Post-natal Slow Wave Sleep Inhibition and the SIDS "Back to Sleep" Campaign

In human infants sleep develops rapidly during early development. This development includes an increase in non-rapid eye movement (NREM) sleep which is also called Quiet Sleep (QS) during the first 12 months of life in association with a decrease in rapid eye movement (REM) sleep which is also known as Active Sleep (AS) [1-3]. In addition, slow wave sleep (SWS) which consists of Stage 3 and Stage 4 NREM sleep appears at 2 months of age [4-7].

In a currently utilized model that explains the process in which slow wave sleep is involved in memory consolidation the hippocampus acts as a temporary storage facility for new memories which are then transferred to the neocortex during slow wave sleep (SWS) [8]. In this model, acetylcholine acts a feedback loop inhibitor inside the hippocampus during REM sleep and wakefulness. The activity during the high cholinergic wakefulness period is believed to provide an environment which allows for the encoding within the hippocampus of new declarative memories. The low cholinergic environment during SWS is thought to then allow these memories to be transferred from the temporary storage of the hippocampus to their permanent storage environment in the neocortex and for memory consolidation [9, 10].

A significant way of decreasing slow wave sleep in infants is by changing their sleeping position from prone to supine. It has been shown in studies of preterm infants [11, 12], full-term infants [13, 14], and older infants [15], that they have greater time periods of quiet sleep and also decreased time awake when they are positioned to sleep in the prone position. In both human infants and rats, arousal thresholds have been shown to be at higher levels in the EEG delta range [16-18]. In addition, Epidemiological studies strongly associate the prone sleep position to a higher risk of SIDS for infants [19-21]. Based upon the epidemiological evidence and studies of sleep physiology, the American Academy of Pediatrics developed a supine sleep position SIDS risk reduction strategy which is based on decreasing arousal thresholds and decreasing quiet sleep for infants [22].

In 1992 [23], a SIDS risk reduction strategy based upon lowering arousal thresholds during SWS was implemented by the American Academy of Pediatrics (AAP) which began recommending that healthy infants be positioned to sleep on their back (supine position) or side (lateral position), instead of their stomach (prone position), when being placed down for sleep. The AAP’s 1992 recommendations were announced five years after the Netherlands had started it’s infant supine sleep position campaign in 1987 [24]. The Netherlands recommendations were followed by infant supine sleep position campaigns in the United Kingdom, New Zealand, and Australia in 1991, the U.S. and Sweden in 1992, and Canada in 1993 [25, 26]. In 1994 [27], a number of organizations in the United States combined to further communicate these non-prone sleep position recommendations and this became formally known as the “Back To Sleep” campaign. In 1996 [28], the AAP further refined its sleep position recommendation by stating that infants should only be placed to sleep in the supine position and not in the prone or lateral positions.

In 1992, the first National Infant Sleep Position (NISP) Household Survey [29] was conducted to determine the usual position in which U.S. mothers placed their babies to sleep. According to the 1992 NISP survey, 13.0% of U.S. infants were positioned in the supine position for sleep [30]. According to the 2006 NISP survey 75.7% of infants were positioned in the supine position to sleep [31]. Mothers that are younger and those that are less well-educated are more likely to put their infants to sleep in the prone position [32-34].

Since 1998 there have been three studies published which show that infants placed to sleep in the supine position lag in motor skills, social skills, and cognitive ability development when compared to infants who sleep in the prone position [35-37]. None of these three studies analyzed children older than 18 months of age and the authors of all three studies considered the lags at less than 18 months of age to be temporary and do not think that the supine sleep recommendations should be changed. Placing infants in the prone position while they are awake has been recommended to offset the motor skills delays associated with the supine sleep position [38] but positioning the infant prone while awake will not impact the amount of slow wave sleep [39-43].

SIDS deaths in the U.S. decreased from 4,895 in 1992 to 2,247 in 2004 [44]. But, during a similar time period, 1989 to 2004, SIDS being listed as the cause of death for sudden infant death (SID) decreased from 80% to 55% [45]. In addition, maternal pregnancy smoking rates decreased by 38% during a similar time period, 1990-2002 [46]. According to Dr. John Kattwinkel, chairman of the Center for Disease Control (CDC) Special Task Force on SIDS "A lot of us are concerned that the rate (of SIDS) isn't decreasing significantly, but that a lot of it is just code shifting” [47]. Considering that the original non-prone sleep recommendations were implemented 16 years ago in the U.S. and that human development is not always linear it may be time to re-evaluate the long-term impact of the “Back to Sleep” Campaign on motor skills, social skills, and cognitive ability.

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