys with histories of both physical and sexual abuse displayed the symptoms for ADHD. In this study, 40 percent of boys with histories of sexual abuse only and 36 percent of boys with histories of physical abuse only also met the criteria for ADHD.
Changes in brain development have both genetic and environmental origins. At birth, the human brain is grossly underdeveloped. It takes as much as twenty years to reach full maturity (some say longer), increasing in size by more than 300 percent during its development. Throughout this maturation process, the brain’s developmental path is modulated by experience. Genetic programming guides the process, but appropriate and expected responses from the environment keep development on track. And of course, childhood abuse is not one of these appropriate and expected responses.
David J Linden, a professor of neuroscience at John Hopkins University School of Medicine and author of The Accidental Mind, gave the following explanation of the interaction between genes and the environment in the development of the human brain:
“although the overall size and shape of the brain and the large-scale pattern of connections between brain regions and cell types are instructed by genes, the cell-by-cell details are not. The precise specification and wiring of the brain depends upon factors not encoded in the genes (called epigenetic factors), including the effects of the environment” [p. 52].
Furthermore, the impact of the environment can be profound enough to alter how genes function. Quoting Linden:
“in the past, there has been a tendency to imagine that genes and behavior interact in only one direction: genes influence behavior. We now know that the environment, broadly considered, can also influence gene function in brain cells. In other words, nurture can influence nature and vice versa. Causality, in the brain, is a two-way street” [p. 55].
Like the scientists at the NIMH, trauma-focused researchers are concerned with the relationship between mental disorders and brain development. However, they look at the environment’s contribution to mental disorders rather than focusing on genetic influences. For example, researchers working with children exposed to traumatizing events have identified a list of difficulties children often have after being exposed to traumas such as chronic physical or sexual abuse. These include: difficulty controlling emotions, problems concentrating, difficulty with impulse control, and aggressive or risk-taking behaviors — all symptoms of ADHD. Some trauma-focused researchers, including van der Kolk, have suggested adding a new diagnosis to the Diagnostic and Statistical Manual of Mental Disorders — “Developmental Trauma Disorder” — that would include addressing ADHD-like symptoms from a trauma-informed perspective. Rather than waiting for elusive “genetic underpinnings,” this disorder would point directly to what often causes ADHD-like symptoms: multiple or chronic exposure to one or more forms of interpersonal trauma — and childhood abuse is a primary type.
Does trauma-focused research imply all children diagnosed with ADHD have been abused? Certainly not. But such research should persuade institutions like the NIMH to exercise their ethical responsibility and encourage mental health professionals to consider childhood abuse as the reason for ADHD-like symptoms — and well before prescribing medications, particularly when intervention in the child’s environment is most needed.
© 2013 Laura K Kerr, PhD. All rights reserved (applies to writing and photography).
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