title: Learned EEG-based brain self-regulation of motor-related oscillations during application of transcranial electric brain stimulation: feasibility and limitations.
abstract: OBJECTIVE
  Transcranial direct current stimulation (tDCS) improves motor learning and can affect emotional processing and attention. However, it is unclear whether learned electroencephalography (EEG)-based brain-machine interface (BMI) control during tDCS is feasible, how application of transcranial electric currents during BMI control would interfere with feature-extraction of physiological brain signals and how it affects brain control performance. Here we tested this combination and evaluated stimulation-dependent artifacts across different EEG frequencies and stability of motor imagery-based BMI control.
  
  
  METHODS
  Ten healthy volunteers were invited to two BMI-sessions, each comprising two 60-trial blocks. During the trials, learned desynchronization of mu-rhythms (8-15 Hz) associated with motor imagery (MI) recorded over C4 was translated into online cursor movements on a computer screen. During block 2, either sham (session A) or anodal tDCS (session B) was applied at 1 mA with the stimulation electrode placed 1 cm anterior of C4.
  
  
  RESULTS
  tDCS was associated with a significant signal power increase in the lower frequencies most evident in the signal spectrum of the EEG channel closest to the stimulation electrode. Stimulation-dependent signal power increase exhibited a decay of 12 dB per decade, leaving frequencies above 9 Hz unaffected. Analysis of BMI control performance did not indicate a difference between blocks and tDCS conditions.
  
  
  CONCLUSIONS
  Application of tDCS during learned EEG-based self-regulation of brain oscillations above 9 Hz is feasible and safe, and might improve applicability of BMI systems.
authors.affiliation: Human Cortical Physiology and Neurorehabilitation Section, NINDS, NIH Bethesda, MD, USA ; Applied Neurotechnology Lab, Department of Psychiatry and Psychotherapy, University Hospital Tübingen Tübingen, Germany ; Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen Tübingen, Germany.
authors.forename: Surjo R
authors.initials: SR
authors.lastname: Soekadar
authors.affiliation: Human Cortical Physiology and Neurorehabilitation Section, NINDS, NIH Bethesda, MD, USA ; Applied Neurotechnology Lab, Department of Psychiatry and Psychotherapy, University Hospital Tübingen Tübingen, Germany ; Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen Tübingen, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Witkowski
authors.affiliation: Applied Neurotechnology Lab, Department of Psychiatry and Psychotherapy, University Hospital Tübingen Tübingen, Germany ; Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen Tübingen, Germany.
authors.forename: Eliana G
authors.initials: EG
authors.lastname: Cossio
authors.affiliation: Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen Tübingen, Germany ; Ospedale san Camillo, IRCCS Venice, Italy.
authors.forename: Niels
authors.initials: N
authors.lastname: Birbaumer
authors.affiliation: Human Cortical Physiology and Neurorehabilitation Section, NINDS, NIH Bethesda, MD, USA.
authors.forename: Leonardo G
authors.initials: LG
authors.lastname: Cohen
keywords: EEG; brain-machine interface (BMI) control; motor imagery; stimulation artifacts; transcranial electric stimulation (TES)