TRENDS IN ELECTROENCEPHALOGRAPHIC SYNCHRONIZATION ACROSS NONRAPID EYE-MOVEMENT SLEEP IN INFANTS

The trend of synchronized (high-voltage, low-frequency) electroencepha lographic (EEG) activity was determined across nonrapid eye movement ( NREM) sleep periods of night sleep in two groups of infants (eight ''y oung infants'', age 2-19 weeks; eight ''older infants'', age 21-54 wee ks) and, as a reference, in a group of eight adults (age 16-45 years). By automatic analysis of the sleep EEG, a parameter was derived that represents the degree of synchronized (high-amplitude, low-frequency) EEG activity for successive 30-second epochs. For each subject, the av erage level of EEG synchronization for each NREM period and the time o f the NREM period midpoints were determined. In all three groups, sync hronized EEG activity tended to decrease across successive NREM period s. This trend was weaker for infants than for adults and, surprisingly , weaker for older than for young infants. This suggests that the decr easing trend typical for adults is already present in the first months after birth. The difference in trend between infants and adults may b e caused by differences in the 24-hour sleep-wakefulness distribution, whereas the distinction between young and older infants could be rela ted to a restructuring of sleep in the second semester, in particular to the emergence of slow-wave sleep and its peculiar distribution acro ss NREM periods of night sleep.