Deficient interference control during working memory updating in adults with ADHD: An event-related potential study.

OBJECTIVE: Little is known about the underlying mechanisms of poor working memory (WM) performance of adults with attention deficit hyperactivity disorder (ADHD). This study investigates interference and load effects during WM updating by use of event-related potentials. METHOD: Forty ADHD patients and 41 controls performed verbal n-back tasks under conditions of low and high WM load. Intrusion probes, i.e., lures, were implemented to challenge interference control abilities during WM processing. RESULTS: Stimulus-dependent N200 amplitude modulation and behavioral performance in lure trials were reduced in adults with ADHD compared to healthy controls. Also, P300 amplitudes tended to be less sensitive to WM load in patients with ADHD. CONCLUSION: Our findings provide electrophysiological evidence for inaccurate discrimination of stimulus categories. Particularly, deficient interference control may lead to overt WM deficits in adult subjects with ADHD. SIGNIFICANCE: The current findings contribute to a deeper understanding of the neural substrates of executive dysfunction in adult ADHD, focusing on the domain of WM.

Electrophysiological indices of error monitoring in juvenile and adult attention deficit hyperactivity disorder (ADHD)--a meta-analytic appraisal.

Attempts to identify the central disturbed processes explaining the overt symptoms of juvenile and adult ADHD rely heavily on the concept of deficient error monitoring processes. A number of studies have investigated event-related potentials (ERPs) and behavioral performance in tasks traditionally used to probe the interference control and inhibition of motor responses. The inspection of the error negativity (Ne/ERN) and error positivity (Pe) components evoked in these tasks has produced conflicting results with respect to the nature and extent of an error monitoring deficit in ADHD. A meta-analytic aggregation of these single studies should help develop a reliable appraisal of the evidence for the compromised performance monitoring processes in ADHD. Our meta-analysis was confined to studies of adult and juvenile ADHD participants examined in GoNogo and Flanker task studies that also reported the Ne/ERN and Pe ERP components. Only seven studies were suited for the meta-analysis, but their aggregation nevertheless led to clear results: Ne was attenuated in adult and adolescent ADHD participants for both tasks, and Pe was attenuated only in the GoNogo tasks. The ADHD participants made more errors than the controls in both tasks but responded slower only in the Flanker task. To our knowledge, this meta-analysis is the first to compare electrophysiological and behavioral indices of error monitoring in adult and juvenile ADHD patients and healthy controls. Admittedly, the data available for this comparison were sparse and heterogeneous; nevertheless, this meta-analysis produced salient results that indicate a monitoring deficit as a central feature of the ADHD syndrome.