Effects of modeling errors and EEG measurement montage on source localization accuracy

The location of an electrical source in the brain can be determined from the EEGs the source produces on the scalp by calculating the location of a source in a model of the head using the EEGs. Modeling errors produced by differences between the actual head and the head model cause localization errors (i.e., errors in the calculated location of the source). This is a study of the localization errors caused by modeling errors produced by the differences between two features of actual head geometry and a spherical head model. The two features are general nonspherical head shape and the brain pan (i.e., the very nonspherical lower surface of the brain cavity). This is also a study of the localization accuracy of different EEG measurement montages when these modeling errors are present. It has been found that general nonspherical head shape causes maximum localization errors of approximately 1 cm, and that these errors are not very dependent on source location or orientation, or EEG montage. The localization errors caused by the brain pan are generally larger: The maximum error is approximately 2 cm. These errors are very dependent on source location and orientation, and EEG montage. The largest errors occur for sources close to and pointing toward the brain pan surface. These errors also vary widely with montage: A referential montage with the reference point on the bottom of the model has the largest errors. Referential montages with reference points on the side or top of the model, an average reference montage, or a bipolar montage generally produce much smaller errors.