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 analyzing asymmetries in specific event-related potentials (ERP), such as the N1, and analyzing asymmetries in event-related or resting state EEG oscillations such as in 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 replicate previous results on ERP and alpha band asymmetries and 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 participants with EEG RS, 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 re-assess the functional role of alpha asymmetries and suggests that they do not only reflect the absence of cognition as widely assumed but reflect active neuronal processing asymmetries such as in phase reorganization and the timing of neural activity.