Decomposition of posterior alpha rhythm.

The classical posterior alpha rhythm has been decomposed into regular and irregular components using orthogonal transformation. A periodicity generator is considered, which has three characteristic control parameters: the periodicity, the amplitudes or scaling factors and the pattern associated with successive periodic segments. The regular component is shown to be equivalent to an oscillator or periodicity generator whose parameters are dynamically varying and, thus, producing both amplitude- and frequency-modulation. The irregular component is devoid of such modulating behavior. Electroencephalogram signals from normal, maniac and epileptic subjects are studied. Through analytic signal-based analysis, it is shown that for the regular component, healthy brain possesses universal scaling behavior, whereas heterogeneous scaling or absence of universality is observed for the diseased brain.