A new study published in a prestigious medical journal attempts to shed new light on an old question, namely the neurobiological underpinnings of ADHD. As can be readily seen by bloggers on this website along with many others, the diagnosis of ADHD remains quite controversial. Even among those inclined to support the legitimacy of the diagnosis, greater clarity regarding what is actually happening in the brain in those struggling with ADHD symptoms is sorely needed.
The study represents a nice example of the new generation of brain imaging studies that focus less on the size or activity of a particular brain region in isolation and more on regional networks of several areas that are functionally connected to each other when the brain is doing tasks or at rest. Perhaps the most famous of these networks relates to brain activity when we really aren’t doing anything. This has been known best as the default mode network or DMN.
MRI scans from a group of 135 individuals with a diagnosis of ADHD were compared to 188 typically developing controls from ages 7 to 21. To compare activity in various brain networks, the authors employed complex analyses called whole-brain connectomic methods that allowed the authors to examine more than 400,000 different brain connections.
In terms of results, maturation lags were found among those with ADHD, particularly within the default mode network and between the DMN and two other “task positive” networks (those networks involved in specific cognitive functions), namely the frontoparietal and ventral attention network (VAN). The VAN is involved in salience processing, i.e. detecting the relevant stimuli in the external environment while the frontoparietal network is involved in adaptive cognitive control. The implication of both of these networks in ADHD makes intuitive sense and provides ever more increasing and specific evidence that the challenges related to ADHD reflect "real" alterations in brain function and structure.
At the same time, the hypothesis of ADHD as brain maturation delay could offer a compromise between those inclined to dismiss the very existence of ADHD and those who view it from a more traditional disease model. Before getting too excited, however, I personally would like to see more evidence regarding whether the brain function of those diagnosed with ADHD eventually catches up or whether these differences persist later in life. As far as I can tell, this study does not address this important point. Clinically, many people do seem to “outgrow” childhood ADHD struggles, many don’t, and others design their life in a way so as to minimize the impact of them.
Furthermore, it’s not always clear what people mean by the word “delay.” To many, a delay means that eventually things will get there, as in, “My train is temporarily delayed.” When it comes to child development, however, the term unfortunately is often used without such reassurances implied. As far as this study goes, it seems as though the term delay really just meant that how well these networks functioned was related to both to age and whether or not one was diagnosed with ADHD.
In the end, this is certainly an important study, with pieces that can be used to bolster those on both sides of the ADHD debate.
Image courtesy of dream designs and freedigitalphotos.net
@copyright by David Rettew, MD
David Rettew is author of Child Temperament: New Thinking About the Boundary Between Traits and Illnessand a child psychiatrist in the psychiatry and pediatrics departments at the University of Vermont College of Medicine.
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