Table 1.

Developmental changes of amount, polysomnographic, behavioral, and physiological characteristics, and timing in the sleep-wake cycle of REM sleep across early development of humans.

Parameters		REM Sleep	References
Amount	Preterm	80% of TST at 30 GW, 67% between 33 and 35 GW, 58% between 36 and 38 GW.	[13,31,32]
	Full-term	50% of TST in full-term newborns.	[9,10,11,12,38]
	Postnatal	Progressive reduction with age, reaching 20% of TST at about three years of age and remaining constant throughout childhood, adolescence, and adulthood.	[9,11,12,39,40]
EEG	Preterm	Inconstant EEG of REM sleep is surveyed <30 GW, a constant pattern is observed during 36–38 GW. EEG remains atypical.	[13,31,34,37,42]
	Full-term	Easy identification with low-voltage, relatively fast activities, frequent occurrence of REM sleep directly succeeds waking episodes at sleep onset.	[12,35,43,44]
	Postnatal	EEG patterns progressively increase in frequency and amplitude. The occurrence of sleep beginning with REM sleep declines with age, from 60% at 3 weeks to 20% at 6 months.	[49]
Rapid eye movements (REMS)	Preterm	Eye movements are very rare <28 GW. number of REMS remains lower.	[35,54]
	Full-term	More REMS, EOG invariably appears as single or clustered high-amplitude bursting waves.	[43,44]
	Postnatal	REMS starts to increase after birth, reaching a plateau at about 4 months.	[55]
Spontaneous body movements	Preterm	A large number between 38 and 40 GW, but the amount is lesser than that in full-term newborns.	[53]
	Full-term	Atonia becomes obvious. Grimaces, small weak cries, smiles, and twitches of the face and extremities are frequently observed. EMG shows phasic muscular contractions in the background of the absence of resting muscle activity.	[12,13]
	Postnatal	Spontaneous smiles generally diminish and disappear at 2–3 months and are replaced by social smiles. Spontaneous body movements decline with age.	[62,64]
Breathing	Preterm	Irregular, frequent apnea, periodic breathing <38 GW.	[13,66]
	Full-term	The respiratory rate during REM sleep is 18% greater than that during NREM sleep. Frequent apnea.	[12]
	Postnatal	For infants from 1 month to >9 months of age, the mean respiratory rate during REM sleep decreases from 35.8 to 22.3 breath/min	[68]
Heart rate	Preterm	Irregular, 130 beats/min at 37 GW.	[13,35]
	Full-term	115–120 beats/min, the mean heart rate is 3.4% higher during REM sleep than during NREM sleep.	[12,67]
	Postnatal	For infants from 1 month to >9 months of age, REM sleep decreases from 134.7 to 110.8 beats/min	[68]
Sleep-wake cycle	Preterm	Approximately 60 min.	[34,69]
	Full-term	The mean duration of sleep cycles and mean length of REM sleep in newborns are respectively 52.9 and 25.4 min. The amount of REM sleep in the 1st cycle is approximately 1/2 of that in subsequent individual cycles. The mean duration of REM sleep prolongs almost threefold in the 2nd cycle and tends to diminish slightly in the 3rd cycle.	[12]
	Postnatal	Length of sleep cycles across the first year of age is progressively increasing with age. REM sleep periods become longer towards the morning hours. After the age of 10, the sleep cycle lasts about 90–110 min as in an adult.	[12,39,76]