Longitudinal developmental course of electrical activity of brain.

Different phases of brain growth precede maturation as indicated in the developmental course of brain electrical activity. This can be illustrated by EEG and evoked potentials recorded from the scalp from a postmenstrual age of 24 weeks. A description of electrical patterns according to postmenstrual age is valid because of the strong relationship between electrical activity and brain maturation, regardless of "gestational" age at birth and birthweight. For evaluation of the electrical activity of the brain especially in preterm infants and during the first year of life sleep studies have been invaluable. In the first year of life the EEG is characterized by appearance and disappearance of special patterns and by an increasing synchronization between hemispheres. Later during childhood and adolescence especially before and in the course of puberty there is an intense maturation which is seen in the EEG by the appearance of rhythmic and paroxysmal patterns related to age and sex. The slowly increasing frequency of the background occipital rhythm and the response to photic stimulation with increasing frequency of photic driving are sensitive indicators of brain maturation. In adolescence there are fewer differences in regard to age and sex dependence which may be an expression for a tapering off of the maturation process. This is in accordance with the general concept of the terminal ordinary growth in man. Developmental changes of evoked responses are also in accordance with the morphological maturation. Measurement of evoked potentials is especially useful in newborns where cerebral maturation can be studied and evaluated.