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ADHD Is Real: Brain Differences in Preschool-Age Children

A new study provides more evidence for the neurobiological basis of ADHD.

ADHD remains a controversial diagnosis to a skeptical core of people who continue to question its biological validity. Sure, there are tons of studies that provide strong evidence of genetic and brain differences related to ADHD, but many of these studies are able to be dismissed because one can argue that it is the toxic effects of medications that are driving any neurobiological differences, or that the authors are corrupted by ties to pharmaceutical companies.

Enter a recently published and government-funded study that looked at brain volume differences between a group of young 4- to 5-year-old children with ADHD who have never been exposed to ADHD medications and a group of typically developing controls. The two groups were also matched according to IQ and language function to minimize other potential group differences.

Results showed that children with ADHD had significantly smaller overall cortex volumes (about 5 percent smaller in terms of absolute differences) and these differences were most prominent in many specific brain regions that are known to be involved in processes that are difficult for children with ADHD, such as inhibiting one's actions or reducing distractions.

All told, this is one of the first studies to show such broad-based brain volume differences in subjects this young who had never taken medication. And while widespread brain volume differences are hardly a smoking gun regarding exactly what is happening neurodevelopmentally with ADHD, the data argue quite strongly that there do exist real brain-based differences that are evident at an early age.

It will be interesting to see how those who enjoy bashing psychiatry and denying ADHD will spin this study. So far, the strategy seems to be to ignore it altogether and hope that people don’t notice. This may not be a bad idea for those who would like to dismiss ADHD as an entity made up by drug companies to sell medications, or as a pathologizing of kids who are slightly younger than their classmates in school. For these folks, there are some inconvenient aspects to this study, including the following:

  1. None of the children diagnosed with ADHD were taking medication.
  2. The ADHD group had nearly identical ages and IQs as their comparison group.
  3. The study was funded by the NIH and none of the authors had any ties to any pharmaceutical company.

To be fair, this study does not try to argue that misdiagnosis can’t happen with ADHD or that there do not exist kids who are being given medications who don’t need them. There are legitimate reasons that ADHD is more debatable than some other medical conditions and a previous post describes this in more detail. Nevertheless, this study is one of many that is starting to make it exceedingly difficult to categorically write off the scientific validity of ADHD without undertaking some Olympic-level intellectual gymnastics.

Some Comments About the Response to This Post

You will see that a response to this post has been written by Dr. Marilyn Wedge. I am happy with her willingness to engage in this discussion and encourage you to read her response. In it, she expresses disappointment with my claim that people will try to "spin" the results of this study, but when someone quotes you as using words you didn't write and then tries to invalidate the study's data by claiming that parents of ADHD children either lied or were unaware of their children's past trauma, that is kind of textbook spinning in my book.

The main point of discussion, however, should be Dr. Wedge's central premise that early trauma is what drives ADHD behaviors, and therefore the diagnosis of ADHD in invalid. She cites a number of studies demonstrating that trauma and early experience have profound effects on a developing brain. I couldn't agree more, as you can read in previous posts I have written such as "Nature Versus Nurture" and "ADHD and Trauma." You can also add lead toxicity and traumatic brain injury to the list of environmental factors that can cause or exacerbate ADHD symptoms.

What seems odd to me, however, is that I would think that such evidence about the power of the environment would serve to bolster the legitimacy of ADHD, not weaken it. Some children arrive at having ADHD behaviors through genetic mechanisms, others through environmental ones, and most through a combination of the two. The end result, however, is a brain that is developmentally different, as described in this study.

Perhaps the issue is really about medications, which certainly can be overused, as I have written about in other posts. Dr. Wedge and I would probably agree that the use of medication while ignoring trauma that is making behaviors worse is inappropriate. Where we probably differ, however, is my view that judicious use of medications should not depend on the pathway we believe someone took to get to the place they are today.

Consider two people who broke their legs, one because of genetic effects that made the leg weak, while the other person got hit by a bus. The end result is two people with broken legs, both of whom are in pain, and both of whom need help.


Jacobson LA, Crocetti D, et al. Anomalous Brain Development Is Evident in Preschoolers With Attention-Deficit/Hyperactivity Disorder. Journal of the International Neuropsychological Society (2018); 24;1–9.

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