What does brain imaging tell us about ADHD?
Updated: Apr 3, 2021
We now are able to look at the brain in ways that show its development and function. Studies have shown that kids with ADHD have smaller brains than kids without ADHD. This does not correlate with the head size your doctor measures in infancy, and head size does not help physicians predict ADHD.
Last week’s post What is ADHD? Why do some develop it? introduced the concept that ADHD is a brain disorder, not a problem with parenting or other common misbeliefs. Today we’ll go more in depth into how brain imaging has shown differences when people have ADHD. Next week we’ll go further into the genetics of it.
There are many ways we can image the brain for different reasons. Single-photon emission computer tomography (SPECT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI) are all being studied to show different aspects of brain function and development.
Some of the studies look at blood flow to various parts of the brain during different tasks to show which parts of the brain are triggered and how that differences among different groups of people. Others look at subtle changes in brain growth.
With vs without ADHD
Brain imaging comparing large groups of kids with ADHD to those without ADHD show significant differences. These are very subtle differences and are still considered investigational.
The changes are too subtle to diagnose ADHD in any one person.
There are several areas of the brain that have been shown to be smaller in children with ADHD. At this time the specific areas of delayed growth do not correlate with specific treatments.
ADHD is a brain condition
It is not recommended to do imaging studies to diagnose ADHD, but the fact that large groups of people show differences highlights the fact that ADHD is a real disorder of the brain.
Hopefully as this information is recognized, the stigma of ADHD and other brain disorders will be lost. People will be able to understand that it is a real brain dysfunction.
The case for a clinical diagnosis
Studying brain differences helps us to understand ADHD, but imaging is less useful to any individual for diagnosis. We have a good track record for diagnosing ADHD with standardized questions and a clinical history.
Images capture a moment in time, but they don’t necessarily tell the whole story.
What happens to a brain in different circumstances? It can be very insightful to ask what happens when a child is doing a favorite activity versus when he’s stressed.
Clinical history can cover different situations over time. This cannot be captured in any brain image.
To be useful for diagnosis and management of a medical condition, a test must first:
Be reliable: The changes seen are very subtle, and results must be shown to be accessible and identifiable in individuals to be useful for diagnosis. If only a few trained people can identify the subtle differences, it will not be available or helpful to most people.
Show safety: Everything we do in healthcare must be shown to be safe and effective before it’s used. Risks and benefits must be weighed. Risks of imaging must be considered.
Show benefit: If a clinical diagnosis can be made, what benefit would be attained by doing an expensive test? If it does not add to the treatment, it should not be done. Since the large majority of people with ADHD can be diagnosed clinically, we should not need to do studies that add risk and cost.
Back to the prefrontal cortex…
In What is ADHD? Why do some develop it? I mentioned that the prefrontal cortex and said that it was especially interesting. Let’s talk more about why.
Studies have shown that the prefrontal cortex develops more slowly in children and teens with ADHD. This means that the areas of the brain that control executive functioning are thinner in children with ADHD versus those without ADHD.
Functional imaging shows that the frontal lobes in children function less during activities involving concentration, memory, decision-making and problem solving.
It’s even more than that. Those with worse outcomes as they mature have fixed thinning (it doesn’t ever normalize) but those who ultimately develop a normal thickness have a better outcome.
A thinner brain cortex is not a damaged brain. It is an alteration in development.
Other parts of the brain are affected too
Our cerebellum helps us with movement and memory. Children with ADHD show slower growth of cerebellar white matter in early childhood, but faster growth in late childhood.
The amygdala and hippocampus are also smaller in the brains of people with ADHD. These areas are responsible for emotional processing and impulsivity, problem areas for many with ADHD.
What does all of this mean?
You guessed it: it’s still being studied.
Studies continue to help us learn more about brain structure and function. We also continue to learn about the chemical interactions that happen while our brain is working.
What all this information means and how we can use it to best manage the troubling symptoms of ADHD is yet to be fully uncovered.
It may be possible one day to predict which children will develop ADHD and change something in the early years to alter that development. But we’re not there yet…
Does a slower development of certain brain areas have an advantage? Maybe the slower development of the cerebellum is why kids with ADHD learn better when they fidget.
These are the things we still need to learn.
We don’t really know the full extent of it yet.
Coming up next:
What do we know about the genetics of ADHD?