Individual differences in anterior EEG asymmetry: methodological problems and solutions.

In the last two decades, a substantive body of empirical work investigated the association between individual differences of electroencephalogram (EEG) alpha asymmetry and affective/motivational dispositions. Recent work indicated that several methodological problems persist in this field. The present paper reviews these problems with a focus on the reliability and validity of measures of anterior resting EEG asymmetry, which serve as a proxy for trait-like asymmetries of cortical activity. These issues include the treatment of ocular and muscle artifacts, the choice of the EEG reference, the use of current source density (CSD) measures, the state-trait nature of resting asymmetry, and the treatment of state-like fluctuations of the measures. In addition, the statistical problem of inflated type-I error due to multiple testing is also considered and different approaches to counteract this problem are suggested.