Developmental characteristics of normal and mentally retarded children's EEGs

Abstract

It was necessary to reexamine the findings that the frequency of the EEG in children increases gradually with age. Using the method of spectrum analysis of EEG in normal and mentally retarded children, the authors examined the developmental characteristics of the frequency components both cross-sectionally and longitudinally. The EEG was taken monopolarly from 4 places along the midline (F, C, P, O) and the temporal places of the both hemispheres (LT, RT). Auto-power spectra of the EEG from the frontal, central and occipital regions were obtained by a minicomputer. Analysis time was 10 sec and frequency resolution was 1 3 c/sec . From 50 spectra an averaged auto-power spectrum was obtained. From the cross-sectional study, the following was obtained: 1. (1) In the normal group, the frequency of the dominant components changed with age until about 10 c/sec. However, the time course of the change was different among regions. The dominant component of about 10 c/sec appeared in all 3 regions at about 10 years. In the mentally retarded group, dominant components of about 10 c/sec were hardly observed and frequencies of the dominant and subordinate components varied widely among individuals and age groups. 2. (2) In both normal and mentally retarded groups, the alpha component appeared first in the occipital region as a subordinate component and subsequently became dominant. After the generation of the alpha component in the occipital region, it also appeared in the central and frontal regions, and became dominant in that order. 3. (3) In many cases in both normal and retarded groups, multiple peaks were observed when a dominant component in the spectrum appeared at frequency lower than 7 c/sec, subordinate ones were found at frequencies higher than 8 c/sec; conversely if a dominant component was generated at a frequency higher than 8 c/sec, subordinate ones were at lower frequencies. From the longitudinal study, the following results were obtained. 4. (4) In both normal and mentally retarded groups, earlier dominant components at the lower frequency later became the subordinate one without changing frequency or eventually disappeared. Moreover, a previously subordinate component or a new one at a higher frequency grew into a new dominant component. 5. (5) EEGs generated in the process of maturation are composed of different components at discrete frequencies that differ from each other in origin. The frequency of the dominant component is heightened not continuously but stepwise with increasing age. 6. (6) It may be accepted that the relative dominancy among the components reflects in part the maturational progress or retardation of the brain and that the processes of developmental change of the brain functioning in the retarded children are essentially identical to that of the normal, except for some pathological cases.