63 polygraphic recordings were performed in 14 premature infants at 3-6 days after birth and every two weeks thereafter longitudinally, until their expected date of delivery. At 40 conceptional weeks, four different EEG patterns, i. e., trace alternant, moderately deep sleep. REM and drowsy REM patterns, were distinguished. Clinically two sleep stages, quiet and active sleeps, were observed in all recordings.
Trace alternant and moderately deep sleep constitute the quiet sleep while REM and drowsy REM the active sleep. Quiet and active sleeps form the one sleep cycle which has the duration of about 90 minutes and is constant from 32 conceptional weeks through 40 weeks. The duration of four EEG patterns in one sleep cycle were quantitatively analysed every week. Percentage of REM and drowsy REM (active sleep) among the whole sleep cycle shows no change during maturation, that is about 60%. At 36 conceptional weeks drowsy REM was distinguished in active sleep from real REM with low amplitude fast wave EEG and this occupies about 10% in one sleep cycle. That means, real REM stage decreases from 36 conceptional weeks and finally constitutes 45.6% at 40 conceptional weeks. Absolute duration of trace alternant also decreases with conceptional weeks, namely 27.7 minutes at 32 conceptional weeks to 14.8 minutes at 40 weeks. Percentage of moderately deep sleep which is obscure before 35 weeks and perhaps same as slow wave sleep in adults, increases from 10.8% of quiet sleep at 35 weeks to 42. 2% at 40 weeks.
