NDLI: EEG cohererence and reference signals: experimental results and mathematical explanations

Content Provider	Springer Nature Link
Author	Essl, M. Rappelsberger, P.
Copyright Year	1998
Abstract	Coherence has become an essential tool in the description of functional relationships between EEG signals generated within various brain areas. In EEG coherence analysis, the reference signal has an important influence, as an improper reference can distort the results and make them impossible to interpret. In the study, EEG are recorded from one volunteer in 11 sessions, with electrodes selected according to the international 10–20 system against FC$_{z}$. Additional electrodes are placed on the nose, chin and left and right ear lobes, and recordings are made also against FC$_{z}$. This enables re-referencing of the stored EEG signals for different reference sites, averaged reference signals, common average reference, Laplacian and bipolar. Coherence values using single reference electrodes depend on the reference site to a large extent. Reliable results are obtained using averaged non-cephalic signals as reference ([A$_{1}$+A$_{2}$]/2). Coherence based on FC$_{z}$ yields slightly lower or higher values than that based on non-cephalic reference sites. Completely different results yield common average reference recordings, Laplacian and bipolar recordings, probably owing to the cancellation effect of essential signal portions using these techniques. A mathematical model for coherence based on signal-to-noise ratios is introduced to explain the experimental findings: the model demonstrates that noisy reference signals lead to coherence increase, whereas a coherent amount in the reference signal leads to coherence decrease.
Starting Page	399
Ending Page	406
Page Count	8
File Format	PDF
ISSN	01400118
Journal	Medical and Biological Engineering and Computing
Volume Number	36
Issue Number	4
e-ISSN	17410444
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	1998-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	EEG coherence Reference recording Common average reference Bipolar Laplacian Coherence model Human Physiology Neurosciences Imaging Radiology Computer Applications Biomedical Engineering
Content Type	Text
Resource Type	Article
Subject	Biomedical Engineering Computer Science Applications

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