Neonates active sleep

Infants are able to acquire odor preferences on the first day of life. In one experiment, 12 male and 12 female white, healthy, full-term neonates were exposed to the odors of cherry or ginger on a pad taped to the inside of their crib for 24 hours. After this exposure, they were tested for preferences during active sleep (stage II). The behavior was videotaped and the duration of time oriented to each odor measured. Only the female neonates showed a preference for the familiar odor (Balogh and Porter, 1986). Therefore, even on the first day of life, females outperform males, as often described for children and adults (e.g. Yousem etal, 1999). 

Phasic muscle twitches are one of the major REM phasic activities in neonates and also comprise prominent neonatal behavior. A similar feature is found not only in rats but also in other rodents and humans. The period that shows frequent muscle twitches is the first 4 weeks in the rat (4), the first 40 days in the kitten (8), and the first 8 months in the human newborn (13). In humans, this feature is more typical in the premature fetus (14). This activity appears primarily during REM sleep but also in a small portion of NREM sleep, i.e., half-activated sleep (4). The rate of muscle twitches is only 1.5/min and 0.3/min during quiet sleep compared to the rate of 7.5/min and 3/min, respectively, during REM sleep at the same age in PN 10 and PN 20 kittens (8). The number of phasic events dramatically decreases as animals mature (8,9,13,15). It is of interest to note that the dramatic reduction of phasic activities in REM sleep is associated with the increase of wakefulness. 

Vogel GW, Feng P. A reply to Frank and Heller about neonatal active sleep. Sleep 2000 23 1005-1011. 

Hilakivi (ref. 128) found that in rats prenatal alcohol exposure during the entire period of pregnancy resulted in less active sleep, more wake and a more frequent interruption of the quiet sleep state by waking episodes on neonatal age. Human newborns with FAS may show abnormal EEG profiles and sleep disturbances such as reduced REM sleep (ref. 25). 

In adult humans and animals, chronic intermittent hypoxia has a facilatory effect manifest by enhanced responses to acute hypoxia (52,53), which appears to involve a serotonin-dependent mechanism (53). Both facilatory and inhibitory effects have been observed in neonatal animals (48,50,51). In addition, state of arousal has been shown to be a factor in the response to repetitive hypoxia in the neonate. In newborn lambs, for example, repetitive hypoxia rapidly became ineffective as a stimulus during active sleep but retained its responses during quiet sleep (49). 

Both the words neonatal and postnatal (PN) have been used in the study of early-life phenomena in rats. Neonatal refers to a period from birth to 2 weeks in the clinic. The developmental level of the newborn rat is equal to the third trimester of the human fetus and the 2-week old rat is equal to the human newborn (6). Landmarks in the rat are the eye opening and the end of so-called stress hyporesponsive period (SHRP) at this age (7). Thus, it is reasonable to call a rat neonatal at the age of 2 weeks or younger. There are more landmarks during the developmental period. One is that sleep-wake distribution nears adult level and the other is the appearance of sexual activity. Ages at these landmarks in the rat are approximately 1 month for the former and 2 months for the latter (4). Thus, it is important to consider the timing of neonatal rapid-eye-movement... 

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