Biology of ADHD

Posted by on May 10, 2016 in Attention/ADHD | 0 comments

Last week we met “Ryan.”


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Read more about “Ryan” here


“Ryan” is a case of classic ADHD with hyperactivity if we were to use the standard labels. In review, he had the core ADHD symptoms of inattention, distractibility, disorganization, hyperactivity, restlessness, and impulsivity. But is this just his personality? Is this just how he is built? And if he is “built” this way, is this necessarily a problem? Do we need to do anything about it? And if so, do we need to do it now?

Let’s take a look at some of the biology of ADHD.

Biology of ADHD

What do we see when we look into the biology of ADHD? In this post and the next we will explore findings from brain imaging, studies of neurotransmitter systems, and genetics.

Lets start by looking at some of the brain findings.

Many studies have been done comparing the brains of children diagnosed with ADHD (agreeably a very heterogenous group) with non-ADHD controls. In general, children with ADHD tend to have smaller cortical volumes in the frontal cortex when studied with MRI (magnetic resonance imagery). This matches many of the symptoms we see. The frontal cortex — particularly the prefrontal cortex — is involved with executive function and higher aspects of self-regulation and attention. But it is important to stress that these are only averages. Not every kid with ADHD is going to have smaller frontal areas, and not every “normal” child will have larger volumes. Put another way, this is no way to diagnose ADHD.

Other areas found to be commonly abnormal on MRI are the basal ganglia, cerebellum, and sometimes the parietal lobe. These findings are less consistent than frontal cortex abnormalities, but are common enough that they probably tell us something about at least a subset of affected individuals.

One interesting study followed children with ADHD over time. What they found was that the smaller frontal cortical volumes seen in the beginning was only temporary. Over time, the size of the frontal cortices of the children with symptoms did catch up to the non-affected children. At least in some cases, ADHD symptoms may reflect a delay in brain maturity rather than a permanent set of deficits.


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Decreased activity in the prefrontal areas in ADHD
(SPECT scan done at Amen Clinics)


Another mode of brain imaging is SPECT (single photon emission computed topography) scans where the brain’s activity levels and blood flow are measured in real time. Dr. Daniel Amen has done ~ 20,000 scans on people with ADHD symptoms over the last 25 years. He has found people with classic ADHD symptoms to show scans that generally match those described above. During SPECT scans these kids generally show healthy brain activity at rest. But during concentration tasks, there tends to be decreased blood flow in the underside of the prefrontal cortex (PFC), cerebellum, and the basal ganglia.

I would again stress that this is not how we decide if someone has ADHD. The traditional way is to use a symptom scoring system like the Conners or Vanderbilt and also ascertain if the symptoms are impairing the child’s quality of life. But for many people, it is really helpful to see a tangible reason for why they are having challenges with things that others do much more easily. And in the case of SPECT scans, you are looking at your brain in real time.

Another set of findings involves looking at the patterns of electricity running through the brain with EEG (electroencephalography). Children with classic ADHD tend to show abnormally high levels of alpha and theta waves at rest. At the same time, these children show lower levels of beta waves at 13-21 hz. Alpha waves are 8-12 hertz (hz) and tend to be associated with states of relaxed alertness, especially when our eyes are closed. Theta waves are 3-7 hz and are prominent when we are somewhat drowsy and/or “tuned inward.”  Beta waves are associated with focused, sustained attention and problem solving. Again, the biology of ADHD makes total sense with what we see behaviorally.


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Color graphic of EEG findings in ADHD


One amazing finding is that one can predict ADHD symptoms with 80-90% accuracy based on the ratio of theta to beta waves. That is pretty impressive. And just as amazing is the fact that many children can be taught to increase their beta wave activity when necessary through EEG neurofeedback. What does this tell us? Firstly, we are never mere slaves to our biology. And second, there are ways to shape biology other than pharmaceuticals.

One other fact I will note is that a small minority of children have a different EEG pattern – that of over-expression of beta waves. This probably correlates to other types of ADHD in Dr. Amen’s system and require a different set of interventions. We will discuss this type in later posts.

Now I would agree that all of this does not prove that ADHD is a purely biological disease. We know that our environment can powerfully change how our brain functions in the moment and grows over time. But I think it is quite obvious that we all have different strengths and weaknesses, and that many of these are rooted in our biology. Said a different way:

Even though ADHD is way over-diagnosed, and there is an entire industry built around manufacturing as many diagnoses as possible and selling their “miracle” drugs to the afflicted, there is still something real here that often requires extra support.

What kind of support is my current area of passionate exploration.

Next week I will continue to describe the biology of ADHD by turning towards genetics and the neurotransmitter systems involved.


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Chris White MD

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