Bilateral alpha distribution and anatomic brain asymmetries

The parieto-occipital (PO) index of the VEP alpha-afterdischarge (AD) was assessed bilaterally in normal subjects in three successive sessions separated by one-three weeks with two within-session retests. Correlations between PO values and asymmetries of occipital and parietal width, mastoid area, basal angle, cephalic, and plagiocephaly indices were established in simple correlation and stepwise multiple regression analysis. Occipital width, notably in the right hemisphere correlated reliably with the PO index in relaxed wakefulness and the vigilance task. The population having normal and reversed occipital brain width is predicted to have different parieto-occipital AD distribution. Some errors of lateral EEG measurements introduced by slant cranial deformity are discussed in order to call attention to the fact that anatomy-related lateral EEG changes may masquerade as cognition-related asymmetries.