Eccles and Walter (1950) both agree that Alpha is the brain's scanning mechanism. In light of logic and current neurophysiological information, this makes sense. For example, when the eyes are closed and the visual centers in the occipital and parietal regions are deprived of visual stimuli, Alpha amplitude in the posterior head regions usually increases dramatically. Furthermore, Galin and Omstein (1972) found Alpha magnitude decreases over the hemisphere of the brain that is under task.
Alpha rhythm, then, appears to be only indirectly involved in the brain's attentional mechanism. Alpha is the brain's scanning (idling) frequency, denoting a brain "standing by," waiting to give way to Beta should attention be required, or to be the bridge, the gate, to Theta and Delta for drowsiness, sleep, and certain cognitive challenges. Alpha is therefore an important cerebral rhythm, perhaps being mathematically a resonant piece of the 40-Hz Grand Conductor's ensemble of frequencies.