title: Cross-hemispheric Alternating Current Stimulation During a Nap Disrupts Slow Wave Activity and Associated Memory Consolidation.
abstract: BACKGROUND
  Slow Wave Activity (SWA), the low frequency (<4 Hz) oscillations that characterize Slow Wave Sleep (SWS) are thought to relate causally to declarative memory consolidation during nocturnal sleep. Evidence is conflicting relating SWA to memory consolidation during nap however.
  
  
  OBJECTIVE
  We applied transcranial alternating current stimulation (tACS) - which, with a cross-hemispheric electrode montage (F3 and F4 - International 10:20 EEG system), is able to disrupt brain oscillations-to determine if disruption of low frequency oscillation generation during afternoon nap is causally related to disruption in declarative memory consolidation.
  
  
  METHODS
  Eight human subjects each participated in stimulation and sham nap sessions. A verbal paired associate learning (PAL) task measured memory changes. During each nap period, five 5-min stimulation (0.75 Hz cross-hemispheric frontal tACS) or sham intervals were applied with 1-min post-stimulation intervals (PSI's). Spectral EEG power for Slow (0.7-0.8 Hz), Delta (1.0-4.0 Hz), Theta (4.0-8.0 Hz), Alpha (8.0-12.0 Hz), and Spindle-range (12.0-14.0) frequencies was analyzed during the 1-min preceding the onset of stimulation and the 1-min PSI's.
  
  
  RESULTS
  As hypothesized, power reduction due to stimulation positively correlated with reduction in word-pair recall post-nap specifically for Slow (P < 0.0022) and Delta (P < 0.037) frequency bands.
  
  
  CONCLUSIONS
  These results provide preliminary evidence suggesting a causal and specific role of SWA in declarative memory consolidation during nap.
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK; University College London Medical School, Gower Street, London WC1E 6BT, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Garside
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK; National Institute of Mental Health, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892, USA. Electronic address: Joseph.Arizpe.10@ucl.ac.uk.
authors.forename: Joseph
authors.initials: J
authors.lastname: Arizpe
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK; Department of Neurology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan.
authors.forename: Chi-Ieong
authors.initials: CI
authors.lastname: Lau
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK.
authors.forename: Crystal
authors.initials: C
authors.lastname: Goh
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK.
authors.forename: Vincent
authors.initials: V
authors.lastname: Walsh
mesh_terms: D001245:Association Learning / Q000502:physiology; D001921:Brain / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D000069077:Memory Consolidation / Q000502:physiology*; D012890:Sleep / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation; D055815:Young Adult
keywords: Declarative memory; Delta wave; Memory consolidation; Montage; Nap; Oscillations; Sleep; Slow wave sleep; tACS