Children diagnosed with attention deficit hyperactivity disorder (ADHD) who show a notable difference between their verbal and nonverbal cognitive abilities tend to struggle more with self-control and maintaining focus. These pronounced cognitive disparities are associated with diminished blood flow in the brain's frontal lobe during activities that demand impulse regulation. These findings were published in the journal NeuroImage.
ADHD is a prevalent neurodevelopmental condition in school-aged children, characterized by difficulties with sustained attention, excessive physical activity, or impulsive behaviors. These symptoms often arise from impairments in executive functions, which are critical for organizing thoughts, managing emotions, and guiding goal-directed actions.
Psychological assessments typically categorize intelligence into two primary domains: verbal and performance. Verbal intelligence encompasses language-based reasoning, vocabulary, and accumulated general knowledge, while performance intelligence relates to visual processing, spatial reasoning, and practical skills. In typically developing children, these two intelligence measures are usually balanced. However, some children exhibit a wide divergence between these scores, known as an intelligence quotient discrepancy, which previous research suggests is more common in children with attention difficulties.
The research, led by Xin Chen from Fujian Children’s Hospital in China, involved 114 children with ADHD, aged six to twelve, all with a general intelligence score of 70 or higher and not currently on ADHD medication. The participants were divided into two groups: one with a significant verbal-performance score gap and another with balanced intelligence profiles. Parents completed surveys on their children's daily executive function challenges, and the children underwent computerized tests to assess their reaction times and ability to inhibit responses. Brain imaging using functional near-infrared spectroscopy was performed on a subset of 46 children during a task designed to challenge impulse control, measuring changes in oxygenated blood flow in the brain.
The study revealed that children with an intelligence gap scored lower on executive function according to parent reports, particularly struggling with task initiation and transitioning between activities. They also exhibited slower reaction times and more errors in visual inhibition tasks. A significant factor contributing to this gap was identified as arithmetic scores, which require working memory and mental manipulation of numbers. Brain imaging showed reduced blood flow in the right medial prefrontal cortex in children with an intelligence gap during the impulse control task, an area crucial for emotion regulation, motivation, and decision-making. The severity of attention deficits correlated directly with decreased oxygenated blood flow in this frontal region. The study also highlighted 'monitoring'—the ability to supervise one's work—as a key predictor of hyperactivity and scattered attention.
While providing valuable insights, the study acknowledged several limitations, including the use of older assessment editions, a participant pool limited to Chinese children, and the grouping of all ADHD subtypes together. Future research should include larger and more diverse samples, different cognitive tasks, and control groups of typically developing children. Advanced brain imaging techniques could also help filter out superficial interference to better capture deeper brain signals. This research contributes significantly to understanding the neurocognitive mechanisms underlying ADHD, particularly in relation to intelligence discrepancies, paving the way for more targeted interventions and support systems for affected children.