Recurrence quantification analysis of surface electromyogram supports alterations in motor unit recruitment strategies by anodal transcranial direct current stimulation

Article type: Research Article

Authors: Dutta, Anirban^{a; 1} | Krishnan, Chandramouli^{b; c; *; 1} | Kantak, Shailesh S.^{c; d} | Ranganathan, Rajiv^{c; e} | Nitsche, Michael A.^f

Affiliations: [a] DEMAR team of INRIA, Université de Montpellier, CNRS, Montpellier Cedex 5, France | [b] Neuromuscular and Rehabilitation Robotics Laboratory (NeuRRO Lab), Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, MI, USA | [c] Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, Chicago, IL, USA | [d] Moss Rehabilitation Research Institute, Elkins Park, PA, USA | [e] Department of Kinesiology, Michigan State University, East Lansing, MI, USA | [f] Department of Clinical Neurophysiology, University Medical Center, Göttingen, Germany

Correspondence: [*] Corresponding author: Dr. Chandramouli Krishnan, Department of Physical Medicine & Rehabilitation, University of Michigan, 325 E Eisenhower Parkway, Suite 3013, Ann Arbor,MI 48108, USA. Tel.: +1 319 321 0117; mouli@umich.edu

Note: [1] Indicates equal contribution.

Abstract: Purpose: 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. Conclusion: 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.

Keywords: Recurrence analysis, electromyography, nonlinear analysis, brain stimulation, motor unit, synchronization

DOI: 10.3233/RNN-140469

Journal: Restorative Neurology and Neuroscience, vol. 33, no. 5, pp. 663-669, 2015