ADHD is a neurodevelopmental difference, and there is evidence from neuroimaging research that tells us how the brains of those with ADHD are structurally and dynamically different from those without ADHD.
There are structural, functional, and chemical differences in the brains of those with ADHD.
Research shows that brain development in children with ADHD is delayed compared to typically developing children. This delay affects the speed and timing of brain maturation, with differences of around 3 to 5 years depending on the specific area of the brain.
Certain important brain structures are, on average, smaller in children with ADHD. For example, the frontal cortex — the area responsible for self-control and executive functioning — usually reaches its maximum thickness around the age of 6 in children without ADHD. In children with ADHD, this development is delayed, with maximum thickness often not reached until age 9 or later.
The main areas of the brain affected by this delay include the frontal lobe, the temporal lobe as well as subcortical regions, such as the limbic system.
Neuroimaging research shows that in addition to structural differences, there are also functional differences in the brains of individuals with ADHD. These differences are linked to a delay in the development of brain functions, particularly those involved in executive functioning.
When executive functioning is weaker, individuals with ADHD may experience difficulties such as:
In addition to structural and functional differences, research shows that the brains of individuals with ADHD often have lower levels of two important brain chemicals: dopamine and noradrenaline (also known as norepinephrine).
These chemical differences help explain why individuals with ADHD may find it more difficult to sustain attention, regulate behaviour, and stay motivated over time.