Phase relationships of alpha rhythm in man

Stationary phase relationships of human scalp EEGs in the frequency range of the alpha rhythm were examined by the method of cross-spectral analysis. EEGs were recorded from midsaggital points equally spaced on the scalp in normal and blind adults. Cross-spectral analysis was applied to one- or three-minute records and to successive q0-second records. The generalized component, which usually formed a dominant peak in the EEG spectra, showed a gradual phase advance toward the frontal region but seldom reached 180 degrees, and the phase shift at intermediate points was not linearly related to the distance between them. A parallel relation was confirmed between the increase in the inter-regional phase difference and the decrease in the coherence value. A variety of phase differences was noticed for the more localized subordinate component, and the angles of this component ranged more broadly than with the generalized dominant component. Phase relations of the alpha rhythm in the blind were similar to those of the localized component in normal subjects. Thus, in respect to inter-regional relationships in the antero-posterior direction, the alpha rhythms were classified into at least two types, one closely related to the visual function and the other depending upon some functions other than visual. Effectiveness of the cross-spectral analysis on phase relations of the EEG was discussed in comparison with other methods.