Spectral analysis of the abnormal theta rhythm in the EEG of young children.

The abnormal theta rhythm of the EEG of early childhood was investigated by spectral analysis. The pattern in the power spectrum is characterized by a peak in the thetaband. The relative peak intensity (peak ratio = ratio of peak intensity and average intensity of the spectrum within the frequency range of 0--10 Hz) as well as the right-left coherence proved to be good criteria for the description of the abnormal theta rhythms. When the ratio q greater than or equal to 2.0 and the coherence Coh greater than or equal to 0.7 an abnormal theta rhythm can be considered to be present. When this definition is applied, a high correspondence between the mathematical and visual evaluation of the EEG is present. The abnormal theta rhythm must be regarded as a symptom of a functional anomaly which is -- under electroencephalographic aspects -- characterized by generators acting in abnormal synchronism and monofrequency.