Prefrontal oxygenation during working memory in ADHD

Objectives

Deficits in working memory have been repeatedly found on a behavioural level in children with attention-deficit/hyperactivity disorder (ADHD). Functional brain imaging studies have revealed evidence for alterations in the prefrontal cortex associated with working memory. So far it remains unresolved whether object (OWM) and spatial visual working memory (SWM) are distinctly impaired in ADHD. We investigated this issue with the fist multi-channel functional near-infrared spectroscopy study of children with ADHD.

Method

We investigated 19 children with ADHD combined type (DSM-IV) and 19 controls matched for age (8-15 years), sex, handedness, and intelligence during a working memory task assessing OWM and SWM separately, and a control condition (CON). Prefrontal brain activity was measured by concentration changes of oxygenated haemoglobin.

Results

Working memory performance showed significant differences for conditions (OWM > SWM > CON), but no differences between groups. Cortical prefrontal activation was significantly higher for OWM and SWM in contrast to CON, again with no differences between groups.

Conclusions

We found no indication for an altered prefrontal processing during OWM and SWM tasks in ADHD children compared to controls. Reviewing the existing imaging literature on working memory in ADHD and considering the present data, we discuss possible confounding factors relevant for brain activity in previous, the current, and future investigations. Thus, it is of high importance to capture developmental trajectories, task specific discrepancies, and effects of permanent medication intake in future studies.