The centrifugal effect and other spatial artifacts of topographic EEG mapping.

Topographic maps of EEG can contain artifacts that are foreign to clinical electroencephalographers trained to read traditional EEG records. Several spatial artifacts are described and discussed here, including the centrifugal effect, ring enhancement, spatial aliasing, electrode hills and holes, color-step effects, and restriction of minima/maxima to electrode sites. Users of quantitated EEG with topographic maps should be aware of these artifacts and should have a high suspicion for other analogous artifactual spatial phenomena when interpreting individual patient records.