What causes ADHD?

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Why does a kid suffer from Attention Deficit Hyperactivity Disorder (ADHD)? Are the pathological symptoms acquired or inherited, and can we shut them down?

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Searching for the cause(s) of a mental disorder is like looking for a needle in a haystack. There can be multiple causes to the disease which take place at different levels of biology (both within and beyond the brain). Each level of investigation can provide its own level of understanding but none of them are sufficient to determine whether someone has a mental disorder.  Let’s take the example of ADHD.

Finding mental disorders in brain scans
One of the most common methods for studying the brain is functional Magnetic Resonance Imaging (fMRI).  Does this mean that we can observe signs of ADHD from fMRI derived images of brain activity? In 2011, the ‘ADHD-200’ competition was held in order to try to answer this question.

In this competition, contenders had to build an algorithm to identify ADHD based on fMRI data. Ironically, the team who won the competition ignored all the provided imaging data. Instead they classified patients simply on the basis of demographic information, such as age and gender. This raised the question as to whether there are any anatomical or functional features in the brain that could serve the diagnosis of ADHD.  Should we be looking elsewhere for signs of ADHD?

Heritability
What about looking at genes instead of brain activity? After all, studies show that the diagnosis of a parent with ADHD is a highly predictable factor of their child having ADHD, which suggests that ADHD is highly heritable. Literature on the genetic causes of ADHD is broad and points to multiple candidate genes associated with the neurotransmitter dopamine. However, these studies have been hard to replicate, and thus far, no gene has been acknowledged to be associated with ADHD.

Does ADHD even exist?
But… Wait a minute! Could it be that distractibility and poor attention are just regular personal traits, and that ADHD does not exist at all? This is a controversial subject, and it was recently addressed in the book ADHD Does Not Exist: The Truth About Attention Deficit and Hyperactivity Disorder by the American neurologist Richard Saul. In Saul’s opinion, ADHD is not a standalone disorder but rather a combination of twenty different symptoms.

Another popular opinion is that ADHD is not a disability but a useful trait . Diffuse attention and a tendency for exploration can be very advantageous in evolution, which could explain why the ‘disorder’ is so common. This explanation also explains why the difficulty we have in capturing the signatures of ADHD in the brain and in the genome.

Future of ADHD research
Nevertheless, millions of people worldwide declare that they suffer from distractibility and poor attention, which suggest it is an important issue to address. To help tackle this issue, Radboud University hosts multiple research projects devoted to ADHD. By studying the disorder across many levels, from brain scans to the doctor’s office, we hope to find new ways to predict, diagnose and treat ADHD.

More information
General introduction to ADHD
Website of the NeuroIMAGE project, Radboud University’s ADHD research initiative

This blog was written by Natalia Bielczyk. Natalia is PhD student in computational neuroscience at the Radboud University Medical Center. She works in the Translational Psychiatry lab, where she investigates brain mechanisms underlying cognitive disabilities, especially of the attention deficit kind.

Edited by Jeroen.

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