title: The effect of the interval-between-sessions on prefrontal transcranial direct current stimulation (tDCS) on cognitive outcomes: a systematic review and meta-analysis.
abstract: Recently, there has been wide interest in the effects of transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC) on cognitive functioning. However, many methodological questions remain unanswered. One of them is whether the time interval between active and sham-controlled stimulation sessions, i.e. the interval between sessions (IBS), influences DLPFC tDCS effects on cognitive functioning. Therefore, a systematic review and meta-analysis was performed of experimental studies published in PubMed, Science Direct, and other databases from the first data available to February 2016. Single session sham-controlled within-subject studies reporting the effects of tDCS of the DLPFC on cognitive functioning in healthy controls and neuropsychiatric patients were included. Cognitive tasks were categorized in tasks assessing memory, attention, and executive functioning. Evaluation of 188 trials showed that anodal vs. sham tDCS significantly decreased response times and increased accuracy, and specifically for the executive functioning tasks, in a sample of healthy participants and neuropsychiatric patients (although a slightly different pattern of improvement was found in analyses for both samples separately). The effects of cathodal vs. sham tDCS (45 trials), on the other hand, were not significant. IBS ranged from less than 1 h to up to 1 week (i.e. cathodal tDCS) or 2 weeks (i.e. anodal tDCS). This IBS length had no influence on the estimated effect size when performing a meta-regression of IBS on reaction time and accuracy outcomes in all three cognitive categories, both for anodal and cathodal stimulation. Practical recommendations and limitations of the study are further discussed.
authors.affiliation: Department of Psychiatry and Medical Psychology, University Hospital Ghent (UZ Ghent), Ghent University, 1K12F, De Pintelaan 185, 9000, Ghent, Belgium. josefien.dedoncker@gmail.com.|Ghent Experimental Psychiatry (GHEP) Lab, Ghent University, Ghent, Belgium. josefien.dedoncker@gmail.com.
authors.forename: Josefien
authors.initials: J
authors.lastname: Dedoncker
authors.affiliation: Service of Interdisciplinary Neuromodulation, Laboratory of Neurosciences (LIM-27), Department and Institute of Psychiatry, University of São Paulo, São Paulo, Brazil.
authors.forename: Andre R
authors.initials: AR
authors.lastname: Brunoni
authors.affiliation: Department of Psychiatry and Medical Psychology, University Hospital Ghent (UZ Ghent), Ghent University, 1K12F, De Pintelaan 185, 9000, Ghent, Belgium.|Ghent Experimental Psychiatry (GHEP) Lab, Ghent University, Ghent, Belgium.|Faculty of Medicine and Pharmacy, Department of Psychiatry, University Hospital Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), Brussels, Belgium.
authors.forename: Chris
authors.initials: C
authors.lastname: Baeken
authors.affiliation: Department of Psychiatry and Medical Psychology, University Hospital Ghent (UZ Ghent), Ghent University, 1K12F, De Pintelaan 185, 9000, Ghent, Belgium.|Ghent Experimental Psychiatry (GHEP) Lab, Ghent University, Ghent, Belgium.|Faculty of Medicine and Pharmacy, Department of Psychiatry, University Hospital Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), Brussels, Belgium.|Department of Experimental Clinical and Health Psychology, Ghent University, Ghent, Belgium.
authors.forename: Marie-Anne
authors.initials: MA
authors.lastname: Vanderhasselt
mesh_terms: D003071:Cognition / Q000502:physiology*; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D006801:Humans; D009483:Neuropsychological Tests; D017397:Prefrontal Cortex / Q000502:physiology*; D012621:Seasons; D065908:Transcranial Direct Current Stimulation
keywords: Cognition; Dorsolateral prefrontal cortex; Meta-analysis; Noninvasive brain stimulation; Systematic review; Transcranial direct current stimulation