title: Oscillating Square Wave Transcranial Direct Current Stimulation (tDCS) Delivered During Slow Wave Sleep Does Not Improve Declarative Memory More Than Sham: A Randomized Sham Controlled Crossover Study.
abstract: BACKGROUND
  A 2006 trial in healthy medical students found that anodal slow oscillating tDCS delivered bi-frontally during slow wave sleep had an enhancing effect in declarative, but not procedural memory. Although there have been supporting animal studies, and similar findings in pathological groups, this study has not been replicated, or refuted, in the intervening years. We therefore tested these earlier results for replication using similar methods with the exception of current waveform (square in our study, nearly sinusoidal in the original).
  
  
  OBJECTIVE
  Our objective was to test the findings of a 2006 trial suggesting bi-frontal anodal tDCS during slow wave sleep enhances declarative memory.
  
  
  METHODS
  Twelve students (mean age 25, 9 women) free of medical problems underwent two testing conditions (active, sham) in a randomized counterbalanced fashion. Active stimulation consisted of oscillating square wave tDCS delivered during early Non-Rapid Eye Movement (NREM) sleep. The sham condition consisted of setting-up the tDCS device and electrodes, but not turning it on during sleep. tDCS was delivered bi-frontally with anodes placed at F3/F4, and cathodes placed at mastoids. Current density was 0.517 mA/cm(2), and oscillated between zero and maximal current at a frequency of 0.75 Hz. Stimulation occurred during five-five minute blocks with 1-min inter-block intervals (25 min total stimulation). The primary outcomes were both declarative memory consolidation measured by a paired word association test (PWA), and non-declarative memory, measured by a non-dominant finger-tapping test (FTT). We also recorded and analyzed sleep EEG.
  
  
  RESULTS
  There was no difference in the number of paired word associations remembered before compared to after sleep [(active = 3.1 ± 3.0 SD more associations) (sham = 3.8 ± 3.1 SD more associations)]. Finger tapping improved, (non-significantly) following active stimulation [(3.6 ± 2.7 SD correctly typed sequences) compared to sham stimulation (2.3 ± 2.2 SD correctly typed sequences)].
  
  
  CONCLUSIONS
  In this study, we failed to find improvements in declarative or performance memory and could not replicate an earlier study using nearly identical settings. Specifically we failed to find a beneficial effect on either overnight declarative or non-declarative memory consolidation via square-wave oscillating tDCS intervention applied bi-frontally during early NREM sleep. It is unclear if the morphology of the tDCS pulse is critical in any memory related improvements.
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA. Electronic address: sahlem@musc.edu.
authors: Gregory L
authors: GL
authors: Sahlem
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA; Department of Neurosciences, Medical University of South Carolina, 68 President St, BE 101, MSC 501, Charleston, SC 29425, USA.
authors: Bashar W
authors: BW
authors: Badran
authors: Department of Neurology, Medical University of South Carolina, 96 Jonathan Lucas St., CSB 301, Charleston, SC 29425, USA.
authors: Jonathan J
authors: JJ
authors: Halford
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA; Department of Neurology, Medical University of South Carolina, 96 Jonathan Lucas St., CSB 301, Charleston, SC 29425, USA.
authors: Nolan R
authors: NR
authors: Williams
authors: Department of Public Health Sciences, Medical University of South Carolina, 135 Cannon Street Suite 303, MSC 835, Charleston, SC 29425-8350 USA.
authors: Jeffrey E
authors: JE
authors: Korte
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA.
authors: Kimberly
authors: K
authors: Leslie
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA.
authors: Martha
authors: M
authors: Strachan
authors: Department of Neurosciences, Medical University of South Carolina, 68 President St, BE 101, MSC 501, Charleston, SC 29425, USA.
authors: Jesse L
authors: JL
authors: Breedlove
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA.
authors: Jennifer
authors: J
authors: Runion
authors: Department of Neurology, Medical University of South Carolina, 96 Jonathan Lucas St., CSB 301, Charleston, SC 29425, USA.
authors: David L
authors: DL
authors: Bachman
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA.
authors: Thomas W
authors: TW
authors: Uhde
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA.
authors: Jeffery J
authors: JJ
authors: Borckardt
authors: Department of Psychiatry, Medical University of South Carolina, 67 President St., 502N, Charleston, SC 29425, USA; Department of Neurology, Medical University of South Carolina, 96 Jonathan Lucas St., CSB 301, Charleston, SC 29425, USA; Department of Neurosciences, Medical University of South Carolina, 68 President St, BE 101, MSC 501, Charleston, SC 29425, USA; Ralph H. Johnson VA Medical Center, 109 Bee Street, Charleston, SC 29401, USA.
authors: Mark S
authors: MS
authors: George
mesh_terms: D000328:Adult; D001245:Association Learning / Q000502:physiology; D018592:Cross-Over Studies; D004569:Electroencephalography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D016037:Single-Blind Method; D012890:Sleep / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Cognitive enhancement; Memory consolidation; Sleep; Slow wave sleep; Transcranial direct current stimulation