Transcranial direct current stimulation in attention-deficit hyperactivity disorder: A meta-analysis of neuropsychological deficits.

Mohammad Ali Salehinejad,Miles Wischnewski,Vahid Nejati,Michael A Nitsche,Carmelo M Vicario,Alessio Avenanti

doi:10.1371/journal.pone.0215095

Abstract

Transcranial direct current stimulation (tDCS) is a promising method for altering cortical excitability with clinical implications in neuropsychiatric diseases. Its application in neurodevelopmental disorders especially attention-deficit hyperactivity disorder (ADHD), is in early stage and promising but its effectiveness has not been systematically examined yet. We conducted a meta-analysis on the effectiveness of tDCS on the most studied neuropsychological symptoms of ADHD, which is the first reported meta-analysis of tDCS studies on ADHD. Data from 10 randomized controlled studies (including 11 separate experiments) targeting inhibitory control, and/or working memory (WM) in ADHD were included. Results show that overall tDCS significantly improved inhibitory control. Sub-analyses further show that dorsolateral prefrontal cortex (dlPFC) (but not right inferior frontal gyrus) tDCS and anodal (but not cathodal) tDCS significantly improved inhibitory control with a small effect size. Anodal dlPFC-tDCS had the largest significant effect on inhibitory control with a small-to-medium effect size. Additionally, a significant improving effect of tDCS on inhibitory control accuracy (but not response time) and WM speed (but not accuracy) were found. Overall, this meta-analysis supports a beneficial effect of tDCS on inhibitory control and WM in ADHD with a small-to-medium effect size. TDCS seems to be a promising method for improving neuropsychological and cognitive deficits in ADHD. However, there might be a dissociation between neuropsychological deficits and clinical symptoms of ADHD and therefore, the significance of this meta-analysis for clinical purposes is limited. Future studies should systematically evaluate the role of inter-individual factors (i.e., ADHD subtype, types of the deficit) and stimulation parameters (i.e., site, polarity, intensity, duration, repetition rate) on tDCS efficacy in ADHD population and examine whether benefits are long-term.

Highlights

Attention-deficit hyperactivity disorder (ADHD) is the most common neurodevelopmental disorder with an estimate of 11% prevalence in school-age children [1]
We describe the effect size obtained from studies to examine the efficacy of Transcranial direct current stimulation (tDCS) in ADHD major neuropsychological symptoms (Please see Fig 2)
Further sub-analyses yielded the following findings: (1) tDCS has an overall significant cumulative effect on inhibitory control in ADHD with a small effect size, (2) when the targeted brain region is taken into account, only tDCS over the dorsolateral prefrontal cortex (PFC) (dlPFC) had a significant effect on inhibitory control, but not tDCS over the right inferior frontal gyrus (rIFG), (3) when stimulation polarity was taken into account, only anodal, but not cathodal tDCS had a significant effect on inhibitory control, (4) when both polarity and targeted region are taken into account, only anodal tDCS of the dlPFC had a significant effect on inhibitory control with a small-tomedium effect size, (5) and when analyzing inhibitory control outcomes separately, tDCS had a significant cumulative effect on accuracy, but not speed

Summary

Introduction

Attention-deficit hyperactivity disorder (ADHD) is the most common neurodevelopmental disorder with an estimate of 11% prevalence in school-age children [1]. Poor inhibitory control resulting from executive dysfunctions (i.e., inhibition-based model) and impulse-control deficits leading to hyperactivity (i.e., motivational dysfunction model) are two influential theories for neural foundations of ADHD [15, 16] These major symptoms have been linked to frontostriatal circuitry and prefrontal cortex (PFC) abnormalities and can be diverged in the “prefrontal hypothesis of ADHD” [17]. An adaptive increase of posterior parietal activity accompanies the respective hypoactivity of frontostriatal regions during performance of executive tasks [19] These findings suggest that ADHD symptoms/causes stem from disturbances in large-scale brain networks [23, 24] and structural, functional and neurochemical abnormalities in cortical and subcortical structures [13, 17, 25], which should be considered in therapeutic interventions

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Discussion

Conclusion