The alpha rhythm of the electroencephalogram (EEG) is a non-invasive and cost-effective index of the tonic state of the brain. The classical view of resting EEG alpha is of a posterior1, 8–13 Hz idling rhythm characteristic of a relaxed, wakeful state, which is blocked (desynchronized) when the individual is alert, or when visual processes are engaged by opening the eyes. An inverse association has been reported between scalp-recorded EEG alpha and local PET perfusion (3). Feige et al. (4) also reported an inverse association between posterior alpha (quantified by independent components analysis) and the fMRI BOLD response in cortical visual regions, but not in subcortical visual or reticular thalamic nuclei, which have also been implicated in the generation and synchronization of alpha (5–8). Alpha is also generated within the ventral visual stream, although its laminar organization differs considerably across cortical regions (9).
