Neural basis of working memory in ADHD: Load versus complexity

Prerona Mukherjee,Tadeus Hartanto,Ana-Maria Iosif,J Faye Dixon,Stephen P Hinshaw,Murat Pakyurek,Wouter Van Den Bos,Amanda E Guyer,Samuel M Mcclure,Julie B Schweitzer,Catherine Fassbender

doi:10.1016/j.nicl.2021.102662

Abstract

Working memory (WM) deficits are key in attention deficit hyperactivity disorder (ADHD). Nevertheless, WM is not universally impaired in ADHD. Additionally, the neural basis for WM deficits in ADHD has not been conclusively established, with regions including the prefrontal cortex, cerebellum, and caudate being implicated. These contradictions may be related to conceptualizations of WM capacity, such as load (amount of information) versus operational-complexity (maintenance-recall or manipulation). For instance, relative to neurotypical (NT) individuals, complex WM operations could be impaired in ADHD, while simpler operations are spared. Alternatively, all operations may be impaired at higher loads. Here, we compared the impact of these two components of WM capacity: load and operational-complexity, between ADHD and NT, behaviorally and neurally. We hypothesized that the impact of WM load would be greater in ADHD, and the neural activation would be altered. Participants (age-range 12–23 years; 50 ADHD (18 females); 82 NT (41 females)) recalled three or four objects (load) in forward or backward order (operational-complexity) during functional magnetic resonance imaging scanning. The effects of diagnosis and task were compared on performance and neural engagement. Behaviorally, we found significant interactions between diagnosis and load, and between diagnosis, load, and complexity. Neurally, we found an interaction between diagnosis and load in the right striatum, and between diagnosis and complexity in the right cerebellum and left occipital gyrus. The ADHD group displayed hypo-activation compared to NT group during higher load and greater complexity. This informs mechanisms of functional problems related to WM in adolescents and young adults with ADHD (e.g., academic performance) and remedial interventions (e.g., WM-training).

Highlights

Attention Deficit Hyperactivity Disorder (ADHD) is a common, earlyonset neurodevelopmental disorder, with an estimated prevalence of 5–6%, often persisting into adulthood (Asherson et al, 2016)
Working memory (WM) deficits have been widely reported in attention deficit hyperactivity disorder (ADHD)
Despite the prominence of WM-related impairments in ADHD, it is unclear whether these WM deficits are driven by increases in WM load or operational-complexity, or both

Summary

Introduction

Attention Deficit Hyperactivity Disorder (ADHD) is a common, earlyonset neurodevelopmental disorder, with an estimated prevalence of 5–6%, often persisting into adulthood (Asherson et al, 2016). A prom inent deficit in ADHD is working memory (WM), with some research suggesting that WM may be a core impairment in ADHD (Martinussen et al, 2005; Rapport et al, 2001). WM impairments are linked to key symptoms such as inattention and hyperactivity in ADHD (Orban et al., 2018; Rapport et al, 2009; Campez et al, 2020). WM-related im pairments can have a profound influence on a variety of functions, affecting areas of life, such as academic achievement (Simone et al, 2018; Fried et al, 2019), emotion processing (Groves et al, 2020), social relationships (Kofler et al, 2011). A more comprehensive understanding of WM-related impairment in ADHD could have impor tant implications

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