Topographical distribution of delta rhythms during sleep: evolution with age

This study concerns the evolution of slow EEG activities (delta rhythms) and their topographical distribution during 31 night sleep records of 27 control subjects whose ages ranged from 1 month to 27 years. A system of data processing allows the representation of continuous changes in 8 derivations of the power of 0.5--4.5 c/sec waves. The obtained curves, whose respective magnitudes depend on the chosen montage, parallel the sleep cycles of the classical hypnogram. They do not clearly differentiate NREM sleep stages, but show a progressive increase of delta rhythm power with the deepening of NREM sleep. Moreover, measurement of the magnitude to these curves allows comparisons between the different channels in a given record and between different recordings. With the referential setting used in this study the topographical organization of the occipital, parietal and central curves proved occipital, parietal and central curves proved remarkably consistent in all subjects. The general magnitude of these curves decreased with age while that of frontal curves slightly increased. The right parietal curves were of greater magnitude than the left in every record obtained from children aged 2--5 years. The changes with age, and the intra- and interindividual differences are discussed. The data suggest hypotheses about the importance of NREM sleep in developmental processes.