Hemispheric asymmetries in the EEG: Is there an association between N1 lateralization and alpha asymmetry?

Several cognitive systems in the human brain, such as language and face processing, are organized asymmetrically. One of the primary neuroscientific methods to assess such functional hemispheric asymmetries is electroencephalography (EEG). The two major forms of analyzing asymmetries in the EEG signal are event-related potentials (ERPs), such as the N1, and oscillations, such as the alpha band. However, the relationships between these two forms of EEG asymmetries are not well understood. Therefore, it was the aim of the present study to (1) replicate previous results on N1 and alpha band asymmetries and (2) assess whether they show a negative correlation with each other, as could be expected from the hypothesis that alpha represents an absence of cognition. To this end, we tested n = 100 left-, mixed-, and right-handed participants with EEG Resting-State, as well as task-based EEG with words, faces, emotional faces, and houses as stimuli. Replication of previous EEG asymmetry findings showed mixed results. Interestingly, we found strong positive associations between individual ERP and alpha band asymmetries. This finding highlights the need to reassess the functional role of alpha asymmetries and suggests that they do not only reflect the absence of cognition but also reflect active neuronal processing asymmetries.