Wavelike Properties of the Alpha Rhythm

Apparent similarities between brain waves and physical waves are considered. The distribution of power in the alpha rhythm over frequency and spatial wavelength is measured in several subjects. This is accomplished by means of spatial-temporal Fourier analyses of scalp surface potentials using multichannel recordings from electrodes placed along the midline. It is found that the spectrum of midline alpha oscillations peaks for long wavelengths (≃20 cm). A dispersion relation relating frequency to spatial wavelength apparently exists for frequencies near the peak alpha frequency. That is, in all 13 records, frequency components just above the peak alpha frequency have shorter midline wavelengths than low alpha frequency components. The relationship of these results to theoretical descriptions of the EEG and to other experiments is discussed.