Experimental studies of infant-parent co-sleeping: mutual physiological and behavioral influences and their relevance to SIDS (sudden infant death syndrome)

doi:10.1016/0378-3782(94)90211-9

Early Human Development

Volume 38, Issue 3, 15 September 1994, Pages 187-201

https://doi.org/10.1016/0378-3782(94)90211-9 Get rights and content

Abstract

We hypothesize that maternal sensory exchanges, likely involving a combination of heat, sound, gas, smells, movement, and touch, induce important physiological changes, especially in the healthy infant's arousal patterns, body temperature, and sleep architecture as defined by standard physiological measures. We summarize the results of two preliminary physiological studies, and some early data from a third, in which mothers and infants are monitored using standard polysomnographic techniques as they sleep in the same bed, and then in adjacent rooms. Our data suggest that infant-parent co-sleeping alters the infant's sleep experience as, for example, the characteristics of arousals, the frequency and duration of nursing, infant sleep position and the number of maternal inspections. For example, while sleeping in the same bed, mothers nurse their infants three times more frequently than they do while their infants sleep in an adjacent room. These preliminary data demonstrate significant differences between routine co-sleeping and solitary sleeping environments. This work underscores the importance of studying infant sleep as it unfolds in the co-sleeping environment, the environment within which it evolved over at least 5 million years of human evolution. Should our preliminary findings be confirmed in future studies they will provide a beginning point for considering additional, possibly unconventional ways of helping to reduce SIDS risks.

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Human infants spend most of their time sleeping, but over the first few years of life their sleep becomes regulated to coincide more closely with adult sleep (Galland et al., 2012; Paavonen et al., 2020). Evidence shows that co-sleeping played a role in the evolution of infant sleep regulation, as it is part of an ancient behavioral complex representing the biopsychosocial microenvironment in which human infants co-evolved with their mothers through millions of years of human history (Ball, 2003; McKenna 1986, 1990). This paper is a conceptual, interdisciplinary, integration of the literature on mother-infant co-sleeping and other mother-infant co-regulatory processes from an evolutionary (biological) perspective, using complexity science. Viewing the mother-infant dyad as a “complex adaptive system” (CAS) shows how the CAS fits assumptions of regulatory processes and reveals the role of the CAS in the ontogeny of mother-infant co-regulation of physiological (thermoregulation, breathing, circadian rhythm coordination, nighttime synchrony, and heart rate variability) and socioemotional (attachment and cortisol activity) development.
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A risk factor for SIDS is sleeping in a separate room and the AAP (2016) recommends parent-infant roomsharing (without bedsharing) to reduce risk. The ability to closely monitor an infant is therefore important; bedsharing mothers check on, inspect, touch, and breastfeed their infants significantly more than mothers of solitary-sleeping infants (McKenna et al., 1994). No matter infant sleep location, lack of parental monitoring is a significant risk for SIDS/SUID (AAP, 2016).
Bedsharing is controversial for nighttime caregiving in the U.S. today, as in most of the West. However, from the standpoint of evolutionary pediatrics, anthropology, and cultural psychology, bedsharing is not controversial at all, representing the context for human infant evolution and conferring a host of physiological benefits to the infant as well as the mother. In an effort to understand the rise in Western bedsharing in recent decades (and following Ball, 2002; McKenna & Volpe, 2007), Salm Ward (2015) systematically reviewed the literature on mother-infant bedsharing and identified ten reasons why mothers choose to bedshare: (1) breastfeeding, (2) comforting for mother or infant, (3) better/more sleep for infant or parent, (4) monitoring, (5) bonding/ attachment, (6) environmental reasons, (7) crying, (8) cultural or familial traditions, (9) disagree with danger, and (10) maternal instinct. The current paper offers the “review behind the review,” highlighting the scientific evidence behind the reasons mothers give for their decision to bedshare, focusing on how mothers’ decisions about infant sleep location influence infant behavior and development.
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Citation Excerpt :
Along the same line of thought, infants who regularly co-sleep were expected to have developed greater physiological self-regulation and adapt better to changes in sleeping condition compared to their counterparts who regularly sleep beyond arm’s length and sleep solitarily owing to enhanced mutual regulation when dyadic partners are in close physical contact (Ball et al., 2000; Chu, 2014; Keller & Goldberg, 2004, 2004b, McKenna & Mosko, 1994; McKenna & McDade, 2005). Alternatively, it was also hypothesized that physiological self-regulatory responses of calming may be evident in infants who are regular solitary sleepers as predicted by an opposing notion that regular solitary sleeping promotes self-regulation in infants (Burnham et al., 2002; Keller & Goldberg, 2004; McKenna & Mosko, 1994; McKenna et al., 1994). Our results indicated that infants who regularly co-slept with their mothers had the longest IBIs across all three sleeping arrangement conditions, followed by infants who regularly slept beyond arm’s length from their mothers.
This study aimed to understand how different mother-infant sleeping arrangements impact infants’ self-regulation, particularly their calming response. Thus this study investigated the effect of three prevalent mother-infant sleeping arrangements, co-sleeping (CS), sleeping beyond arm’s length from their mother (BAL), and solitary sleeping (SS), on infants’ physiological calming through self-regulation during a nap session in 24 infants (50% female, M = 1.85 months SD = 0.93 months), who were identified as either regular co-sleepers with their mothers, infants who slept in the BAL sleeping arrangement from their mother, and infants who are solitary sleepers (SS). The effect of all three sleeping conditions amongst all the three types of infants with different habitual sleeping arrangements was assessed. All infants spent 10 min (2 × 5 min sessions) in each sleeping condition (CS, BAL, SS) during which electrocardiographic recordings were collected to obtain interbeat intervals (IBI) and rMSSD, a measure of heart rate variability (HRV) an index of physiological calming, maintained by the parasympathetic pathway involved in self-regulation. Infants who regularly co-slept with their mothers had the highest IBI, indicating greater physiological calming and self-regulation across all sleeping arrangement conditions (CS, BAL, SS), followed by infants who regularly slept in the BAL sleeping arrangement from their mothers. IBI was lowest amongst regular solitary sleepers, potentially indicating physiological stress due to mother-infant separation. However, HRV indices during the sleeping arrangements (especially across regular solitary sleepers) were inconclusive as to whether the lack of change in HRV across all sleeping conditions was due to physiological stress responses or greater physiological regulation. This study is the first to investigate the effect of manipulated and habitual mother-infant sleeping arrangements on infant physiological calming.
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The practice of parent and child sharing a sleeping surface, or ‘bed-sharing’, is one of the most controversial topics in parenting research. The lay literature has popularized and polarized this debate, offering on one hand claims of dangers, and on the other, of benefits – both physical and psychological – associated with bed-sharing. To address the scientific evidence behind such claims, we systematically reviewed 659 published papers (peer-reviewed, editorial pieces, and commentaries) on the topic of parent-child bed-sharing. Our review offers a narrative walkthrough of the many subdomains of bed-sharing research, including its many correlates (e.g., socioeconomic and cultural factors) and purported risks or outcomes (e.g., sudden infant death syndrome, sleep problems). We found general design limitations and a lack of convincing evidence in the literature, which preclude making strong generalizations. A heat-map based on 98 eligible studies aids the reader to visualize world-wide prevalence in bed-sharing and highlights the need for further research in societies where bed-sharing is the norm. We urge for multiple subfields – anthropology, psychology/psychiatry, and pediatrics – to come together with the aim of understanding infant sleep and how nightly proximity to the parents influences children's social, emotional, and physical development.
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Findings from experimental research indicate that even brief separations from a caregiver elicit exaggerated physiologic responses in children with SAD (based on a range of cardiac, respiratory, and electrodermal measures) and, on reunion with the caregiver, sympathetic arousal is slower to return to baseline levels in comparison with both controls and children with other anxiety disorders.57 In animal models, there is evidence for alterations in REM sleep among rat and monkey infants following separation from mothers,58 highlighting the possible role of architectural sleep changes as a contributor to longer-term difficulties with sleep and regulation of emotion. Inasmuch as physiologic hyperarousal and sleep initiation and maintenance are inherently incompatible processes,59 it is unsurprising that these children exhibit bedtime resistance, difficulties with falling asleep, and prolonged nighttime awakenings.

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Arousal mechanisms and infant careExperimental studies of infant-parent co-sleeping: mutual physiological and behavioral influences and their relevance to SIDS (sudden infant death syndrome)

Abstract

The Nature of the Child

Infant-parent co-sleeping in evolutionary perspective: implications for understanding infant sleep development and SIDS

Sleep

An anthropological perspective on the sudden infant death syndrome (SIDS): the role of parental breathing cues and speech breathing adaptations

Med. Anthropol.

Evolution of human behavior development

Nursing frequency, gonadal function and birth spacing among Kung humter-gatherers

Science

Dr. Spock's Baby and Child Care

Sudden infant death scene investigation

N. Engl. J. Med.

Bed sharing, smoking and alcohol in the sudden infant death syndrome

Br. Med. J.

The ecology of weaning: parasitism and the achievement of independence by altricial mammals

Parental contributions to the development of offspring

Rethinking healthy infant sleep

La Leache League Abstr.

Sleep and arousal patterns of co-sleeping human mother-infant pairs: a preliminary physiological study with implications for the study of sudden infant death syndrome (SIDS)

Am. J. Phys. Anthropol.

Arousal mechanisms and infant care
Experimental studies of infant-parent co-sleeping: mutual physiological and behavioral influences and their relevance to SIDS (sudden infant death syndrome)