title: Transcranial direct current stimulation over multiple days improves learning and maintenance of a novel vocabulary.
abstract: BACKGROUND
  Recently, growing interest emerged in the enhancement of human potential by means of non-invasive brain stimulation. In particular, anodal transcranial direct current stimulation (atDCS) has been shown to exert beneficial effects on motor and higher cognitive functions. However, the majority of transcranial direct current stimulation (tDCS) studies have assessed effects of single stimulation sessions that are mediated by transient neural modulation. Studies assessing the impact of multiple stimulation sessions on learning that may induce long-lasting behavioural and neural changes are scarce and have not yet been accomplished in the language domain in healthy individuals.
  
  
  METHODS
  The present study probed the potential of atDCS to enhance language learning over multiple days by employing an explicit word learning paradigm. Forty healthy young participants were randomized to learning with either simultaneous atDCS or sham stimulation (N = 20/group; comparable regarding demographic variables and neurocognitive status). All participants acquired a novel vocabulary (familiar and novel object picture - non-word pairs) over five consecutive days. Two memory tasks (free recall; forced choice recognition tasks) were administered immediately after each training session. A one week follow-up tested the maintenance of learning success.
  
  
  RESULTS
  Linear mixed effects model analysis revealed superior learning during atDCS compared to sham stimulation for both familiar and novel objects. atDCS yielded a steeper learning curve and significantly more pronounced learning at the end of the training during the recall task. During the recognition task, the atDCS group reached ceiling levels earlier and overall learning success was greater. For both tasks, beneficial atDCS effects were maintained during the follow-up assessment.
  
  
  CONCLUSIONS
  The present study provides direct evidence that atDCS administered during multiple learning sessions facilitates language learning and that effects are maintained over time. This study contributes important novel information about the extent of stimulation effects in the healthy brain, thereby highlighting the potential of atDCS to enhance language recovery after stroke.
authors.affiliation: Department of Neurology, Charité University Medicine, Berlin, Germany; Center for Stroke Research, Charité University Medicine, Berlin, Germany; Center for Clinical Research, University of Queensland, Brisbane, Australia. Electronic address: m.meinzer@uq.edu.au.
authors.forename: Marcus
authors.initials: M
authors.lastname: Meinzer
authors.affiliation: Department of Neurology, Charité University Medicine, Berlin, Germany.
authors.forename: Sophia
authors.initials: S
authors.lastname: Jähnigen
authors.affiliation: Center for Clinical Research, University of Queensland, Brisbane, Australia; CCRE in Aphasia Rehabilitation, University of Queensland, Brisbane, Australia.
authors.forename: David A
authors.initials: DA
authors.lastname: Copland
authors.affiliation: Department of Neurology, Charité University Medicine, Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Darkow
authors.affiliation: Center for Stroke Research, Charité University Medicine, Berlin, Germany; Department for Biostatistics and Clinical Epidemiology, Charité University Medicine, Berlin, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Grittner
authors.affiliation: Department of Neurology, Charité University Medicine, Berlin, Germany.
authors.forename: Keren
authors.initials: K
authors.lastname: Avirame
authors.affiliation: Center for Clinical Research, University of Queensland, Brisbane, Australia; CCRE in Aphasia Rehabilitation, University of Queensland, Brisbane, Australia.
authors.forename: Amy D
authors.initials: AD
authors.lastname: Rodriguez
authors.affiliation: Department of Neurology, Charité University Medicine, Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Lindenberg
authors.affiliation: Department of Neurology, Charité University Medicine, Berlin, Germany; Center for Stroke Research, Charité University Medicine, Berlin, Germany; NeuroCure Cluster of Excellence, Charité University Medicine, Berlin, Germany. Electronic address: agnes.floeel@charite.de.
authors.forename: Agnes
authors.initials: A
authors.lastname: Flöel
mesh_terms: D000293:Adolescent; D000328:Adult; D000339:Affect; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008568:Memory / Q000502:physiology; D011939:Mental Recall / Q000502:physiology; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology; D011932:Reading; D016037:Single-Blind Method; D014706:Verbal Learning / Q000502:physiology*; D014825:Vocabulary; D055815:Young Adult
keywords: Brain stimulation; Language functions; Learning; Longitudinal design; Transcranial direct current stimulation