12/20/2025
ADHD is a complex disorder associated with detectable differences in the structure of the brain. In general, parts of the brain in children with ADHD tend to be smaller in volume compared to children without ADHD. While this has no impact on a person's intelligence as it's unaffected by ADHD, it does suggest that certain variations in the amygdala, hippocampus, and other structures may account for the symptoms of ADHD.
By adulthood, these variations become less notable. This may also account for why the rate of ADHD in adults is only a fraction of what it is in children.
Brain regions don't operate in isolation. This means that dysfunction in one part of the brain may result in dysfunction in others.
For example, the basal ganglia of children with ADHD tend to have greater interaction of nerve signals (known as functional connectivity) than children without. While increased connectivity may sound like a positive thing, it is associated with a decrease in the diversity of interactions.
So while certain brain processes may move faster, others may fall to the wayside. In children with ADHD, this results in increased hyperactivity and decreased executive functioning.
Decreased blood flow to the prefrontal cortex has also been seen in the ADHD brain. This is referred to as hypofrontality, a condition linked not only to ADHD but also to mental illnesses like bipolar disorder and schizophrenia.
However, unlike those illnesses, the functioning and structure of the ADHD brain can start to become more typical as a person ages. This may explain why childhood ADHD doesn’t always follow you into adulthood or may not be anywhere near as severe.
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