Transcranial Direct Current Stimulation in ADHD: A Systematic Review of Efficacy, Safety, and Protocol-induced Electrical Field Modeling Results

Abstract

Transcranial direct current stimulation (tDCS) is a promising method for altering cortical excitability with clinical implications. It has been increasingly used in neurodevelopmental disorders, especially attention-deficit hyperactivity disorder (ADHD), but its efficacy (based on effect size calculations), safety, and stimulation parameters have not been systematically examined. In this systematic review, we aimed to (1) explore the effectiveness of tDCS on the clinical symptoms and neuropsychological deficits of ADHD patients, (2) evaluate the safety of tDCS application, especially in children with ADHD, (3) model the electrical field intensity in the target regions based on the commonly-applied and effective versus less-effective protocols, and (4) discuss and propose advanced tDCS parameters. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses approach, a literature search identified 14 empirical experiments investigating tDCS effects in ADHD. Partial improving effects of tDCS on cognitive deficits (response inhibition, working memory, attention, and cognitive flexibility) or clinical symptoms (e.g., impulsivity and inattention) are reported in 10 studies. No serious adverse effects are reported in 747 sessions of tDCS. The left and right dorsolateral prefrontal cortex are the regions most often targeted, and anodal tDCS the protocol most often applied. An intensity of 2 mA induced stronger electrical fields than 1 mA in adults with ADHD and was associated with significant behavioral changes. In ADHD children, however, the electrical field induced by 1 mA, which is likely larger than the electrical Electronic supplementary material The online version of this article (

ADHD subtype-specific cognitive correlates and association with self-esteem: a quantitative difference

“…ADHD-I showed improved performance on the execution of an action in an experimental Go/NoGo task while the ADHD-C showed improved ability to withhold a prepotent response tendency in NoGo trials. Recent reviews of non-invasive brain stimulation studies in ADHD also suggests that the efficacy of the treatment could be different in ADHD subtypes [5,6]. Identifying subtype-specific profiles in ADHD, especially cognitive profile, is thus a timely and important topic in the field and is in line with recent findings from neuroimaging studies indicating subtype-specific pattern of activity in different brain regions [13,14].…”

“…More importantly, this is in line with a recently introduced model of ADHD psychopathology, which proposes WM deficits as a major risk factor in ADHD [51] and implies that WM is probably one of the core cognitive deficits in the pathophysiology of all ADHD subtypes, and could be a reasonable target for ADHD treatment. Novel treatment approaches, such as non-invasive brain stimulation that have been promisingly used in ADHD [5,6] also target WM as one of the core deficits in ADHD. In addition to the cognitive correlates, we found a subtype-specific pattern in self-esteem ratings with ADHD-H reporting a higher level of global and total self-esteem compared to other subtypes.…”

“…A precise description of the pathophysiology underlying ADHD is difficult due to its neuropsychological heterogeneity [1] and substantial overlap between ADHD and typically developing children [2]. Cognitive deficits, especially executive dysfunctions, are central to ADHD psychopathology [3] and among the primary treatment targets by pharmacological [4] and novel treatment approaches [5,6]. These cognitive deficits are also heterogeneous in ADHD and thus individual differences in cognitive profile should be considered as well [7].…”

Efficacy and clinical predictors of response to rTMS treatment in pharmacoresistant obsessive-compulsive disorder (OCD): a retrospective study

“…On the other hand, the left DLPFC is involved in cognitive control [64] and increasing its activation with NIBS has been associated with improved control over intrusive thoughts in OCD [36] and cognitive control in other disorders marked with executive dysfunctions [15,17,19,65]. Increasing the left DLPFC with excitatory and right DLPFC with inhibitory stimulation is in line with the putative regions that are affected in OCD and involved in cognitive control and response inhibition/affect respectively [10].…”

Transcranial direct current stimulation (tDCS) combined with cognitive training in adolescent boys with ADHD: a double-blind, randomised, sham-controlled trial

“…Alternatively, given the stronger electric field strengths in children than in adults [96,97], multiple sessions of tDCS may have triggered a homeostatic plasticity responsei.e., the amount and direction of plasticity was attenuated in response to excessive increases in neuronal excitability [98][99][100] -thereby temporarily disrupting the excitability of rIFC [99][100][101]. This is in line with our post-hoc moderation analysis that revealed older but not younger participants improved less in the ADHD-RS Total Scores in the anodal versus sham tDCS group at posttreatment.…”