Dissociation of working memory impairments and attention-deficit/hyperactivity disorder in the brain

Abstract

Prevailing neuropsychological models of attention-deficit/hyperactivity disorder (ADHD) propose that ADHD arises from deficits in executive functions such as working memory, but accumulating clinical evidence suggests a dissociation between ADHD and executive dysfunctions. This study examined whether ADHD and working memory capacity are behaviorally and neurobiologically separable using functional magnetic resonance imaging (fMRI). Participants diagnosed with ADHD in childhood who subsequently remitted or persisted in their diagnosis as adults were characterized at follow-up in adulthood as either impaired or unimpaired in spatial working memory relative to controls who never had ADHD. ADHD participants with impaired spatial working memory performed worse than controls and ADHD participants with unimpaired working memory during an n-back working memory task while being scanned. Both controls and ADHD participants with unimpaired working memory exhibited significant linearly increasing activation in the inferior frontal junction, precuneus, lingual gyrus, and cerebellum as a function of working-memory load, and these activations did not differ significantly between these groups. ADHD participants with impaired working memory exhibited significant hypoactivation in the same regions, which was significantly different than both control participants and ADHD participants with unimpaired working memory. These findings support both a behavioral and neurobiological dissociation between ADHD and working memory capacity.

Complexity analysis of fNIRS signals in ADHD children during working memory task

“…This indicates that greater working memory demands evoke greater activations in brain regions associated with working memory, including dorsolateral prefrontal cortex, inferior frontal junction 39 . Additionally, in the ADHD group, there are functional deficits of right DLPFC which is as the main neural correlate of the central executive 43 .…”

Structure–function relationships in the developing cerebellum: Evidence from early-life cerebellar injury and neurodevelopmental disorders

“…Among the neurodevelopmental disorders with established links to cerebellar dysfunction, executive function deficits are most characteristic of ADHD. A recent study indicated that ADHD participants with impaired working memory show hypoactivation in the anterior cerebellum [56] and that bilateral regions of Crus I were hypoactive in ADHD participants during a working memory paradigm [57]. Gray matter reductions have been reported in multiple cerebellar regions in ADHD [35], including those that are associated with dorsal and ventral attention networks, and reduced functional connectivity has been found in cerebellar regions involved in fronto-parietal networks in children with ADHD [58].…”

A dimensional approach to modeling symptoms of neuropsychiatric disorders in the marmoset monkey

“…Whilst evidence from the clinical literature supports global prefrontal impairment in ADHD (Lenartowicz et al, 2014;Arai et al, 2015;Mattfeld et al, 2015) and schizophrenia patients (Manoach, 2003;Orfei et al, 2013;Pu et al, 2013;Marumo et al, 2014;Buchy et al, 2015), the identification of the vlPFC as critical for self-ordered spatial memory in marmosets specifically implicates vlPFC impairment in this working memory deficit in patients. This is supported by the accompanying profound dysfunction in attentional set shifting, which also is associated with vlPFC dysfunction.…”