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Electric Fields of the BrainThe neurophysics of EEG$
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Paul L. Nunez and Ramesh Srinivasan

Print publication date: 2006

Print ISBN-13: 9780195050387

Published to Oxford Scholarship Online: May 2009

DOI: 10.1093/acprof:oso/9780195050387.001.0001

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Recording Strategies, Reference Issues, and Dipole Localization

Recording Strategies, Reference Issues, and Dipole Localization

(p.275) 7 Recording Strategies, Reference Issues, and Dipole Localization
Electric Fields of the Brain

Paul L. Nunez

Ramesh Srinivasan

Oxford University Press

Every EEG measurement depends on the locations of the recording and so-called reference electrode. The measured potential difference is a property of the path between electrode pairs. This applies to any reference including the linked-ears (or linked-mastoid) reference. The physical linked-ears reference provides an unbalanced “random” reference. The mathematical linked-ears reference offers no obvious advantages over other references. The average reference can be used to approximate reference independent potentials if used with a large number of electrodes, but is still biased by the limited sampling of potentials over the lower surface of the head. Regardless of source, the EEG is a low-pass spatially filtered signal, making discrete sampling of the potential distribution feasible without spatial aliasing. Modern EEG systems have facilitated spatial mapping of EEG potentials. Any potential distribution on the scalp can be fit (in a least-squared sense) by an equivalent dipole distribution by solving the inverse problem.

Keywords:   reference electrode, average reference, linked-ears reference, linked-mastoids reference, spatial filter, inverse problem, source localization

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