Asymmetry of Occipital Alpha-Rhythm under Resting Conditions: A Neurophysiological Measure of “Hemisphericity”

Abstract

Using the resting EEGs of 20 healthy subjects in semi-recumbent position with eyes dosed and left undisturbed, we studied the question whether and, if so, to what extent, lateralization of occipital alpha-rhythm depends on level of vigilance. As a simple indicator of vigilance, the relative alpha-power for each 2-sec. epoch of 02-CZ (occipital right) was calculated. Lateralization was defined as the ratio of absolute alpha-powers in 01-CZ and 02-CZ (occipital left and right). This was also calculated epoch by epoch. The results of individual analysis of data from each subject allowed categorization into 3 types. This typological differentiation obtained quantitatively could be supported by visual pattern analysis. The findings are discussed in relation to the state- vs trait-problem which constantly confronts us when we interpret experimentally obtained functional asymmetries of hemispheres.