EMG Rectification Is Detrimental for Identifying Abnormalities in Corticomuscular and Intermuscular Coherence in Spinocerebellar Ataxia Type 2

Abstract

Corticomuscular and intermuscular coherence (CMC, IMC) reflect connectivity between neuronal activity in the motor cortex measured by electroencephalography (EEG) and muscular activity measured by electromyography (EMG), or between activity in different muscles, respectively. There is an ongoing debate on the appropriateness of EMG rectification prior to coherence estimation. This work examines the effects of EMG rectification in CMC and IMC estimation in 20 spinocerebellar ataxia type 2 (SCA2) patients, 16 prodromal SCA2 gene mutation carriers, and 26 healthy controls during a repetitive upper or lower limb motor task. Coherence estimations were performed using the non-rectified raw EMG signal vs. the rectified EMG signal. EMG rectification decreases the level of significance of lower beta-frequency band CMC and IMC values in SCA2 patients and prodromal SCA2 mutation carriers vs. healthy controls, and also results in overall lower coherence values. EMG rectification is detrimental for beta-frequency band CMC and IMC estimation. One likely reason for this effect is distortion of coherence estimation in high-frequency signals, where the level of amplitude cancelation is high.

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Acknowledgments

A preliminary version of this manuscript has been published in a book representing the collection of lectures of the Iberoamerican Congress on Pattern Recognition (CIARP 2019, 28–31 October 2019, Havana, Cuba): Ruiz-Gonzalez Y, Velázquez-Pérez L, Rodríguez-Labrada R, Torres-Vega R, Ziemann U (2019) Role of EMG Rectification for Corticomuscular and Intermuscular Coherence Estimation of Spinocerebellar Ataxia Type 2 (SCA2). In: Nyström I, Hernández Heredia Y, Milián Núñez V (eds.) Progress in Pattern Recognition, Image Analysis, Computer Vision, and Applications. CIARP 2019. Lecture Notes in Computer Science, vol 11896. Springer, Cham. We are grateful to the SCA2 patients, prodromal SCA2 mutation carriers, and the healthy controls for their participation.

Funding

This work was carried out while Prof. Luis Velázquez-Pérez was the recipient of a Georg Forster Research Award from the Alexander von Humboldt Foundation (3.4 – KUB/1149891), which funded this research project together with the Cuban Ministry of Public Health. LVP is the Editor-in-Chief of Anales de la Academia de Ciencias de Cuba, Associate Editor of Cerebellum and Ataxias, and Associate Editor of Investigation en Discapacidad. He received grants from the Cuban Ministry of Public Health, and the German Ministry of Education and Research. UZ is the Editor-in-Chief of Clinical Neurophysiology, Deputy Editor of Brain Stimulation, and editorial board member of The Journal of Neuroscience, Experimental Brain Research, Neurological Research and Practice, Nervenarzt. He received grants from the European Research Council, German Research Foundation, German Ministry of Education and Research, Biogen Idec GmbH, Servier, and Janssen Pharmaceuticals NV, and consulting fees from Biogen Idec GmbH, Bayer Vital GmbH, Bristol Myers Squibb GmbH, Pfizer, CorTec GmbH, Medtronic GmbH, all not related to this work.

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Ruiz-Gonzalez, Y., Velázquez-Pérez, L., Rodríguez-Labrada, R. et al. EMG Rectification Is Detrimental for Identifying Abnormalities in Corticomuscular and Intermuscular Coherence in Spinocerebellar Ataxia Type 2. Cerebellum (2020). https://doi.org/10.1007/s12311-020-01149-z

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Keywords

  • Corticomuscular coherence
  • Intermuscular coherence
  • EEG
  • EMG
  • EMG rectification
  • Spinocerebellar ataxia type 2