title: The interaction with task-induced activity is more important than polarization: a tDCS study.
abstract: BACKGROUND
  Anodal transcranial direct current stimulation (A-tDCS) is a non-invasive technique in which cortical polarization can be used to increase excitability and facilitate learning through the modulation of neuroplasticity. Although the facilitatory effects of A-tDCS are well documented, there is evidence that they are not always present and may even be reversed during task execution.
  
  
  OBJECTIVE
  In this study, we explored the interaction between A-tDCS and task execution. We aimed to test how the excitability induced by the task interacts with the excitability induced by A-tDCS and determines the behavioral outcome.
  
  
  METHODS
  We performed an experiment in which A-tDCS or a control stimulation (Ctrl) were combined with one of two motor practices (MP), one inducing learning and increasing cortical excitability (F-MP) and the other neither inducing learning nor changing cortical excitability (S-MP). Six blocks of MP were performed while the primary motor cortex was stimulated. Moreover, one block of F-MP was performed before the stimulation (baseline) and one after. In an additional experiment, motor evoked potentials (MEPs) were recorded before the baseline block (TMS-pre) and after the MP (TMS-post).
  
  
  RESULTS
  We observed that A-tDCS reduced learning when participants performed the F-MP and facilitated learning for the S-MP. MEPs data paralleled behavioral results, confirming that the effects generated by A-tDCS depend on the excitability changes induced by the task.
  
  
  CONCLUSIONS
  Our results demonstrate that tDCS-induced plasticity is task-dependent, and the concurrent combination of A-tDCS with another excitability-increasing event, e.g., motor practice, may trigger non-additive mechanisms, hindering neuroplasticity.
authors.affiliation: Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Via Pilastroni 4, 25125 Brescia, Italy. Electronic address: marta.bortoletto@cognitiveneuroscience.it.
authors.forename: Marta
authors.initials: M
authors.lastname: Bortoletto
authors.affiliation: Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Via Pilastroni 4, 25125 Brescia, Italy.
authors.forename: Maria Concetta
authors.initials: MC
authors.lastname: Pellicciari
authors.affiliation: Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Via Pilastroni 4, 25125 Brescia, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Rodella
authors.affiliation: Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Via Pilastroni 4, 25125 Brescia, Italy; Neuroscience Section, Department of Clinical and Experimental Sciences, University of Brescia, 25123 Brescia, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Miniussi
mesh_terms: D000293:Adolescent; D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D011214:Practice, Psychological; D011597:Psychomotor Performance / Q000502:physiology; D065908:Transcranial Direct Current Stimulation; D055815:Young Adult
keywords: Cortical plasticity; Motor learning; Noise; Non-invasive brain stimulation (NIBS); State-dependent; Transcranial direct current stimulation