Correlating EEG and IQ: A new look at an old problem using computerized EEG parameters

Explorations of the relationship between EEG activity and scores of tests of intelligence have a long history. Results have been rather discrepant and several explanations can be offered for this. Almost all previous studies relied on parameters derived from a visual rather than a computerized analysis of the EEG. Here broad band spectral parameters were mainly used, and in addition the frequency of the dominant peak (at P_z, O₁ and O₂) between 6.5 and 14.0 Hz. All EEG parameters were standardized for age, as were tests of intelligence. Correlations of EEG with IQ were computed separately for a group of normal and a group of mildly retarded children. As postulated in advance, correlations were substantially higher for the retarded groups. Even more remarkable than the size of the correlations found was their pattern, associated with an interesting interpretation: the sign of the larger correlations was such that children developmentally more advanced in their EEG parameters had on the average higher IQ scores. Moreover, correlations were large for those frequency bands, and to a lesser degree for those derivations where we found a high developmental relevance in a previous investigation for the age range considered. Some disappointing or even discrepant results in earlier studies can be explained in the light of the results given here.