title: Quantitative Review Finds No Evidence of Cognitive Effects in Healthy Populations From Single-session Transcranial Direct Current Stimulation (tDCS).
abstract: BACKGROUND
  Over the last 15-years, transcranial direct current stimulation (tDCS), a relatively novel form of neuromodulation, has seen a surge of popularity in both clinical and academic settings. Despite numerous claims suggesting that a single session of tDCS can modulate cognition in healthy adult populations (especially working memory and language production), the paradigms utilized and results reported in the literature are extremely variable. To address this, we conduct the largest quantitative review of the cognitive data to date.
  
  
  METHODS
  Single-session tDCS data in healthy adults (18-50) from every cognitive outcome measure reported by at least two different research groups in the literature was collected. Outcome measures were divided into 4 broad categories: executive function, language, memory, and miscellaneous. To account for the paradigmatic variability in the literature, we undertook a three-tier analysis system; each with less-stringent inclusion criteria than the prior. Standard mean difference values with 95% CIs were generated for included studies and pooled for each analysis.
  
  
  RESULTS
  Of the 59 analyses conducted, tDCS was found to not have a significant effect on any - regardless of inclusion laxity. This includes no effect on any working memory outcome or language production task.
  
  
  CONCLUSIONS
  Our quantitative review does not support the idea that tDCS generates a reliable effect on cognition in healthy adults. Reasons for and limitations of this finding are discussed. This work raises important questions regarding the efficacy of tDCS, state-dependency effects, and future directions for this tool in cognitive research.
authors.affiliation: University of Melbourne, Melbourne School of Psychological Sciences, Redmond Barry Building, Melbourne, VIC 3010, Australia. Electronic address: jared.cooney.horvath@gmail.com.
authors.forename: Jared Cooney
authors.initials: JC
authors.lastname: Horvath
authors.affiliation: University of Melbourne, Melbourne School of Psychological Sciences, Redmond Barry Building, Melbourne, VIC 3010, Australia.
authors.forename: Jason D
authors.initials: JD
authors.lastname: Forte
authors.affiliation: University of Melbourne, Melbourne School of Psychological Sciences, Redmond Barry Building, Melbourne, VIC 3010, Australia.
authors.forename: Olivia
authors.initials: O
authors.lastname: Carter
mesh_terms: D000328:Adult; D003071:Cognition / Q000502:physiology*; D056344:Executive Function / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009483:Neuropsychological Tests; D065908:Transcranial Direct Current Stimulation
keywords: Executive function; Language; Memory; Quantitative review; Transcranial direct current stimulation (tDCS); Working memory