title: Bifrontal transcranial direct current stimulation slows reaction time in a working memory task.
abstract: BACKGROUND
  Weak transcortical direct current stimulation (tDCS) applied to the cortex can shift the membrane potential of superficial neurons thereby modulating cortical excitability and activity. Here we test the possibility of modifying ongoing activity associated with working memory by tDCS. The concept of working memory applies to a system that is capable of transiently storing and manipulating information, as an integral part of the human memory system. We applied anodal and cathodal transcranial direct current (tDCS) stimulation (260 microA) bilaterally at fronto-cortical electrode sites on the scalp over 15 min repeatedly (15 sec-on/15 sec-off) as well as sham-tDCS while subjects performed a modified Sternberg task.
  
  
  RESULTS
  Reaction time linearly increased with increasing set size. The slope of this increase was closely comparable for real and sham stimulation indicating that our real stimulation did not effect time required for memory scanning. However, reaction time was slowed during both anodal and cathodal stimulation as compared to placebo (p < 0.05) indicating that real stimulation hampered neuronal processing related to response selection and preparation.
  
  
  CONCLUSIONS
  Intermittent tDCS over lateral prefrontal cortex during a working memory task impairs central nervous processing related to response selection and preparation. We conclude that this decrease in performance by our protocol of intermittent stimulation results from an interference mainly with the temporal dynamics of cortical processing as indexed by event-related sustained and oscillatory EEG activity such as theta.
authors.affiliation: University of Lübeck, Department of Neuroendocrinology H23a, Ratzeburger Allee 160, 23538 Lübeck, Germany. marshall@kfg.uni-luebeck.de
authors.forename: Lisa
authors.initials: L
authors.lastname: Marshall
authors.forename: Matthias
authors.initials: M
authors.lastname: Mölle
authors.forename: Hartwig R
authors.initials: HR
authors.lastname: Siebner
authors.forename: Jan
authors.initials: J
authors.lastname: Born
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008568:Memory / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*