The Impact of Bilateral Anodal tDCS over Left and Right DLPFC on Executive Functions in Children with ADHD

Abstract

Transcranial direct current stimulation (tDCS) is increasingly used for therapeutic purposes in attention-deficit hyperactivity disorder (ADHD). The dorsolateral prefrontal cortex (DLPFC) is the most targeted region of tDCS studies in ADHD. There is limited knowledge and mixed results about the relevance of left or right DLPFCs in ADHD’s cognitive deficits. No study so far has investigated the impact of the increased excitability of both left and right DLPFC with anodal tDCS on cognitive deficits in ADHD. Here, we explored the impact of online bilateral anodal left and right DLPFC tDCS on executive dysfunction in children with ADHD. Twenty-two children with ADHD (mean age ± SD =8.86 ± 1.80) received bilateral anodal online tDCS over the left and right DLPFC (1.5 mA, 15 min) in two separate sessions in active and sham states. They underwent a battery of four neuropsychological tasks of executive functions during stimulation that measured working memory, cognitive flexibility, response inhibition, and executive control. Bilateral anodal left and right DLPFC tDCS did not improve performance on working memory, cognitive flexibility, and response inhibition. Executive control was, however, partially improved for those who received active tDCS first. The upregulation of bilateral DLPFC tDCS with anodal polarity does not improve executive dysfunction in children with ADHD. The unilateral modulation of DLPFC with anodal tDCS may be more beneficial to cognitive deficits in ADHD in light of previous works targeting only left and/or right DLPFC.

Transcranial random noise stimulation (tRNS) improves hot and cold executive functions in children with attention deficit-hyperactivity disorder (ADHD)

“…Another experiment of this study did not report improvement in cognitive flexibility during anodal right cathodal left dlPFC stimulation and an reversed order electrode placement compared to sham condition 53 . A bilateral anodal dlPFC stimulation study showed no alteration of WCST measures during real, as compared to sham stimulation 36 . Given different stimulation modalities and target areas, we cannot make a clear conclusion about the role of the dlPFC and vmPFC in cognitive flexibility based on these studies.…”

“…In accordance, anodal left/cathodal right dlPFC stimulation improved working memory performance 33 , while anodal stimulation of the right dlPFC with an extracranial reference electrode improved inhibitory control in children with ADHD 35 . However, an online bilateral anodal left and right dlPFC stimulation protocol with extracranial reference electrodes did not improve working memory, inhibitory control and cognitive flexibility, as compared with sham stimulation in children with ADHD 36 . A face to face tES study in ADHD recently compared tDCS (anodal dlPFC/cathodal vmPFC stimulation) with tRNS (bilateral dlPFC stimulation) in ADHD, and found a larger tRNS effect on ADHD symptoms, and working memory performance 37 .…”

“…In sum, based on previous ADHD studies, improved prepotent inhibition has been described during upregulation of the right dlPFC, coupled with an extracranial reference electrode 35 , 56 . This effect vanished when simultaneously stimulation with identical polarity was applied to the left dlPFC 36 , indicating transcallosal inhibition. Moreover, improved prepotent inhibition has been described during upregulation of the right vmPFC either combined with an extracranial return electrode 57 , or left dorsolateral prefrontal cathodal stimulation 52 , 53 .…”

“…For prepotent inhibition, the results of the present study showed improved No-Go accuracy during stimulation compared to sham tRNS. Several tDCS studies in children with ADHD showed that anodal left dlPFC stimulation with the reference electrode over the right vmPFC 48 , 49 , right primary motor area 50 or right dlPFC 35 , 36 , 51 found no effect of stimulation on No-Go accuracy. This makes it improbable that right vmPFC stimulation in the present study caused these results.…”

Efficacy and safety of transcranial direct current stimulation over the left dorsolateral prefrontal cortex in children and adolescents with attention-deficit/hyperactivity disorder: a randomized, triple-blinded, sham-controlled, crossover trial

“…The stimulation time in the active group was 15 min, with a current intensity of 1.5 mA. Bilateral anodal left and right DLPFC tDCS did not enhance performance regarding inhibitory control, working memory, and cognitive flexibility ( 47 ).…”