ADHD and Working Memory: The impact of Central Executive Deficits and Exceeding Storage/Rehearsal Capacity on Observed Inattentive Behavior

Research title: ADHD and working memory: The impact of central executive deficits and exceeding storage/rehearsal capacity on observed inattentive behavior.

Researchers: Michael J. Kofler, Mark D. Rapport, Jennifer Bolden, Dustin E. Sarver, Joseph S. Raiker

Published: Journal of Abnormal Child Psychology

The goal of this study was to test whether inattentive behavior in children with ADHD is directly explained by deficits in their working memory (WM) capacity. The researchers predicted that children with ADHD would not show more inattentive behavior than peers during tasks with low WM demands but only when engaged in tasks that taxed their WM.

Participants were 28 boys aged 8 to 12 years; 15 were diagnosed with ADHD, combined type and 14 did not have any psychiatric disorder. All boys engaged in a series of computer tasks that varied in the degree to which successful completion depended on WM. In the low WM condition, boys played with a program which allowed them to draw/paint anything they wanted using a variety of interactive tools. In the WM conditions, they were required to correctly recall either a sequence of numbers/letters in reverse order (verbal WM) or the locations of a series of dots that were flashed on the screen (visuo-spatial WM). Different numbers of number/letters and dots were used on different trials so that children’s maximum WM capacity in each domain could be measured, i.e., the larger the sequence they could recall the greater their capacity. Boys were videotaped during the computer tasks so that the percent of time that were fully engaged and attentive, i.e., oriented to the computer monitor, could be measured.

Results of this study were clear and compelling. During the drawing program, both groups of boys were attentive more than 95% of the time. However, during both WM tasks, the attentive behavior of boys with ADHD dropped off significantly while comparison boys were relatively unaffected. Specifically, rates of attentive behavior for boys in the ADHD group declined from over 95% of the time to roughly 75% of the time. Comparison boys remained inattentive over 95% of the time. The decline in attentive behavior for boys with ADHD emerged even when the tasks did not exceed their WM capacity and got progressively worse as their WM capacity was exceeded. As expected, the WM capacity of comparison boys was significantly greater than that of boys with ADHD – and when differences in WM capacity between the 2 groups was controlled for, group differences in inattentive behavior disappeared.

These results demonstrate that boys with ADHD are not necessarily more inattentive than other boys in all conditions, but only when required to complete tasks that depend heavily on WM. Unfortunately this is the case for much of the academic work required in school. The important implication of these findings is that the inattentive behavior that children with ADHD frequently display at school is a byproduct of their poor WM capacity. The authors conclude with a call to develop interventions that promote the early development of WM abilities.