title: Recurrence quantification analysis of surface electromyogram supports alterations in motor unit recruitment strategies by anodal transcranial direct current stimulation.
abstract: OBJECTIVE
  Recent evidence indicates that anodal transcranial direct current stimulation (tDCS) can selectively alter the EMG/force relationship of agonist arm muscles; however, the mechanisms mediating those changes are less clear. The purpose of this study was to evaluate the effect of anodal tDCS on motor unit synchronization by using a sophisticated non-linear EMG analysis called recurrence quantification analysis (RQA).
  
  
  METHODS
  Surface EMG signals were collected from the biceps brachii muscle of eighteen healthy young adults (9 tDCS and 9 control) at various force levels (12.5%, 25%, 37.5%, and 50% maximum) before and after the application of anodal tDCS over the primary motor cortex. RQA was employed to quantify the changes in percentage of determinism (% DET) and laminarity (% LAM) of the surface EMG signals, which are surrogate measures of motor unit synchronization.
  
  
  RESULTS
  RQA analyses indicated that the changes in % DET and % LAM scores were significantly higher in the tDCS group than in the control group (p < 0.05) and this effect was particularly pronounced at higher force levels.
  
  
  CONCLUSIONS
  The results of this study provide novel evidence supporting that anodal tDCS significantly alters motor unit firing strategies (i.e., the degree of synchronization) of the biceps brachii muscle.
authors: DEMAR team of INRIA, Université de Montpellier, CNRS, Montpellier Cedex 5, France.
authors: Anirban
authors: A
authors: Dutta
authors: Neuromuscular and Rehabilitation Robotics Laboratory (NeuRRO Lab), Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, MI, USA.|Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
authors: Chandramouli
authors: C
authors: Krishnan
authors: Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.|Moss Rehabilitation Research Institute, Elkins Park, PA, USA.
authors: Shailesh S
authors: SS
authors: Kantak
authors: Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.|Department of Kinesiology, Michigan State University, East Lansing, MI, USA.
authors: Rajiv
authors: R
authors: Ranganathan
authors: Department of Clinical Neurophysiology, University Medical Center, Göttingen, Germany.
authors: Michael A
authors: MA
authors: Nitsche
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology*; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D017711:Nonlinear Dynamics; D065908:Transcranial Direct Current Stimulation / Q000379:methods*
keywords: Recurrence analysis; brain stimulation; electromyography; motor unit; nonlinear analysis; synchronization