Analysis of Wave Shapes of α Waves on EEG by Means of the Bispectrum

The bispectrum of a stationary stochastic process, which contains a wave component that is not sine-shaped, describes the amplitude and phase relations between the harmonic components of that wave. The bispectrum of EEG signal gives information about an averaged wave shape of a dominant component of the signal, i. e., whether it contains phase-locked higher order terms, and the amplitude and phase relations between the components can be estimated if the phase-locked relation exists. Normal subjects were recorded while lying down with eyes closed. The monopolar recordings with α-activity from@ electrodes on left and right occipital regions were analyzed by means of the bispectrum. For the recordings that were obtained within 30 minutes and had typical α-activity, the modulus and phase of the bispectrum remain almost constant in spite of individual differences. The bispectra of the recordings from corresponding left and right sides showed the same value for the recordings that were regarded to have symmetry. Asymmetry of left and right sides of the bispectra was observed in the data during the attack of migraine. These findings are statistically examined and discussed