Mechanisms of selective inhibition in visual spatial attention are indexed by alpha-band EEG synchronization

Electroencephalographic studies in humans have demonstrated that orienting of visual attention induces a decrease in oscillatory alpha-band activity (alpha-desynchronization) over cortical areas tuned to the attended visual space. This is interpreted as reflecting intentionally enhanced excitability of these areas to facilitate upcoming visual processing. However, the inverse mechanism might also apply. Brain areas that process task-irrelevant space might be actively suppressed by increased alpha-activity (alpha-synchronization) to protect against input of distracter information. In the present study, we demonstrate that such suppression mechanisms are highly selective and are taking place even without distracters that need to be ignored. During voluntary orienting of attention, we found alpha-synchronization to dominate over desynchronization, to be topographically specific for each of eight attention positions, and to occur over areas processing unattended space in a retinotopically organized pattern. This indicates that alpha-synchronization is an important component of selective attention, serving active suppression of unattended positions during visual spatial orienting.