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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
Rectification and non-linear pre-processing of EMG signals for cortico-muscular analysis
Journal of Neuroscience Methods, Volume 124, No. 2, Year 2003
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Description
Rectification of the electromyographic (EMG) signal is a commonly used pre-processing procedure that allows detection of significant coherence between EMG and measured cortical signals. However, despite its accepted and wide-spread use, no detailed analysis has been presented to offer insight into the precise function of rectification. We begin this paper with arguments based on single motor unit action potential (AP) trains to demonstrate that rectification effectively enhances the firing rate information of the signal. Enhancement is achieved by shifting the peak of the AP spectrum toward the lower firing rate frequencies, whilst maintaining the firing rate spectra. A similar result is obtained using the analytic envelope of the signal extracted using the Hilbert transform. This argument is extended to simulated EMG signals generated using a published EMG model. Detection of firing rate frequencies is obtained using phase randomised surrogate data, where the original EMG power spectrum exceeds the averaged rectified surrogate spectra at integer multiples of firing rate frequencies. Model simulations demonstrate that this technique accurately determines grouped firing rate frequencies. Extraction of grouped firing rate frequencies prior to coherency analyses may further aid interpretation of significant cortico-muscular coherence findings. © 2003 Elsevier Science B.V. All rights reserved.
Authors & Co-Authors
Myers, Lance J.
Ireland, Dublin
University College Dublin
Lowery, Madeleine M.
United States, Evanston
Northwestern University
O'Malley, Mark J.
Ireland, Dublin
University College Dublin
Vaughan, Christopher L.
South Africa, Cape Town
University of Cape Town
Heneghan, C.
Ireland, Dublin
University College Dublin
St.Clair Gibson, Allan
United States, Bethesda
National Institute of Neurological Disorders and Stroke
Harley, Yolande X.R.
South Africa, Cape Town
University of Cape Town
Sreenivasan, R.
South Africa, Cape Town
University of Cape Town
Statistics
Citations: 289
Authors: 8
Affiliations: 4
Identifiers
Doi:
10.1016/S0165-0270(03)00004-9