Attention-deficit/hyperactivity disorder (ADHD) is often talked about as if it were a single condition. But anyone who works with children with ADHD—or raises one—knows that symptoms can look very different from one child to another. A new brain imaging study now provides scientific evidence for this everyday observation, showing that ADHD is not one-size-fits-all at the level of brain structure.
In a recent study published in General Psychiatry, researchers from Shandong First Medical University in China analysed brain scans from children and adolescents with ADHD to better understand how changes in the brain relate to different behavioural symptoms. Using structural MRI data from 135 young people with ADHD and 182 neurotypical controls, the team focused on grey matter volume—an important measure linked to brain development and function.
At first glance, comparing all children with ADHD to those without did not reveal clear differences in brain structure. This surprising result may explain why previous brain imaging studies of ADHD have often produced inconsistent findings. According to the researchers, the reason is simple: ADHD is highly heterogeneous, meaning that different children may show very different brain patterns that cancel each other out when analysed together.
To address this problem, the researchers used a machine-learning approach to divide children with ADHD into subgroups based on their brain structure. This analysis revealed two distinct ADHD subtypes, each with its own pattern of brain changes and behavioural associations.
The first subtype was mainly linked to problems with attention. Children in this group showed increases in grey matter volume, particularly in the frontal cortex and the cerebellum—regions known to play key roles in attention control, planning, and coordination. As attention-related symptoms became more pronounced, these brain changes became more evident. This suggests that, for some children, ADHD may primarily involve altered development in attention-related brain networks.
The second subtype told a different story. These children were more likely to show widespread reductions in grey matter volume as symptoms became more severe. The most affected regions included the cerebellum and the hippocampus, areas involved in motor control, emotional regulation, memory, and motivation. Rather than being linked to a single symptom, this subtype was associated with overall disease severity, including both inattentive and hyperactive or impulsive behaviours.
Importantly, the researchers went a step further by examining how brain changes and symptoms might influence each other over time. Using a novel analysis method, they found that the two subtypes showed different "causal" patterns between brain regions and behaviour. In simple terms, the brain networks involved in attention appeared to play a stronger role in one subtype, while more widespread brain systems were involved in the other.
These findings have important implications. They suggest that children diagnosed with ADHD may have fundamentally different patterns of brain development, even if they share the same clinical label. This could help explain why some children respond well to certain treatments—such as attention-focused cognitive training—while others require more intensive or combined approaches, including medication and behavioural therapy.
While the study does not change clinical practice overnight, it adds to growing evidence that ADHD should be understood as a spectrum of related conditions rather than a single disorder. In the future, brain-based subtyping could support more personalised diagnosis and treatment, helping each child receive care that better matches their underlying neurobiology.
