ADHD Subtype Differences in Reinforcement Sensitivity and Visuospatial Working Memory.

Both cognitive and motivational deficits are thought to give rise to the problems in the combined (ADHD-C) and inattentive subtype (ADHD-I) of attention-deficit hyperactivity disorder (ADHD). In both subtypes one of the most prominent cognitive weaknesses appears to be in visuospatial working memory (WM), which is composed of short-term memory (STM) and a central executive (CE). In children with ADHD-C, both STM and the CE seem impaired, and together with motivational impairments, give rise to their deficits in visuospatial WM. In children with ADHD-I, no studies investigated these WM components and their interplay with motivational impairments. Effects of a standard (feedback only) and a high level of reinforcement (feedback + 10 euros) on visuospatial WM-, STM-, and CE performance were examined in 27 children with ADHD-I (restrictive-subtype), 70 children with ADHD-C, and 40 typically developing controls (aged 9-12). In both ADHD-subtypes CE and WM performance was worse than in controls. STM performance of children with ADHD-I was, in contrast to that of children with ADHD-C, not different from controls. STM and WM performance was worse in ADHD-C than in ADHD-I, whereas CE-related performance did not differ. High reinforcement improved STM and WM performance in both subtypes but not in controls. This improvement was equally pronounced in both subtypes. High reinforcement did not improve CE-related performance. Both subtypes have equally pronounced motivational deficits, which have detrimental effects on their visuospatial STM and WM performance. In contrast to children with ADHD-C, children with ADHD-I seem unimpaired on visuospatial STM; only an impaired CE and motivational impairments give rise to their deficits in visuospatial WM.