EEG laterality in the era of structural brain imaging.

Bilateral EEG recording is a common practice when brain laterality needs to be assessed in cognitive neurophysiology and psychiatry research. Its precision and validity remain uncertain. With structural brain imaging methods, it is possible to examine EEG electrode placements according to the 10-20 system and the validity of inferences made on derived data. Frequent sources of placement errors are examined along with important factors that contribute to EEG imbalance. Examples are mentioned where asymmetries of EEG/ERP caused by cranial and parenchymal brain asymmetries may be mistaken for cognition-related laterality changes. Because external skull landmarks are not reliable predictors of cranial and parenchymal brain asymmetries, laterality assessment cannot be guaranteed by the 10-20 system. Consequently, a return, on a case-to-case basis, to nonstandard montages, assisted by structural brain imaging is seen as an acceptable alternative.