Working memory in school-aged children with attention-deficit/hyperactivity disorder combined type: Are deficits modality specific and are they independent of impaired inhibitory control?

Research title: Working memory in school-aged children with attention-deficit/hyperactivity disorder combined type: Are deficits modality specific and are they independent of impaired inhibitory control?

Researchers: Karin C. Brocki, Kate D. Randall, Gunilla Bohlin, Kimberly A. Kerns

Published: Journal of Clinical and Experimental Neuropsychology

The focus of this study was two-fold. First, the researchers were interested in comparing boys with ADHD Combined Type to typically developing boys on different aspects of their working memory (WM) performance. Second, they planned to test whether any group differences in WM that were found were independent of deficits in inhibitory control, i.e., the ability to refrain from enacting a primed but irrelevant response, that also characterize children with ADHD. Documenting the latter would contribute to establishing WM deficits as playing a unique role in the difficulties with academic functioning that many children with ADHD experience.

Participants were 31 7- to 12-year old boys with ADHD and 34 matched comparison boys without ADHD. All boys completed a series of computer tasks designed to measure different components of WM, i.e., verbal, visuo-spatial, as well as the central executive (CE) component. The verbal and visuo-spatial storage components are responsible for the short-term storage and rehearsal of visual and visuo-spatial information respectively. The Central Executive component (CE) is thought to be an attentional controller responsible for oversight and coordination of the 2 storage systems. Functions of the CE include focusing attention, dividing attention among concurrent tasks, and providing an interface between working memory and long-term memory. Boys also completed several tasks designed to assess response inhibition. Children had been off medication for at least 24 hours at the time of testing.

Results indicated that in relation to comparison boys, those with ADHD showed poorer performance on multiple aspects of WM; as expected, they also displayed poorer inhibitory control. WM differences were greatest on those tasks that taxed the central executive component of WM, which is consistent with the notion that this component of WM functions as an ‘attentional controller’. Of particular interest was that WM deficits in boys with ADHD remained evident even when their poorer performances on inhibitory control measures were taken into account. This suggests that problems in WM make a unique contribution to learning-related difficulties that many children with ADHD experience, and supports the value of interventions designed to compensate for these WM impairments and/or those that work directly on enhancing their WM capacity.