title: The polarity-dependent effects of the bilateral brain stimulation on working memory.
abstract: BACKGROUND
  Working memory plays a critical role in cognitive processes which are central to our daily life. Neuroimaging studies have shown that one of the most important areas corresponding to the working memory is the dorsolateral prefrontal cortex (DLFPC). This study was aimed to assess whether bilateral modulation of the DLPFC using a noninvasive brain stimulation, namely transcranial direct current stimulation (tDCS), modifies the working memory function in healthy adults.
  
  
  METHODS
  In a randomized sham-controlled cross-over study, 60 subjects (30 Males) received sham and active tDCS in two subgroups (anode left/cathode right and anode right/cathode left) of the DLPFC. Subjects were presented working memory n-back task while the reaction time and accuracy were recorded.
  
  
  RESULTS
  A repeated measures, mixed design ANOVA indicated a significant difference between the type of stimulation (sham vs. active) in anodal stimulation of the left DLPFC with cathodal stimulation of the right DLPFC [F(1,55)= 5.29, P=0.019], but not the inverse polarity worsened accuracy in the 2-back working memory task. There were also no statistically significant changes in speed of working memory [F(1,55)= 0.458,P=0.502] related to type or order of stimulation.
  
  
  CONCLUSIONS
  The results would imply to a polarity dependence of bilateral tDCS of working memory. Left anodal/ right cathodal stimulation of DLPFC could impair working memory, while the reverser stimulation had no effect. Meaning that bilateral stimulation of DLFC would not be a useful procedure to improve working memory. Further studies are required to understand subtle effects of different tDCS stimulation/inhibition electrode positioning on the working memory.
authors.affiliation: Department of Psychology, Shahid Beheshti University, G.C., Tehran, Iran.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Keshvari
authors.affiliation: Department of Psychology, Shahid Beheshti University, G.C., Tehran, Iran ; Instititute for Cognitive & Brain Sciences.
authors.forename: Hamid-Reza
authors.initials: HR
authors.lastname: Pouretemad
authors.affiliation: Institute for Cognitive Sciences Studies (ICSS), Tehran, Iran.
authors.forename: Hamed
authors.initials: H
authors.lastname: Ekhtiari
keywords: Dorsolateral Prefrontal Cortex; Transcranial Direct Current Stimulation; Working Memory