Quantitative analysis of infant EEG development during quiet sleep

Abstract

A quantitative evaluation of central cortical EEG activity during quiet sleep was undertaken in normal infants followed from 1 to 24 weeks of age. Bilateral (C 3-T 3, C 4-T 4) EEG activity was recorded continuously on magnetic tape during 12-h polygraphic monitoring sessions at 1, 4, 8, 12, 16 and 24 weeks of age. Power-spectral densities were calculated from three independent 10 min quiet sleep samples from the first, middle and last epochs of the night. Data were calibrated, log transformed and sorted into five sequential 4 c/sec frequency bands between 0–19 c/sec. Analysis focused upon the distribution of power in these bands as a function of time of night, hemisphere and age. A time of night effect was found only between 8 and 16 weeks of age. During this period the initial sleep epoch showed a significant increase in low frequency power. This was interpreted as an age-specific sleep deprivation effect related to experimental manipulation of the infant. No significant developmental difference in power distribution was found between hemispheres, although specific asymmetries were noted. All frequency bands changed significantly with age. Lower frequencies (0–3 and 4–7 c/sec) increased in power with age, 0–3 c/sec increasing abruptly from 1 to 8 weeks and 4–7 c/sec showing a more delayed increment after 12 weeks of age. Power in the higher frequency bands (8–11, 12–15 and 16–19 c/sec decreased between 1 and 4 weeks and then increased significantly at 12 weeks and older. The decrease at 4 weeks and increase at 12 weeks was most marked for the 12–15 c/sec band, and was interpreted in terms of the development of thalamocortical mechanisms related to the generation of EEG sleep spindles.