Which of the following is a biological finding in patients with attention deficit-hyperactivity disorder (ADHD)?

Choice A reason: Although structural imaging may show small variations in multiple regions, reduced thalamic volume alone is not consistently observed or diagnostic in ADHD. Choice B reason: EEG findings in ADHD typically show increased, not decreased, slow-wave activity (especially theta waves), reflecting cortical underarousal. Therefore, this option is inaccurate. Choice C reason: Reduced total brain volume is a consistent biological finding in ADHD. Neuroimaging studies show that children and adults with ADHD tend to have smaller total brain volume, particularly in the prefrontal cortex, basal ganglia, and cerebellum. These differences reflect delayed cortical maturation and reduced neural connectivity, which underlie impaired executive functioning, attention control, and impulse regulation. Choice D reason: ADHD is associated with delayed cortical maturation rather than early maturation. The developmental lag particularly affects the prefrontal regions involved in planning, inhibition, and working memory.