Long hour polygraphic recordings were repeatedly performed in 19 premature, 8 small for date and 3 full term infants. The recordings were made every week or two after delivery until the time of their calculated date of aerm gestation. No difference is presen t electroencephalographically among REM sleep, wakefulness and non-REM sleep before 32 weeks of conceptional age. EEG is characterized by burst-suppression pattern.1320c/s spindle like fast rhythm with 0.5-1.5 slow waves are characteristically seen in bursts. Difference between REM and non-REM sleep appears for the first time around 3 2-33 weeks. The latter is characterized by burst-suppression pattern (an immature pattern of trace alternant). After 34-35 weeks, REM sleep shows low voltage desynchronized pattern with some semirhythmic theta and alpha waves which increase with advancing age. Difference between moderately deep sleep and deep sleep appears for the first time around 36-37weeks. The former is characterized by increase of slow waves and their amplitudes (slow wave sleep pattern). The latter shows trace alternapt.13-20c/s spindle like fast rhythm decreases gradually to disappear around 40 weeks. After 36-37 weeks EEG shows gradual development with increase of activity in each stage. Burst-burst intervals of trace alternant decrease gradually with advancing age but their modal values are relatively constant throughout various conceptional ages.
