title: The spatial location of EEG electrodes: locating the best-fitting sphere relative to cortical anatomy.
abstract: The location of the international 10-20 system electrode positions and 14 fiducial landmarks are described in cartesian coordinates (+/- 1.4 mm average accuracy). Six replications were obtained on 3 separate days from 4 normal subjects, who were compared to each other with a best-fit sphere algorithm. Test-retest reliability depended on the electrode position: the parasagittal electrodes were associated with greater measurement errors (maximum 7 mm) than midline locations. Location variability due to head shape was greatest in the temporal region, averaging 5 mm from the mean. For each subject's electrode locations a best-fitting sphere was determined (79-87 mm radius, 6% average error). A surface-fitting algorithm was used to transfer the electrode locations and best-fitting sphere to MR images of the brain and scalp. The center of the best-fitting sphere coincided with the floor of the third ventricle 5 mm anterior to the posterior commissure. The melding of EEG electrode location information with brain anatomy provides an empirical basis for associating hypothetical equivalent dipole locations with their anatomical substrates.
authors.affiliation: Department of Neurology, University of Chicago, IL 60637.
authors.forename: V L
authors.initials: VL
authors.lastname: Towle
authors.forename: J
authors.initials: J
authors.lastname: Bolaños
authors.forename: D
authors.initials: D
authors.lastname: Suarez
authors.forename: K
authors.initials: K
authors.lastname: Tan
authors.forename: R
authors.initials: R
authors.lastname: Grzeszczuk
authors.forename: D N
authors.initials: DN
authors.lastname: Levin
authors.forename: R
authors.initials: R
authors.lastname: Cakmur
authors.forename: S A
authors.initials: SA
authors.lastname: Frank
authors.forename: J P
authors.initials: JP
authors.lastname: Spire
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology; D001931:Brain Mapping; D004566:Electrodes; D004569:Electroencephalography / Q000295:instrumentation*; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010775:Photic Stimulation