Prevailing neuropsychological models of attention-deficit/hyperactivity disorder (ADHD) propose that ADHD arises from deficits in executive functions such as working memory, but accumulating clinical evidence suggests a dissociation between ADHD and executive dysfunctions.This study examined whether ADHD and working memory capacity are behaviorally and neurobiologically separable using functional magnetic resonance imaging (f MRI).On each updating step, a variable subset of letters in varying positions in the row had to be updated.The SGS model assumes that on each updating step, participants scan through the memory set sequentially, opening the gate when a letter requires updating, and closing the gate when the next letter needs to be maintained.As is predicted by the SGS model, the reaction times for each updating step increased with the number of updated items and with the number of gate switches.In addition, the present experiment provides direct evidence supporting the scanning assumption of the model.These findings support both a behavioral and neurobiological dissociation between ADHD and working memory capacity.
Participants were required to keep track of the last letter that appeared in each of a row of frames on the screen.
Models of WM suggest that these demands are coordinated by a gate between perceptual input and WM.
Previous work with a letter-updating paradigm (Kessler & Oberauer, , 738–754, 2014) supported a scanning and gate-switching (SGS) model of WM updating.
Participants diagnosed with ADHD in childhood who subsequently remitted or persisted in their diagnosis as adults were characterized at follow-up in adulthood as either impaired or unimpaired in spatial working memory relative to controls who never had ADHD.
ADHD participants with impaired spatial working memory performed worse than controls and ADHD participants with unimpaired working memory during an n-back working memory task while being scanned.