Viability of a compensatory working memory model of attention deficit hyperactivity disorder

Abstract

A working memory dysfunction has been posited as a possible endophenotype for Attention Deficit Hyperactivity Disorder (ADHD). Indeed, recent data tend to corroborate this construct as perhaps a core factor in accounting for the tripartite symptomatology of ADHD (hyperactivity, inattentiveness and impulsivity). Working memory is one of the executive functions subserved by the prefrontal cortex. A challenging, yet to be solved, issue for the Working Memory Model of ADHD is that the typical onset of ADHD symptoms occurs prior to the central involvement of the anterior part of the brain in mediating behaviour. There are known prefrontal-subcortical brain circuits. The globus pallidus, a structure of the basal ganglia, is discussed with reference to having a working memory role in a subcortical-prefrontal network. We review neuroscience models of working memory together with multidisciplinary data leading to the hypothesis that subcortical malfunction in early childhood can result in storage of irrelevancies, taxing working memory capacity. This, in theory, could account for early ADHD onset. In turn, the later developmental capacity of the prefrontal cortex to compensate for subcortical working memory difficulties will determine whether or not ADHD symptoms will continue or naturally attenuate. The feasibility and importance of devising studies capable of refuting the early-onset working memory developmental hypothesis is discussed.

Keywords:

• working memory
• ADHD
• globus pallidus
• endophenotype