The role of gamma and alpha oscillations for blocking out distraction

Although alpha activity (10 Hz) is by far the strongest signal produced by the human brain, it has for decades been considered to reflect rest or idling. However, recent studies have clearly demonstrated that alpha activity plays a pivotal role for cognitive processing. Gamma oscillations (> 30 Hz) and their role for cognition have also been the subject of intensive research. While gamma activity is thought to reflect functional processing, alpha oscillations are now thought to reflect functional inhibition in order to suppress the processing of distracting information. In our recent magnetoencephalography study we found that both power and phase of posterior alpha oscillations are top-down modulated in order to prevent the incorporation of predictable distracters in working memory. We further discuss these results here. We additionally show that the processing of the distracters is clearly distinguishable from the processing of the items to be remembered. The former induced a weaker gamma power and evoked a higher alpha activity. The higher the evoked alpha activity, the better the efficiency of distracter suppression which also depends on the pre-distracter alpha power and phase adjustment. Altogether, these results emphasize the protecting role of alpha activity and its remarkable flexibility. This ability to inhibit distracter information is crucial in our complex environment, as illustrated by the difficulties encountered by patients suffering from attentional disorders.