Time-Dependent Cortical Activation in Voluntary Muscle Contraction

Qi Yang 1, 4, Xiaofeng Wang 3, Yin Fang 1, Vlodek Siemionow 1, 2, Wanxiang Yao 5, Guang H Yue*, 1, 2, 4
1 Departments of Biomedical Engineering, The Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
2 Departments of Physical Medicine and Rehabilitation, The Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
3 Departments of Quantitative Health Sciences, The Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
4 Department of Chemical and Biomedical Engineering, Cleveland State University, Cleveland, Ohio 44115, USA
5 Department of Health and Kinesiology, University of Texas at San Antonio, San Antonio, TX 78249, USA

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open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (, which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Department of Biomedical Engineering, The Cleveland Clinic, 9500 Euclid Avenue, ND20, Cleveland, OH 44195, USA; Tel: (216) 4459336; Fax: (216) 444-9198; E-mail:


This study was to characterize dynamic source strength changes estimated from high-density scalp electroencephalogram (EEG) at different phases of a submaximal voluntary muscle contraction. Eight healthy volunteers performed isometric handgrip contractions of the right arm at 20% maximal intensity. Signals of the handgrip force, electromyography (EMG) from the finger flexor and extensor muscles and 64-channel EEG were acquired simultaneously. Sources of the EEG were analyzed at 19 time points across preparation, execution and sustaining phases of the handgrip. A 3-layer boundary element model (BEM) based on the MNI (Montréal Neurological Institute) brain MRI was used to overlay the sources. A distributed current density model, LORETA L1 norm method was applied to the data that had been processed by independent component analysis (ICA). Statistical analysis based on a mixed-effects polynomial regression model showed a significant and consistent time-dependent non-linear source strength change pattern in different phases of the handgrip. The source strength increased at the preparation phase, peaked at the force onset time and decreased in the sustaining phase. There was no significant difference in the changing pattern of the source strength among Brodmann’s areas 1, 2, 3, 4, and 6. These results show, for the first time, a high time resolution increasing-and-decreasing pattern of activation among the sensorimotor regions with the highest activity occurs at the muscle activity onset. The similarity in the source strength time courses among the cortical centers examined suggests a synchronized parallel function in controlling the motor activity.

Keywords: EEG source, Current density reconstruction, Electroencephalography (EEG), Brain, Handgrip force, Voluntary muscle contraction.