Sticky mittens study found that

section three

Babies are such a nice way to start people.

—Don Herold

American Writer, 20th Century

Infancy
As newborns, we were not empty-headed organisms. We had some basic reflexes, among them crying, kicking, and coughing. We slept a lot, and occasionally we smiled, although the meaning of our first smiles was not entirely clear. We ate and we grew. We crawled and then we walked, a journey of a thousand miles beginning with a single step. Sometimes we conformed; sometimes others conformed to us. Our development was a continuous creation of more complex forms. We needed the meeting eyes of love. We juggled the necessity of curbing our will with becoming what we could will freely. This section contains three chapters: “Physical Development in Infancy,” “Cognitive Development in Infancy,” and “Socioemotional Development in Infancy.”

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chapter 4
PHYSICAL DEVELOPMENT IN INFANCY
chapter outline
1 Physical Growth and Development in Infancy

Learning Goal 1 Discuss physical growth and development in infancy.

Patterns of Growth

Height and Weight

The Brain

Sleep

Nutrition

2 Motor Development

Learning Goal 2 Describe infants’ motor development.

The Dynamic Systems View

Reflexes

Gross Motor Skills

Fine Motor Skills

3 Sensory and Perceptual Development

Learning Goal 3 Summarize the course of sensory and perceptual development in infancy.

What Are Sensation and Perception?

The Ecological View

Visual Perception

Other Senses

Intermodal Perception

Nature, Nurture, and Perceptual Development

Perceptual-Motor Coupling

image1 ©Image Source/Getty Images

Latonya is a newborn baby inPage 105 Ghana. During her first days of life, she has been kept apart from her mother and bottle fed. Manufacturers of infant formula provide the hospital where she was born with free or subsidized milk powder. Her mother has been persuaded to bottle feed rather than breast feed her. When her mother bottle feeds Latonya, she overdilutes the milk formula with unclean water. Latonya’s feeding bottles have not been sterilized. Latonya becomes very sick. She dies before her first birthday.

Ramona was born in a Nigerian hospital with a “baby-friendly” program. In this program, babies are not separated from their mothers when they are born, and the mothers are encouraged to breast feed them. The mothers are told of the perils that bottle feeding can bring because of unsafe water and unsterilized bottles. They also are informed about the advantages of breast milk, which include its nutritious and hygienic qualities, its ability to immunize babies against common illnesses, and the role of breast feeding in reducing the mother’s risk of breast and ovarian cancer. Ramona’s mother is breast feeding her. At 1 year of age, Ramona is very healthy.

image2 (Top) An HIV-infected mother breast feeding her baby in Nairobi, Kenya. (Bottom) A Rwandan mother bottle feeding her baby. What are some concerns about breast versus bottle feeding in impoverished African countries?(Top) ©Wendy Stone/Corbis/Getty Images; (bottom) ©Dave Bartruff/Corbis/Getty Images

For many years, maternity units in hospitals favored bottle feeding and did not give mothers adequate information about the benefits of breast feeding. In recent years, the World Health Organization and UNICEF have tried to reverse the trend toward bottle feeding of infants in many impoverished countries. They instituted “baby-friendly” programs in many countries (Grant, 1993). They also persuaded the International Association of Infant Formula Manufacturers to stop marketing their baby formulas to hospitals in countries where the governments support the baby-friendly initiatives (Grant, 1993). For the hospitals themselves, costs actually were reduced as infant formula, feeding bottles, and separate nurseries became unnecessary. For example, baby-friendly Jose Fabella Memorial Hospital in the Philippines reported saving 8 percent of its annual budget. Still, there are many places in the world where the baby-friendly initiatives have not been implemented.

The advantages of breast feeding in impoverished countries are substantial (UNICEF, 2017). However, these advantages must be balanced against the risk of passing the human immunodeficiency virus (HIV) to babies through breast milk if the mothers have the virusPage 106 (Croffut & others, 2018; Mnyani & others, 2017; Wojcicki, 2017). In some areas of Africa, more than 30 percent of mothers have HIV, but the majority of these mothers don’t know that they are infected (Mepham, Bland, and Newell, 2011). Later in the chapter, in the section on nutrition, we will look more closely at recent research on breast feeding in the United States, outlining the benefits for infants and mothers and discussing several life-threatening diseases that infants can contract as a result of malnutrition.

topical connections looking back
Previously, we followed the physical development that takes place from fertilization through the germinal, embryonic, and fetal periods of prenatal development. We learned that by the time the fetus has reached full gestational age (approximately 40 weeks), it has grown from a fertilized egg, barely visible to the human eye, to a fully formed human weighing approximately 8 pounds and measuring 20 inches in length. Also remarkable is the fact that by the end of the prenatal period the brain has developed approximately 100 billion neurons.

preview

It is very important for infants to get a healthy start. When they do, their first two years of life are likely to be a time of amazing development. In this chapter, we focus on the biological domain and the infant’s physical development, exploring physical growth, motor development, and sensory and perceptual development.

1 Physical Growth and Development in Infancy
LG1 Discuss physical growth and development in infancy.

Patterns of Growth

Height and Weight

The Brain

Sleep

Nutrition

Infants’ physical development in the first two years of life is extensive. Newborns’ heads are quite large in comparison with the rest of their bodies. They have little strength in their necks and cannot hold their heads up, but they have some basic reflexes. In the span of 12 months, infants become capable of sitting anywhere, standing, stooping, climbing, and usually walking. During the second year, growth decelerates, but rapid increases in such activities as running and climbing take place. Let’s now examine in greater detail the sequence of physical development in infancy.

A baby is the most complicated object made by unskilled labor.
—Anonymous

PATTERNS OF GROWTH
An extraordinary proportion of the total body is occupied by the head during prenatal development and early infancy (see Figure 1 ). The cephalocaudal pattern is the sequence in which the earliest growth always occurs at the top—the head—with physical growth and differentiation of features gradually working their way down from top to bottom (for example, shoulders, middle trunk, and so on). This same pattern occurs in the head area,Page 107because the top parts of the head—the eyes and brain—grow faster than the lower parts, such as the jaw.

image3 FIGURE 1 CHANGES IN PROPORTIONS OF THE HUMAN BODY DURING GROWTH. As individuals develop from infancy through adulthood, one of the most noticeable physical changes is that the head becomes smaller in relation to the rest of the body. The fractions listed refer to head size as a proportion of total body length at different ages.

Motor development generally proceeds according to the cephalocaudal principle. For example, infants see objects before they can control their torso, and they can use their hands long before they can crawl or walk. However, development does not follow a rigid blueprint. One study found that infants reached for toys with their feet prior to reaching with their hands (Galloway & Thelen, 2004). On average, infants first touched the toy with their feet when they were 12 weeks old and with their hands when they were 16 weeks old.

Growth also follows the proximodistal pattern , the sequence in which growth starts at the center of the body and moves toward the extremities. For example, infants control the muscles of their trunk and arms before they control their hands and fingers, and they use their whole hands before they can control several fingers (Bindler & others, 2017).

HEIGHT AND WEIGHT
The average North American newborn is 20 inches long and weighs 7.6 pounds. Ninety-five percent of full-term newborns are 18 to 22 inches long and weigh between 5 and 10 pounds.

In the first several days of life, most newborns lose 5 to 7 percent of their body weight before they adjust to feeding by sucking, swallowing, and digesting. Then they grow rapidly, gaining an average of 5 to 6 ounces per week during the first month. They have doubled their birth weight by the age of 4 months and have nearly tripled it by their first birthday. Infants grow about 1 inch per month during the first year, approximately doubling their birth length by their first birthday.

Growth slows considerably in the second year of life (London & others, 2017). By 2 years of age, infants weigh approximately 26 to 32 pounds, having gained a quarter to half a pound per month during the second year to reach about one-fifth of their adult weight. At 2 years of age, infants average 32 to 35 inches in height, which is nearly half of their adult height.

An important point about growth is that it often is not smooth and continuous but rather is episodic, occurring in spurts (Adolph, 2018; Adolph & Berger, 2015). In infancy, growth spurts may occur in a single day and alternate with long time frames characterized by little or no growth for days and weeks (Lampl & Johnson, 2011; Lampl & Schoen, 2018). In two analyses, in a single day, infants grew seven-tenths of an inch in length in a single day (Lampl, 1993) and their head circumference increased three-tenths of an inch (Caino & others, 2010).

THE BRAIN
We have described the amazing growth of the brain from conception to birth. By the time it is born, the infant that began as a single cell is estimated to have a brain that contains approximately 100 billion nerve cells, or neurons. Extensive brain development continues after birth, through infancy and later (Sullivan & Wilson, 2018; Vasa & others, 2018). Because the brain is still developing so rapidly in infancy, the infant’s head should be protected from falls or other injuries and the baby should never be shaken. Shaken baby syndrome, which includes brain swelling and hemorrhaging, affects hundreds of babies in the United States each year (Hellgren & others, 2017). One analysis found that fathers were the most frequent perpetrators of shaken baby syndrome, followed by child care providers and boyfriends of the victim’s mother (National Center on Shaken Baby Syndrome, 2012).

Researchers have been successful in using the electroencephalogram (EEG), a measure of the brain’s electrical activity, to learn about the brain’s development in infancy (Bell & others, 2018; Hari & Puce, 2017) (see Figure 2 ). For example, a recent study found that higher-quality mother-infant interaction early in infancy predicted higher-quality frontal lobe functioning that was assessed with EEG later in infancy (Bernier, Calkins, & Bell, 2016).

image4 FIGURE 2 MEASURING THE ACTIVITY OF AN INFANT’S BRAIN WITH AN ELECTROENCEPHALOGRAM (EEG). By attaching up to 128 electrodes to a baby’s scalp to measure the brain’s activity, researchers have found that newborns produce distinctive brain waves that reveal they can distinguish their mother’s voice from another woman’s, even while they are asleep. Why is it so difficult to measure infants’ brain activity?Courtesy of Vanessa Vogel Farley

Researchers also are increasingly using functional near-infrared spectroscopy (fNIRS), which uses very low levels of near-infrared light to monitor changes in blood oxygen, to study infants’ brain activity (de Oliveira & others, 2018; Emberson & others, 2017a, b; Taga, Watanabe, & Homae, 2018) (see Figure 3 ). Unlike fMRI, which uses magnetic fields or electrical activity, fNIRS is portable and allows the infants to be assessed as they explore the world around them. And recently Patricia Kuhl and her colleagues (Ferjan Ramirez & others, 2017) at the Institute for Learning and Brain Sciences at the University of Washington have been using magnetoencephalography,Page 108 or MEG, brain-imaging machines to assess infants’ brain activity. MEG maps brain activity by recording magnetic fields produced by electrical currents and is being used to assess such perceptual and cognitive activities as vision, hearing, and language in infants (see Figure 4 ).

image5 FIGURE 3 FUNCTIONAL NEAR-INFRARED SPECTROSCOPY (fNRIS) Functional near-infrared spectroscopy is increasingly being used to examine the brain activity of infants. fNRIS is non-invasive and can assess infants as they move and explore their environment.©Oli Scarff/Getty Imagesimage6 FIGURE 4 MEASURING THE ACTIVITY OF AN INFANT’S BRAIN WITH MAGNETOENCEPHALOGRAPHY (MEG). This baby’s brain activity is being assessed with a MEG brain-imaging device while the baby is listening to spoken words in a study at the Institute of Learning and Brain Sciences at the University of Washington. The infant sits under the machine and when he or she experiences a word, touch, sight, or emotion, the neurons working together in the infant’s brain generate magnetic fields and MEG pinpoints the location of the fields in the brain.©Dr. Patricia Kuhl, Institute for Learning and Brain Sciences, University of Washington

Among the researchers who are making strides in finding out more about the brain’s development in infancy are:

· Charles Nelson and his colleagues (Berens & Nelson, 2015; Bick & Nelson, 2018; Bick & others, 2017; Finch & others, 2017; McLaughlin, Sheridan, & Nelson, 2017; Nelson, 2007, 2012, 2013a, b; Nelson, Fox, & Zeanah, 2014; Vanderwert & others, 2016; Varcin & others, 2016) who are exploring various aspects of memory development, face recognition and facial emotion, and the role of experience in influencing the course of brain development;

· Martha Ann Bell and her colleagues (Bell, 2015; Bell & Cuevas, 2012, 2014, 2015; Bell & others, 2018; Bell, Ross, & Patton, 2018; Broomell & Bell, 2018; Li & others, 2017; MacNeill & others, 2018; Lusby & others, 2016) who are studying brain-behavior links, emotion regulation, inhibitory control, and the integration of cognition and emotion;

· Mark Johnson and his colleagues (Anzures & others, 2016; Gliga & others, 2017; Hakuno & others, 2018; Johnson, Jones, & Gliga, 2015; Johnson, Senju, & Tomalski, 2015; Milosavlijevic & others, 2017; Saez de Urabain & others, 2017; Senju & others, 2016), who are examining neuroconstructivist links between the brain, cognitive and perceptual processes, and environmental influences as well as studying the development of the prefrontal cortex and its functions, early identification of autism, face processing, and early social experiences; and

· John Richards and his colleagues (Emberson & others, 2071a; Lloyd-Fox & others, 2015; Richards, 2009, 2010, 2013; Richards & others, 2015; Richards, Reynolds, & Courage, 2010; Richards & Xie, 2015; Xie, Mallin, & Richards, 2018; Xie & Richards, 2016, 2017) who are examining sustained attention, perception of TV programs, and eye movements.

developmental connection
Brain Development
How does the brain change from conception to birth? Connect to “Prenatal Development and Birth.”

The Brain’s Development At birth, the newborn’s brain is about 25 percent of its adult weight. By the second birthday, the brain is about 75 percent of its adult weight. However, the brain’s areas do not mature uniformly.

Mapping the Brain Scientists analyze and categorize areas of the brain in numerous ways (Bell & others, 2018; Dean & others, 2018; Ferjan Ramirez & others, 2017). The portion farthest from the spinal cord is known as the forebrain. This region includes the cerebral cortex and several structures beneath it. The cerebral cortex covers the forebrain like a wrinkled cap. The brain has two halves, or hemispheres (see Figure 5 ). Based on ridges and valleys in the cortex, scientists distinguish four main areas, called lobes, in each hemisphere. Although the lobes usually work together, each has a somewhat different primary function (see Figure 6 ):

image7 FIGURE 5 THE HUMAN BRAIN’S HEMISPHERES. The two hemispheres of the human brain are clearly seen in this photograph. It is a myth that the left hemisphere is the exclusive location of language and logical thinking and that the right hemisphere is the exclusive location of emotion and creative thinking.©A.Glauberman/Science Sourceimage8 FIGURE 6 THE BRAIN’S FOUR LOBES. Shown here are the locations of the brain’s four lobes: frontal, occipital, temporal, and parietal.

· Frontal lobes are involved in voluntary movement, thinking, personality, and intentionality or purpose.

· Occipital lobes function in vision.

· Temporal lobes have an active role in hearing, language processing, and memory.

· Parietal lobes play important roles in registering spatial location, attention, and motor control.

To some extent, the type of information handled by neuronsPage 109 depends on whether they are in the left or right hemisphere of the cortex (Benjamin & others, 2017; Sidtis & others, 2018). Speech and grammar, for example, depend on activity in the left hemisphere in most people; humor and the use of metaphors depend on activity in the right hemisphere (Holler-Wallscheid & others, 2017). This specialization of function in one hemisphere of the cerebral cortex or the other is called lateralization . However, most neuroscientists agree that complex functions such as reading or performing music involve both hemispheres. Labeling people as “left-brained” because they are logical thinkers or “right-brained” because they are creative thinkers does not correspond to the way the brain’s hemispheres work. Complex thinking in normal people is the outcome of communication between both hemispheres of the brain (Nora & others, 2017; Raemaekers & others, 2018).

At birth, the hemispheres of the cerebral cortex already have started to specialize: Newborns show greater electrical brain activity in the left hemisphere than the right hemisphere when they are listening to speech sounds (Telkemeyer & others, 2011). How are the areas of the brain different in the newborn and the infant from those in an adult, and why do the differences matter? Important differences have been documented at both the cellular and the structural levels.

Changes in Neurons Within the brain, the type of nerve cells called neurons send electrical and chemical signals, communicating with each other. A neuron is a nerve cell that handles information processing (see Figure 7 ). Extending from the neuron’s cell body are two types of fibers known as axons and dendrites. Generally, the axon carries signals away from the cell body and dendrites carry signals toward it. A myelin sheath, which is a layer of fat cells, encases many axons (see Figure 7 ). The myelin sheath insulates axons and helps electrical signals travel faster down the axon (Cercignani & others, 2017; van Tilborg & others, 2018). Myelination also is involved in providing energy to neurons and in communication (Saab & Nave, 2017). At the end of the axon are terminal buttons, which release chemicals called neurotransmitters into synapses, which are tiny gaps between neurons’ fibers. Chemical interactions in synapses connect axons and dendrites, allowing information to pass from neuron to neuron (Ismail, Fatemi, & Johnson, 2017; Zhou & others, 2018). Think of the synapse as a river that blocks a road. A grocery truck arrives at one bank of the river, crosses by ferry, and continues its journey to market. Similarly, a message in the brain is “ferried” across the synapse by a neurotransmitter, which pours out information contained in chemicals when it reaches the other side of the river.

image9 FIGURE 7 THE NEURON. (a) The dendrites of the cell body receive information from other neurons, muscles, or glands through the axon. (b) Axons transmit information away from the cell body. (c) A myelin sheath covers most axons and speeds information transmission. (d) As the axon ends, it branches out into terminal buttons.

Neurons change in two very significant ways during the first years of life. First, myelination, the process of encasing axons with fat cells, begins prenatally and continues after birth, even into adolescence and emerging adulthood (Juraska & Willing, 2017). Second, connectivity among neurons increases, creating new neural pathways (Eggebrecht & others, 2017; Zhou & others, 2018). New dendrites grow, connections among dendrites increase, and synaptic connections between axons and dendrites proliferate. Whereas myelination speeds up neural transmissions, the expansion of dendritic connections facilitates the spreading of neural pathways in infant development.

How complex are these neural connections? In a recent analysis, it was estimated that each of the billions of neurons is connected to as many as 1,000 other neurons, producing neural networks with trillions of connections (de Haan, 2015). As we have discussed previously, most of these billions of neurons essentially have been created, have traveled to their correct locations, and are connected to other neurons by the time of full-term birth. Nonetheless, they undergo further differentiation, and neural connectivity patterns continue to change at least into emerging adulthood (Vasa & others, 2018).

Researchers have discovered an intriguing aspect of synaptic connections: nearly twice as many of these connections are made as will ever be used (Huttenlocher & Dabholkar, 1997). The connections that are used survive and become stronger, while the unused ones are replaced by other pathways or disappear. In the language of neuroscience, these connections will be “pruned” (Gould, 2017). For example, the more babies engage in physical activity or use language, the more those pathways will be strengthened.

developmental connection
Brain Development
Changes in the prefrontal cortex in adolescents and older adults have important implications for their cognitive development. Connect to “Physical and Cognitive Development in Adolescence” and “Physical Development in Late Adulthood.”

The age at which “blooming” and subsequent “pruning” of synapses occurs varies by brain region. For example, the peak of synaptic overproduction in the visual cortex occurs at about the fourth postnatal month, followed by a gradual retraction until the middle to end of the preschool years. In areas of the brain involved in hearing and language, a similar, though somewhat later, course is detected. However, in the prefrontal cortex, the area of the brain where higher-level thinking and self-regulation occur, the peak of overproduction takes place at about 1 year of age; it is not until emerging adulthood that adult density of synapses is attained. Both heredity and environment are thought to influence the timing and course of synaptic overproduction and subsequent retraction.

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Early Experience and the Brain Children who grow up in a deprived environment may have depressed brain activity (Bick & Nelson, 2018; Bick & others, 2017; McLaughlin, Sheridan, & Nelson, 2017; Nelson, Fox, & Zeanah, 2014). As shown in Figure 8 , a child who grew up in the unresponsive and unstimulating environment of a Romanian orphanage showed considerably depressed brain activity compared with a child who grew up in a normal environment.

image10 FIGURE 8 EARLY DEPRIVATION AND BRAIN ACTIVITY. These two photographs are PET (positron emission tomography) scans, which use radioactive tracers to image and analyze blood flow and metabolic activity in the body’s organs. These scans show the brains of (a) a typically developing child and (b) an institutionalized Romanian orphan who experienced substantial deprivation since birth. In PET scans, the highest to lowest brain activity is reflected in the colors of red, yellow, green, blue, and black, respectively. As can be seen, red and yellow show up to a much greater degree in the PET scan of the typically developing child than the deprived Romanian orphan.Courtesy of Dr. Harry T. Chugani, Children’s Hospital of Michigan

Are the effects of deprived environments reversible? There is reason to think that for some individuals the answer is “yes” (Dennis & others, 2014). The brain demonstrates both flexibility and resilience. Consider 14-year-old Michael Rehbein. At age 7, he began to experience uncontrollable seizures—as many as 400 a day. Doctors said the only solution was to remove the left hemisphere of his brain where the seizures were occurring. Recovery was slow, but his right hemisphere began to reorganize and take over functions that normally occur in the brain’s left hemisphere, including speech (see Figure 9 ).

image11 FIGURE 9 PLASTICITY IN THE BRAIN’S HEMISPHERES. (a) Michael Rehbein at 14 years of age. (b) Michael’s right hemisphere (right) has reorganized to take over the language functions normally carried out by corresponding areas in the left hemisphere of an intact brain (left). However, the right hemisphere is not as efficient as the left, and more areas of the brain are recruited to process speech.Courtesy of The Rehbein Family

Neuroscientists believe that what wires the brain—or rewires it, in the case of Michael Rehbein—is repeated experience. Each time a baby tries to touch an attractive object or gazes intently at a face, tiny bursts of electricity shoot through the brain, knitting together neurons into circuits. The results are some of the behavioral milestones we discuss in this chapter.

The Neuroconstructivist View Not long ago, scientists thought that our genes determined how our brains were “wired” and that the cells in the brain responsible for processing information just maturationally unfolded with little or no input from environmental experiences. Whatever brain your heredity had dealt you, you were essentially stuck with. This view, however, turned out to be wrong. Research reveals that the brain has plasticity and its development depends on context (Bick & Nelson, 2018; D’Souza & Karmiloff-Smith, 2018; McLaughlin & Broihier, 2018; Snyder & Smith, 2018).

The infant’s brain depends on experiences to determine how connections are made. Before birth, it appears that genes mainly direct basic wiring patterns. Neurons grow and travel to distant places awaiting further instructions. After birth, the inflowing stream of sights, sounds, smells, touches, language, and eye contact help shape the brain’s neural connections.

In the increasingly popular neuroconstructivist view , (a) biological processes (genes, for example) and environmental conditions (enriched or impoverished, for example) influence the brain’s development; (b) the brain has plasticity and is context dependent; and (c) the child’s cognitive development is closely linked to development of the brain. These factors constrain or advance the construction of cognitive skills (Goldberg, 2017; Mucke & others, 2018; Schreuders & others, 2018; Westermann, Thomas, & Karmiloff-Smith, 2011). The neuroconstructivist view emphasizes the importance of considering interactions between experience and gene expression in the brain’s development, much as the epigenetic view proposes (Moore, 2017; Smith & others, 2018; Westermann, 2016).

developmental connection
Nature and Nurture
In the epigenetic view, development is an ongoing, bidirectional interchange between heredity and the environment. Connect to “Biological Beginnings.”

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SLEEP
Sleep restores, replenishes, and rebuilds our brains and bodies. What function does sleep have in people’s lives? How do sleep patterns change in infancy?

Why Do We Sleep? A number of theories have been proposed about why we sleep. From an evolutionary perspective, all animals sleep and this sleep likely is necessary for survival. Thus, sleep may have developed because animals needed to protect themselves at night. A second perspective is that sleep replenishes and rebuilds the brain and body, which the day’s waking activities can wear out. In support of this restorative function, many of the body’s cells show increased production and reduced breakdowns of proteins during sleep (Frank, 2017). Further, a current emphasis is that sleep is essential to clearing out waste in neural tissues, such as metabolites and cerebrospinal fluid (Aguirre, 2016). A third perspective is that sleep is critical for brain plasticity (Sterpenich, Ceravolo, & Schwartz, 2017). For example, neuroscientists recently have argued that sleep increases synaptic connections between neurons (Areal, Warby, & Mongrain, 2017). These increased synaptic connections during sleep have been linked to improved consolidation of memories (Gui & others, 2017). Further, a research review concluded that not only can sleep improve memory, but losing a few hours of sleep a night is related to negative effects on attention, reasoning, and decision making (Diekelmann, 2014).

In sum, sleep likely serves a number of functions with no one theory accounting for all of the functions. Let’s now turn our attention to sleep in infancy. In later chapters, we will explore sleep through the remainder of the life span.

Sleep that knits up the ravelled sleave of care . . . Balm of hurt minds, nature’s second course. Chief nourisher in life’s feast.
—William Shakespeare

English Playwright, 17th Century

Infant Sleep When we were infants, sleep consumed more of our time than it does now (Goh & others, 2017). The typical newborn sleeps approximately 18 hours a day, but newborns vary greatly in how much they sleep (Dias & others, 2018; Sadeh, 2008). The range is from about 10 hours to about 21 hours a day.

In a recent study, sleep sessions lasted approximately 3.5 hours during the first few months and increased to about 10.5 hours from 3 to 7 months (Mindell & others, 2016). A previous research review concluded that infants 0 to 2 years of age slept an average of 12.8 hours out of the 24, within a range of 9.7 to 15.9 hours (Galland & others, 2012). Another study revealed that by 6 months of age the majority of infants slept through the night, awakening their parents only once or twice a week (Weinraub & others, 2012).

Sleep problems have been estimated to affect 15 to 25 percent of infants. The most common infant sleep-related problem reported by parents is nighttime waking (Dias & others, 2018; Hospital for Sick ChildrenPage 112 & others, 2010). Surveys indicate that 20 to 30 percent of infants have difficulty going to sleep at night and staying asleep until morning (Sadeh, 2008). One study found that nighttime wakings at 1 year of age predicted lower sleep efficiency at 4 years of age (Tikotzky & Shaashua, 2012). Further research found that (1) maternal depression during pregnancy, (2) early introduction of solid foods, (3) infant TV viewing, and (4) child care attendance were related to shorter duration of infant sleep (Nevarez & others, 2010). And a recent study revealed that later bedtime and less sleep across a 24-hour period were linked to infants having more separation distress, greater inhibition, and higher anxiety and depression levels (Mindell & others, 2017).

Research also indicates that parental factors other than maternal depression are linked to infants’ sleep patterns (Field, 2017; Volkovich & others, 2018; Yu & others, 2017). A recent study found that maternal sleep when the infant was 3 months of age predicted the infant’s sleep patterns at 6 months of age and that increased involvement of the father in caregiving responsibilities improved the infant’s sleep (Tikotzky & others, 2015). And other recent research indicated that a higher level of maternal emotional availability at bedtime was associated with a lower level of infant distress at bedtime and longer infant sleep duration (Philbrook & Teti, 2016).

Cultural variations influence infant sleeping patterns (Field, 2017). For example, in the Kipsigis culture in Kenya, infants sleep with their mothers at night and are permitted to nurse on demand (Super & Harkness, 1997). During the day, they are strapped to their mothers’ backs, accompanying them on daily rounds of chores and social activities. As a result, the Kipsigis infants do not sleep through the night until much later than American infants do. During the first eight months of postnatal life, Kipsigis infants rarely sleep longer than three hours at a stretch, even at night. This sleep pattern contrasts with that of American infants, many of whom begin to sleep up to eight hours a night by 8 months of age.

REM Sleep In REM sleep, the eyes flutter beneath closed lids; in non-REM sleep, this type of eye movement does not occur and sleep is more quiet (Bathory & Tomopoulos, 2017). Figure 10 shows developmental changes in the average number of total hours spent in REM and non-REM sleep. By the time they reach adulthood, individuals spend about one-fifth of their night in REM sleep, and REM sleep usually appears about one hour after non-REM sleep. However, about half of an infant’s sleep is REM sleep, and infants often begin their sleep cycle with REM sleep rather than non-REM sleep. A much greater amount of time is taken up by REM sleep in infancy than at any other point in the life span. By the time infants reach 3 months of age, the percentage of time they spend in REM sleep falls to about 40 percent, and REM sleep no longer begins their sleep cycle.

image12 FIGURE 10 DEVELOPMENTAL CHANGES IN REM AND NON-REM SLEEP

Why do infants spend so much time in REM sleep? Researchers are not certain. The large amount of REM sleep may provide infants with added self-stimulation, since they spend less time awake than do older children. REM sleep also might promote the brain’s development in infancy (Graven, 2006).

When adults are awakened during REM sleep, they frequently report that they have been dreaming, but when they are awakened during non-REM sleep, they are much less likely to report having been dreaming (Cartwright & others, 2006). Since infants spend more time than adults in REM sleep, can we conclude that they dream a lot? We don’t know whether infants dream or not, because they don’t have any way of reporting dreams.

Shared Sleeping Sleeping arrangements for newborns vary from culture to culture (Field, 2017). For example, sharing a bed with a mother is a common practice in many cultures, such as Guatemala and China, whereas in others, such as the United States and Great Britain, newborns usually sleep in a crib, either in the same room as the parents or in a separate room. In some cultures, infants sleep with the mother until they are weaned, after which they sleep with siblings until middle and late childhood (Walker, 2006). Whatever the sleeping arrangements, it is recommended that the infant’s bedding provide firm support and that the crib has side rails (Kreth & others, 2018).

In the United States, shared sleeping remains a controversial issue (Burnham, 2014). Some experts recommend it and others argue against it, although recently the recommendation trend has been to avoid infant-parent bed sharing, especially if the infant is younger than 6 months of age (Byard, 2012a, b; Field, 2017; Mitchell & others, 2017; Weber & others, 2012). In a recent study, infant-parent bed sharing was associated with more night waking for mothers as wellPage 113 as infants, and more marital distress (Teti & others, 2016). The American Academy of Pediatrics Task Force on Infant Positioning and SIDS (AAPTFIPS) (2000) recommends against shared sleeping. Its members argue that in some instances bed sharing might lead to sudden infant death syndrome (SIDS), as could be the case if a sleeping mother rolls over on her baby (Moon & others, 2017). Recent studies have found that bed sharing is linked with a higher incidence of SIDS, especially when parents smoke (Adams, Ward, & Garcia, 2015). Further, a recent large-scale study in six countries (including the United States) found that parents of 6- to 12-month-old infants reported earlier bedtimes, shorter time to fall asleep, fewer sleep interruptions, and more total sleep when the infants slept in a separate room compared with infants sleeping in the same room or same bed with their parents (Mindell, Leichman, & Walters, 2018).

SIDS Sudden infant death syndrome (SIDS) is a condition that occurs when infants stop breathing, usually during the night, and die suddenly without any apparent reason. SIDS continues to be a leading cause of infant death in the United States, with more than 2,000 infant deaths annually attributed to SIDS (NICHD, 2018). Risk of SIDS is highest at 2 to 4 months of age.

developmental connection
Sleep
What are some sleep problems that children encounter in early childhood? Connect to “Physical and Cognitive Development in Early Childhood.”

Since 1992, the American Academy of Pediatrics (AAP) has recommended that infants be placed to sleep on their backs (supine position) to reduce the risk of SIDS, and the frequency of prone sleeping (on the stomach) among U.S. infants has dropped dramatically (AAPTFIPS, 2000). Researchers have found that SIDS does indeed decrease when infants sleep on their backs rather than their stomachs or sides (Bombard & others, 2018; Siren, 2017; Sperhake, Jorch, & Bajanowski, 2018). Why? Because sleeping on their backs increases their access to fresh air and reduces their chances of getting overheated.

developmental connection
Sleep
Sleep patterns change in adolescence and are linked to changes in the brain. Connect to “Physical and Cognitive Development in Adolescence.”

In addition to sleeping in a prone position, researchers have found that the following factors are linked to SIDS:

· SIDS occurs more often in infants with abnormal brain stem functioning involving the neurotransmitter serotonin (Rognum & others, 2014; Rubens & Sarnat, 2013).

· Heart arrhythmias are estimated to occur in as many as 15 percent of SIDS cases, and two studies found that gene mutations were linked to the occurrence of these arrhythmias (Brion & others, 2012; Van Norstrand & others, 2012).

· Six percent of infants with sleep apnea, a temporary cessation of breathing in which the airway is completely blocked, usually for 10 seconds or longer, die of SIDS (Ednick & others, 2010).

· Breast feeding is linked to a lower incidence of SIDS (Carlin & Moon, 2017).

· Low birth weight infants are 5 to 10 times more likely to die of SIDS than are their normal-weight counterparts (Horne & others, 2002).

· SIDS is more likely to occur in infants who do not use a pacifier when they go to sleep than in those who do use a pacifier (Carlin & Moon, 2017). A recent research review confirmed that pacifier use is linked to a lower incidence of SIDS (Alm & others, 2016).

· Infants whose siblings have died of SIDS are two to four times as likely to die of it (Lenoir, Mallet, & Calenda, 2000).

· African American and Eskimo infants are four to six times as likely as all others to die of SIDS (Kitsantas & Gaffney, 2010; Moon & others, 2017).

· SIDS is more common in lower socioeconomic groups (Hogan, 2014).

· SIDS is more common in infants who are passively exposed to cigarette smoke (Horne, 2018; Salm Ward & Balfour, 2016).

· SIDS is more common when infants and parents share the same bed (Carlin & Moon, 2017; Moon & others, 2017). A recent Swedish study confirmed that bed sharing was more common in SIDS cases than in other types of infant deaths (Mollborg & others, 2015).

· SIDS is more common if infants sleep in soft bedding (McGarvey & others, 2006).

· SIDS is less common when infants sleep in a bedroom with a fan. One study revealed that sleeping in a bedroom with a fan lowers the risk of SIDS by 70 percent (Coleman-Phox, Odouli, & Li, 2008).

image13 Is this a good sleep position for infants? Why or why not?©Maria Teijeiro/Getty Images

It is generally accepted that the most critical factor in predicting whether an infant will develop SIDS is prone sleeping. As public awareness has grown regarding the importance of not letting infants sleep in a prone position, the number of infant deaths in the United States has decreased, although SIDS still is one of the leading causes of infant deathPage 114 (Bombard & others, 2018). In a recent research review, it was concluded that the two other factors that place infants at the highest risk for SIDS are (1) maternal smoking and (2) bed sharing (Mitchell & Krous, 2015).

One concern raised by critics of the “back to sleep movement” (ensuring that young infants sleep on their back rather than their stomach) is a decline in prone skills. To prevent this decline, many mothers provide their young infants with “tummy time” by periodically placing them on their stomachs when they are awake.

Sleep and Cognitive Development Might infant sleep be linked to children’s cognitive development? A recent research review indicated that there is a positive link between infant sleep and cognitive functioning, including memory, language, and executive function (Tham, Schneider, & Broekman, 2017). A study also revealed that a lower quality of sleep at 1 year of age was linked to lower attention regulation and more behavior problems at 3 to 4 years of age (Sadeh & others, 2015). And in another study, infants with poorer sleep patterns showed more distractibility during an attention task (Geva, Yaron, & Kuint, 2016). The link between infant sleep and children’s cognitive functioning likely occurs because of sleep’s role in brain maturation and memory consolidation, which may improve daytime alertness and learning.

NUTRITION
From birth to 1 year of age, human infants nearly triple their weight and increase their length by 50 percent. What do they need to sustain this growth?

Nutritional Needs and Eating Behavior Individual differences among infants in terms of their nutrient reserves, body composition, growth rates, and activity patterns make defining actual nutrient needs difficult (Borowitz & Borowitz, 2018; Rolfes & Pinna, 2018). However, because parents need guidelines, nutritionists recommend that infants consume approximately 50 calories per day for each pound they weigh—more than twice an adult’s caloric requirement per pound.

A number of developmental changes involving eating characterize the infant’s first year (Leow & others, 2017). As infants’ motor skills improve, they change from using suck-and-swallow movements with breast milk or formula to chew-and-swallow movements with semisolid and then more complex foods. As their fine motor control improves in the first year, they transition from being fed by others toward self-feeding. “By the end of the first year of life, children can sit independently, can chew and swallow a range of textures, are learning to feed themselves, and are making the transition to the family diet and meal patterns” (Black & Hurley, 2007, p. 1). At this point, infants need to have a diet that includes a variety of foods—especially fruits and vegetables.

Caregivers play very important roles in infants’ early development of eating patterns (Baye, Tariku, & Mouquet-Rivier, 2018; Brown, 2017). Caregivers who are not sensitive to developmental changes in infants’ nutritional needs, caregivers who are negligent, and conditions of poverty can contribute to the development of eating problems in infants (Black & Hurley, 2017; Perez-Escamilla & Moran, 2017). One study found that low maternal sensitivity when infants were 15 and 24 months of age was linked to a higher risk of obesity in adolescence (Anderson & others, 2012). And in a recent study, infants who were introduced to vegetables at 4 to 5 months of age showed less fussy eating behavior at 4 years of age than their counterparts who were introduced to vegetables after 6 months (de Barse & others, 2017).

A national study of more than 3,000 randomly selected 4- to 24-month-olds documented that many U.S. parents were feeding their babies too much junk food and not giving them enough fruits and vegetables (Fox & others, 2004). Up to one-third of the babies ate no vegetables and fruit but frequently ate French fries, and almost half of the 7- to 8-month-old babies were fed desserts, sweets, or sweetened drinks. By 15 months, French fries were the most common vegetable the babies ate.

Such poor dietary patterns early in development can result in more infants being overweight (Black & Hurley, 2017; Blake, 2017; Feldman-Winter & others, 2018). In addition to consuming too many French fries, sweetened drinks, and desserts, are there other factors that might explain increased numbers of overweight U.S. infants? A mother’s weight gain during pregnancy and a mother’s own high weight before pregnancy may be factors (Catalano & Shankar, 2017). Also, an important factor likely is whether an infant is breast fed or bottle fed (Uwaezuoke, Eneh, & Ndu, 2017). Breast-fed infants have lower rates of weight gain than bottle-fed infants in childhood and adolescence, and it is estimated that breast feeding reduces the risk of obesity by approximatelyPage 115 20 percent (Uwaezuoke, Eneh, & Ndu, 2017).

Breast versus Bottle Feeding For the first four to six months of life, human milk or an alternative formula is the baby’s source of nutrients and energy. For years, debate has focused on whether breast feeding is better for the infant than bottle feeding. The growing consensus is that breast feeding is better for the baby’s health (Blake, Munoz, & Volpe, 2019; DeBruyne & Pinna, 2017; Thompson & Manore, 2018). Since the 1970s, breast feeding by U.S. mothers has soared (see Figure 11 ). In 2016, 81 percent of U.S. mothers breast fed their newborns, and 52 percent breast fed their 6-month-olds (Centers for Disease Control and Prevention, 2016). The American Academy of Pediatrics Section on Breastfeeding (2012) reconfirmed its recommendation of exclusive breast feeding in the first six months followed by continued breast feeding as complementary foods are introduced, and further breast feeding for one year or longer as mutually desired by the mother and infant.