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Rectification and non-linear pre-processing of EMG signals for cortico-muscular analysis
L J Myers1, M Lowery, M O'Malley
1Department of Electronic and Electrical Engineering, University College Dublin, 4, Dublin, Ireland. lance@beach.co.za
Journal of Neuroscience Methods
|April 23, 2003
Summary
Rectification of electromyographic (EMG) signals enhances firing rate information by shifting power spectrum peaks. This pre-processing technique aids in interpreting cortico-muscular coherence findings.
Area of Science:
- Neuroscience
- Biomedical Engineering
- Signal Processing
Background:
- Rectification is a standard pre-processing step for electromyographic (EMG) signals.
- Its precise functional role in analyzing cortico-muscular coherence remains unclear.
Purpose of the Study:
- To analyze the functional impact of EMG signal rectification.
- To investigate how rectification affects firing rate information and its utility in cortico-muscular coherence studies.
Main Methods:
- Analysis of single motor unit action potential (AP) trains.
- Application of the Hilbert transform to extract the analytic envelope.
- Simulation of EMG signals using a published EMG model.
- Utilizing phase-randomized surrogate data for spectral analysis.
Main Results:
- Rectification shifts the power spectrum peaks of AP trains toward lower frequencies, enhancing firing rate information.
- The analytic envelope method yields similar results to rectification.
- Simulations confirm that rectification accurately identifies grouped firing rate frequencies.
Conclusions:
- Rectification effectively enhances the detection of firing rate information within EMG signals.
- Extracting firing rate frequencies before coherency analysis can improve the interpretation of cortico-muscular coherence.
- This study provides a detailed analysis of EMG rectification's function.