Abstract: Electroencephalographic investigations of the spontaneous and "evoked" potentials were performed on 758 normal preschool children with an Ediswan 16-channel electroencephalograph. "Evoked" potentials was initiated by "threshold" single and repetitive flashes of light:1. EEG aged 4—7 years show an outstanding competition between α and θ waves. At about 7 years of age this competition is finished on 51.5% children in the occipital region, but only on 6.7% children in the temporal region.2. From 4—7 years the occipital rhythmic activity increases in frequency but amplitude stands high with age. The range of changes in frequency always exceeds 1±1/sec.3. The vast majority of children aged 4—7 years shows the phenomenon of "dicrotic" and "muhicrotic".4. Short duration and low percentage of display are the traits of the "blocking" responses elicited by "threshold" single flashes on preschool children.5. Occasional display, narrow range of "driving" frequency and absence of afterdischarge are the traits of the "driving" responses elicited by "threshold" repetitive flashes on preschool children.6. Our results show that it seems to have a period of acceleration of brain's development between 5—6 years of age.

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