Working memory deficits in adults with ADHD: is there evidence for subtype differences?

Julie B Schweitzer¹ , Russell B Hanford² and Deborah R Medoff³

¹Division of Child Psychiatry, Department of Psychiatry, 737 W. Lombard St., Suite 442, University of Maryland School of Medicine, Baltimore, Maryland, 21201, USA

²Department of Psychology, 532 Kilgo Circle, Emory University, Atlanta, Georgia, 30322, USA

³Division of Services Research, Department of Psychiatry, 737 W. Lombard St., University of Maryland School of Medicine, Baltimore, Maryland, 21201, USA

author email corresponding author email

Behavioral and Brain Functions 2006, 2:43doi:10.1186/1744-9081-2-43


Published:	15 December 2006

Abstract

Background

Working memory performance is important for maintaining functioning in cognitive, academic and social activities. Previous research suggests there are prevalent working memory deficits in children with attention deficit hyperactivity disorder (ADHD). There is now a growing body of literature characterizing working memory functioning according to ADHD subtypes in children. The expression of working memory deficits in adults with ADHD and how they vary according to subtype, however, remains to be more fully documented.

Methods

This study assessed differences in working memory functioning between Normal Control (NC) adults (N = 18); patients with ADHD, Combined (ADHD-CT) Type ADHD (N = 17); and ADHD, Inattentive (ADHD-IA) Type (N = 16) using subtests from the Wechsler Adult Intelligence Scale-III and Wechsler Memory Scale-III and the Paced Auditory Serial Addition Task (PASAT).

Results

The ADHD groups displayed significant weaknesses in contrast to the NC group on working memory tests requiring rapid processing and active stimulus manipulation. This included the Letter-Number-Sequencing test of the Wechsler scales, PASAT omission errors and the longest sequence of consecutive correct answers on the PASAT. No overall ADHD group subtype differences emerged; however differences between the ADHD groups and the NC group varied depending on the measure and the gender of the participants. Gender differences in performance were evident on some measures of working memory, regardless of group, with males performing better than females.

Conclusion

In general, the data support a dimensional interpretation of working memory deficits experienced by the ADHD-CT and ADHD-IA subtypes, rather than an absolute difference between subtypes. Future studies should test the effects of processing speed and load on subtype performance and how those variables interact with gender in adults with ADHD.