Alpha Rhythms

Abstract

Ensembles of synchronously active cortical neurons generate electromagnetic field potentials that can be measured by electroencephalography (EEG) or magnetoencephalography (MEG). The alpha frequency band is defined to be between 8 and 13 Hz (Berger, 1929). The classical alpha rhythm is prominent at electrodes overlying the occipital (visual) cortex and to a lesser extent over the posterior temporal and parietal areas. Alpha rhythm occurs in a condition of relaxed wakefulness with eyes closed. The alpha rhythm disappears gradually during drowsiness, and different types of alpha activity appear in rapid eye movement (REM) sleep.