second type of development, experience-dependent brain development, refers to the growth that occurs in response to learning experiences (Bick & Nelson, 2017). For example, experiences such as learning to stack blocks or crawl on a slippery wood floor are unique to individual infants, and they influence what particular brain areas and functions are developed and reinforced. Experience-dependent development is the result of lifelong experiences that vary by individual based on contextual and cultural circumstances (Kolb, 2018; Kolb et al., 2014). Exposure to enriching experiences, such as interactive play with toy cars and other objects that move; hands-on play with blocks, balls, and cups; and stimulating face-to-face play can all enhance children’s development (Kolb, 2018). For example, a longitudinal study that followed more than 350 infants from 5 to 24 months of age found that the quality of mother–infant interactions at 5 months predicted greater brain activity in the prefrontal cortex at 10 and 24 months of age, suggesting that parenting quality may contribute to brain development in infancy (Bernier, Calkins, & Bell, 2016). On the other hand, exposure to deprivation and trauma can have lasting negative effects on brain development (Harker, 2018).
Sleep and Brain Development
Whereas adults sleep approximately 8 hours each day, the typical neonate sleeps about 16 to 18 hours each day. Sleep declines steadily. Six-month-old infants sleep about 12 hours (Figueiredo, Dias, Pinto, & Field, 2016). Infant rats, rabbits, cats, and rhesus monkeys also sleep much longer than adults, suggesting that sleep serves a developmental function (Blumberg, Gall, & Todd, 2014). Sleep promotes physical growth and development (Tham, Schneider, & Broekman, 2017). In adults, sleep is thought to permit the body to repair itself, as indicated by increased cell production and the removal of metabolic wastes during sleep (Tononi & Cirelli, 2014). Sleep is also associated with increases in connections among neurons (Krueger, Frank, Wisor, & Roy, 2016).
One hypothesis for infants’ increased time in sleep is that it provides stimulation and promotes brain development.
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In adults, sleep is associated with memory consolidation, “cementing” memories, and sleep deficits are associated deficits in attention, memory, and learning (Chambers, 2017; Doyon, Gabitov, Vahdat, Lungu, & Boutin, 2018; Spencer, Walker, & Stickgold, 2017). Rapid eye movement (REM) sleep, during which adults’ eyes flutter and dreaming occurs, is particularly important for cognitive functioning (Lewis, 2017). Infants spend about half of their sleep time in REM sleep, decreasing to about 20% in adulthood. REM sleep is thought to provide infants with stimulation and promote brain development and cognitive growth (Friedrich, Wilhelm, Mölle, Born, & Friederici, 2017; Tham et al., 2017). Neonates with poor sleep patterns showed poor attention at 4 months and increased distractibility at 18 months of age (Geva, Yaron, & Kuint, 2016). Similar to findings with adults, one study found that sleep was associated with memory formation in 3- to 8-month-old infants (Friedrich et al., 2017). Sleep may have long-term effects on cognitive development. An examination of infants at 12 months of age and again at 3 to 4 years old showed that lower-quality sleep in infancy was associated with problems with attention and behavioral control in early childhood (Sadeh et al., 2015).
Sleeping serves a developmental function, yet young infants wake often (Mäkelä et al., 2018). The typical newborn wakes every 2 hours to eat, and babies continue to require nighttime feedings until they are 4 or 5 months old. Many continue to wake at night. Cultures differ in infant sleep practices. For example, parents in the United States typically look forward to the time when their infant will sleep through the night, viewing the newborn’s unpredictable sleep pattern as something to fix. In contrast, many European parents view newborn sleep as part of normal development and do not intervene to shape newborn sleep cycles. Children in Pacific-Asian countries tend to sleep an hour less than those in North America, Europe, and Australia (Galland, Taylor, Elder, & Herbison, 2012; Mindell, Sadeh, Wiegand, How, & Goh, 2010). Parental behavior influences infants’ sleep patterns. Infants are more likely to continue waking overnight when their parents play with them during nighttime feedings, as stimulation and attention may reinforce nighttime waking (Sadeh et al., 2015). Cultures also have different practices around sleeping arrangements for infants, toddlers, and older children—including co-sleeping and bedsharing (see the Lives in Context feature).
Lives in Context: Cultural Context
Co-sleeping
The practice of co-sleeping, which refers to the infant sharing a bed with the mother or with both parents, is common in many countries yet controversial in others. In Japan, China, Kenya, Bangladesh, and the Mayan peninsula of Mexico, co-sleeping in infancy and early childhood is the norm and is believed to enhance the child’s sense of security and attachment to the mother (Huang, Wang, Zhang, & Liu, 2010; Morelli, Rogoff, Oppenheim, & Goldsmith, 1992; Super & Harkness, 1982). In Latin America and Asia, infants are not usually expected to go to bed and sleep alone at a regular time each night. Instead, they are held until they fall asleep and then are placed in the parental bed (Lozoff, Wolf, & Davis, 1984). In contrast, in many industrialized countries, such as the United States and the United Kingdom, newborns are placed to sleep in their own bassinets, whether in their parents’ room or in a separate nursery. In these countries, learning to sleep by oneself is viewed as fostering independence and the ability to self-regulate (Ball, Hooker, & Kelly, 1999; McKenna & Volpe, 2007). Parents’ decisions of whether to co-sleep are influenced by their own values and beliefs, which are often shaped by the context in which they live.
While sharing a bedroom can enhance the infant–parent bond and make nighttime feedings easier, infants are safest in their own bassinets, such this one, which is adapted to promote safe parent–infant contact.
Jennie Hart / Alamy Stock Photo
Proponents of co-sleeping argue that it best meets the developmental needs of human newborns and aids in forming the attachment bond (McKenna, 2001). Infants who sleep with their mothers synchronize their sleep patterns with hers, permitting more awakenings for breastfeeding, yet lengthening the total time that infants sleep (Gettler & McKenna, 2011). Both mothers and babies benefit from skin-to-skin contact, as it enhances breast milk production, stabilizes infants’ heart rate, increases the prevalence and duration of breastfeeding, and is associated with more positive mother–infant interactions (McKenna & Volpe, 2007; Taylor, Donovan, & Leavitt, 2008). Fathers report that they find co-sleeping rewarding rather than an intrusion on the marital bed (Ball, Hooker, & Kelly, 2000).
Pediatricians in Western nations tend to advise separate sleeping arrangements for parents and infants. Opponents of co-sleeping point to an increased risk of accidental suffocation and an increased risk of SIDS (sudden infant death syndrome), especially among mothers who smoke (Mitchell, 2009). The American Academy of Pediatrics and the U.K. Department of Health have declared sharing a bed with an infant to be an unsafe practice; instead, they advise having infants sleep in a crib in the parents’ room (Task Force on Sudden Infant Death Syndrome, 2016; U.K. Department of Health, 2005). Despite these warnings, co-sleeping has become more common among Western families. Some believe that co-sleeping can be safe if appropriate precautions are taken, such as using light bed coverings and a firm mattress and avoiding comforters and pillows (McKenna, 2001). The American Academy of Pediatrics advises that bedsharing should be abandoned in favor of room sharing, to provide the developmental advantages of co-sleeping and minimize the dangers (Task Force on Sudden Infant Death Syndrome, 2016).
What Do You Think?
1 In your view, what are the advantages and disadvantages of co-sleeping?
2 In what ways might parent–child sleeping