title: A Meta-analysis of Transcranial Direct Current Stimulation Studies Examining the Reliability of Effects on Language Measures.
abstract: BACKGROUND
  Transcranial direct current stimulation (tDCS) is a brain stimulation technique used to examine causal relationships between brain regions and cognitive functions. The effects from tDCS are complex, and the extent to which stimulation reliably affects different cognitive domains is not fully understood and continues to be debated.
  
  
  OBJECTIVE
  To conduct a meta-analysis of studies examining the effects of single-session anodal tDCS on language.
  
  
  METHODS
  The meta-analysis examined the behavioral results from eleven experiments of single-session anodal tDCS and language processing in healthy adults. The means and standard deviations of the outcome measures were extracted from each experiment and entered into the meta-analyses. In the first analysis, we examined the effects of single-session tDCS across all language studies. Next, a series of sub-analyses examined the effects of tDCS on specific tasks and stimulation protocols.
  
  
  RESULTS
  There was a significant effect from anodal single-session tDCS in healthy adults compared to sham (P = 0.001) across all language measures. Next, we found significant effects on specific stimulation protocols (e.g., offline measures, P = 0.002), as well as specific tasks and electrode montages (e.g., verbal fluency measures and left prefrontal cortex, P = 0.035).
  
  
  CONCLUSIONS
  The results indicate that single-session tDCS produces significant and reliable effects on language measures in healthy adults.
authors.affiliation: Center for Cognitive Neuroscience, Department of Neurology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Amy R
authors.initials: AR
authors.lastname: Price
authors.affiliation: Perelman School of Medicine, University of Pennsylvania, Philadelphia PA 19104, USA.
authors.forename: Harrison
authors.initials: H
authors.lastname: McAdams
authors.affiliation: Center for Cognitive Neuroscience, Department of Neurology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Murray
authors.initials: M
authors.lastname: Grossman
authors.affiliation: Center for Cognitive Neuroscience, Department of Neurology, University of Pennsylvania, Philadelphia, PA 19104, USA; Perelman School of Medicine, University of Pennsylvania, Philadelphia PA 19104, USA. Electronic address: roy.hamilton@uphs.upenn.edu.
authors.forename: Roy H
authors.initials: RH
authors.lastname: Hamilton
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D015203:Reproducibility of Results; D065908:Transcranial Direct Current Stimulation / Q000592:standards*
keywords: Language; Meta-analysis; Reliability; Transcranial direct current stimulation; Verbal fluency; tDCS