Inhibitory function and working memory in attention defcit/hyperactivity disorder and pervasive developmental disorders: Does a continuous cognitive gradient explain ADHD and PDD traits?

To clarify the relationship between attention deflcit/hyperactivity disorder (AD/HD) and pervasive developmental disorders (PDD), we investigated the common features and differences of these disorders in neuropsychological profiles. The subjects were 4 groups of Japanese boys aged 6 to 15 years, categorized by diagnosis: AD/HD (n = 20), PDD with comorbid AD/HD (PDD+: n = 16), PDD without comorbid AD/HD (PDD-: n = 8), and typically developing (n = 60). We evaluated executive function (EF) through verbal and visuospatial memory tasks, the Go/NoGo task, and the color-word matching Stroop task. We performed a categorical analysis to estimate the effects of the 3 disorders on EF and a dimensional analysis to estimate the effects of symptom scales on EF. We found that the AD/HD and PDD+ subjects had negative effects on verbal working memory and intra-individual response variability. The severity of these impairments was positively correlated with the inattentiveness score. The subjects with a PDD+ or PDD diagnosis had poorer scores on interference control; the severity of this impairment was correlated with the PDD symptom score. Impairments in visuospatial working memory were detected in the AD/HD and PDD groups but not in the PDD+ group. Impairments in inhibition of the prepotent response were noted in all 3 categories. AD/HD and PDD share neuropsychological features, though each disorder has a specific impairment pattern. Our findings partially support the idea that AD/HD and PDD are on a spectrum.