Inhibitory deficits in attention-deficit/hyperactivity disorder are independent of basic processing efficiency and IQ

Area of Science:

• Neuropsychology
• Developmental Psychology
• Child Psychiatry

Background:

• Attention-deficit/hyperactivity disorder (ADHD) is frequently associated with impaired inhibitory control in children.
• Existing research has not fully clarified the scope of these deficits across different inhibitory domains, their relation to non-executive functions, or their persistence into adolescence.

Purpose of the Study:

• To investigate the extent of inhibitory control deficits in children and adolescents with ADHD.
• To examine the relationship between inhibitory deficits and non-executive functions, including IQ and simple reaction time.
• To determine if inhibitory deficits in ADHD persist into adolescence.

Main Methods:

• Seventy-seven children and adolescents diagnosed with ADHD and 50 typically developing controls completed three inhibitory tasks.
• Participants also underwent a simple two-choice reaction time (2CR) task and an IQ assessment.

Main Results:

• Individuals with ADHD demonstrated moderate deficits across all inhibitory tasks (effect sizes ranging from d=0.5 to 0.9).
• These inhibitory deficits were equally pronounced in both childhood and adolescent age groups.
• Inhibitory impairments were not correlated with IQ scores and remained statistically significant even after controlling for simple reaction time performance.

Conclusions:

• Inhibitory control deficits play a significant, yet constrained, role in ADHD.
• The findings support current perspectives on the neuropsychological heterogeneity of ADHD.
• Deficits in inhibitory control are a persistent feature of ADHD from childhood through adolescence, independent of intellectual capacity.