title: Surface Laplacian of scalp electrical signals and independent component analysis resolve EMG contamination of electroencephalogram.
abstract: The serious impact of electromyogram (EMG) contamination of electroencephalogram (EEG) is well recognised. The objective of this research is to demonstrate that combining independent component analysis with the surface Laplacian can eliminate EMG contamination of the EEG, and to validate that this processing does not degrade expected neurogenic signals. The method involves sequential application of ICA, using a manual procedure to identify and discard EMG components, followed by the surface Laplacian. The extent of decontamination is quantified by comparing processed EEG with EMG-free data that was recorded during pharmacologically induced neuromuscular paralysis. The combination of the ICA procedure and the surface Laplacian, with a flexible spherical spline, results in a strong suppression of EMG contamination at all scalp sites and frequencies. Furthermore, the ICA and surface Laplacian procedure does not impair the detection of well-known, cerebral responses; alpha activity with eyes-closed; ERP components (N1, P2) in response to an auditory oddball task; and steady state responses to photic and auditory stimulation. Finally, more flexible spherical splines increase the suppression of EMG by the surface Laplacian. We postulate this is due to ICA enabling the removal of local muscle sources of EMG contamination and the Laplacian transform being insensitive to distant (postural) muscle EMG contamination.
authors.affiliation: School of Medicine, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; Centre for Neuroscience, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; Medical Device Research Institute, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia. Electronic address: sean.fitzgibbon@flinders.edu.au.
authors.forename: S P
authors.initials: SP
authors.lastname: Fitzgibbon
authors.affiliation: School of Computer Science, Engineering and Mathematics, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia.
authors.forename: D
authors.initials: D
authors.lastname: DeLosAngeles
authors.affiliation: School of Computer Science, Engineering and Mathematics, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; Medical Device Research Institute, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia.
authors.forename: T W
authors.initials: TW
authors.lastname: Lewis
authors.affiliation: School of Computer Science, Engineering and Mathematics, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; Medical Device Research Institute, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; College of Computer Science & Technology, Beijing University of Technology, 100 Ping Le Yuan, Chaoyang District, Beijing 100124, PR China.
authors.forename: D M W
authors.initials: DM
authors.lastname: Powers
authors.affiliation: School of Medicine, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia.
authors.forename: E M
authors.initials: EM
authors.lastname: Whitham
authors.affiliation: School of Medicine, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; Centre for Neuroscience, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia.
authors.forename: J O
authors.initials: JO
authors.lastname: Willoughby
authors.affiliation: School of Computer Science, Engineering and Mathematics, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia; Medical Device Research Institute, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia.
authors.forename: K J
authors.initials: KJ
authors.lastname: Pope
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D001931:Brain Mapping / Q000009:adverse effects; D004569:Electroencephalography; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D010775:Photic Stimulation; D025341:Principal Component Analysis; D012146:Rest; D012535:Scalp / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted
keywords: EEG; Electromyogram; Evoked response; Independent component analysis; Oddball task; Steady state response; Surface Laplacian