What do brain imaging studies show about Attention Deficit Hyperactivity Disorder (ADHD)?

From the Guidelines

Brain imaging studies have shown that individuals with ADHD have abnormal findings in structural and functional brain imaging, predominantly in larger-scale brain networks such as frontostriatal, frontoparietal, and ventral attention networks. These studies, as discussed in the 2022 review 1, highlight the complex neurobiological underpinnings of ADHD, which is characterized by executive deficits in several cognitive domains, including visuospatial and verbal working memory, inhibitory control, vigilance, planning, and reward regulation. The brain imaging findings are substantiated by the fact that patients with ADHD show a high variability of symptoms on the interindividual and intraindividual level, which need to be viewed within the context of a chronic neurodevelopmental disorder.

Some key points about brain imaging studies in ADHD include:

• Abnormalities in brain structure and function, particularly in regions responsible for attention and executive function 1
• Altered activation patterns during tasks requiring attention and inhibitory control, with reduced activity in frontal regions and abnormal connectivity between neural networks 1
• Dysregulation in dopamine and norepinephrine systems, which explains the effectiveness of certain medications in treating ADHD 1
• Heterogeneity of brain differences across individuals with ADHD, supporting the understanding that ADHD is a complex and variable condition 1

Overall, the evidence from brain imaging studies suggests that ADHD is associated with distinct neurobiological differences, which can inform the development of effective treatments and improve our understanding of this complex condition. The use of brain imaging studies has significantly advanced our knowledge of ADHD, but it is essential to note that imaging cannot yet be used for individual diagnosis, which still relies on clinical assessment of symptoms and behavior.

From the Research

Brain Imaging Studies on ADHD

Brain imaging studies have shown various abnormalities in the brains of individuals with Attention-Deficit/Hyperactivity Disorder (ADHD). Some of the key findings include:

• Abnormalities in the frontal lobes, basal ganglia, and corpus callosum 2
• Decreased surface area in the left ventral frontal and right prefrontal cortex, thinner medial temporal lobes, and smaller caudate nuclei 2
• Alterations in the prefrontal and temporal regions, reflecting perception-action mapping alterations 2
• Changes in cortical thickness and the shape of the inferior frontal cortex, bilateral sensorimotor cortex, left temporal lobe, and insula 2

Subcortical Brain Volume Differences

Studies have also shown subcortical brain volume differences in individuals with ADHD, including:

• Smaller volumes of the accumbens, amygdala, caudate, hippocampus, putamen, and intracranial volume compared to controls 3
• No difference in volume size in the pallidum and thalamus between people with ADHD and controls 3
• A delay of maturation and a delay of degeneration, as effect sizes were highest in most subgroups of children (<15 years) versus adults (>21 years) 3

Structural and Functional Neuroimaging

Structural and functional neuroimaging studies have evidenced differences in volume, surface-based measures, and white matter integrity in different cerebral regions, in children and adults with ADHD compared to population norms 4

• Abnormalities in the basal ganglia, prefrontal structures, and the corpus callosum have been the most consistently reported findings across studies 4
• Hemodynamic and magnetoencephalography measurements have also shown differences in neural activity during the execution of neuropsychological tasks and during rest, in widespread regions of the brain 4

Brain Abnormalities and Medication Effects

Brain abnormalities in ADHD are characterized by multiple functional and structural neural network abnormalities, including fronto-striatal, fronto-parieto-temporal, fronto-cerebellar, and fronto-limbic networks 5

• Evidence from longitudinal structural imaging studies has shown that ADHD is characterized by a delay in structural brain maturation 5
• Dysfunction of the ventrolateral prefrontal cortex seems to be more pronounced in ADHD relative to other pediatric disorders 5
• Methylphenidate may act to normalize activity within the attentional network, specifically in striatal circuitry 6