0:07 Today we are going to focus on physical development, changes from the prenatal period to age three years. And when we talk about physical development, I'm going to be referring to three aspects of this domain. First, prenatal development. Second is physical growth in the body in weight and height. And third are changing motor skills. The prenatal period is a time of rapid progression. The developing fetus is getting prepared for life outside the womb. It's developing, it's moving about, it's hearing, tasting, and so forth. And these practices within the womb provide the baby with what it needs when it will adapt outside the womb. There are
0:53 very many things going on in fetal development that we refer to as actually learning. This is the beginning of learning. This is when the fetus is engaging with a very rich sensory environment of the womb. The fetus actually breathes, swallows, tastes, and hears. It engages much movement that actually prepares the limbs for outside. The fetus is engaging in spontaneous movements, flailing its arms, kicking its feet, even starting to move its hands toward the face. By about 19 to 35 weeks of age, half of the fetus's arm movements are the hand to the mouth, to kind of suck on the mouth and thumb. And these have been actually considered some of the very first goal-directed actions
1:38 of human development. And the fetus is also hearing and actually remembering the things that it hears. So the uterine environment, it's brimming with sounds, all kinds of sounds, including the sounds of the voices of the caregivers outside the womb. So by five to six months of age, the fetus begins to respond to sound. And then toward the end of the fetal period, the sounds the baby hears are actually remembered. Two-day-old newborns, they will attend to recordings of their mother's voice more so than to recordings of other people's voice, another woman's voice, or even to lullabies that mother played during late pregnancy. So this shows that not only is the fetus hearing in the final trimester, but it's remembering the experiences that it did hear. There's
2:28 also great brain development going on in the developing fetus. From the period of zero through birth and then birth through age three, that entire span, on average there are 700 neural connections developing every second. In fact, there's an overproduction of neurons so that the infant is adaptive to a wide range of environments. And depending on particular environmental influences, there will be what we call a pruning of neurons. The brain becomes specialized for certain experiences and not others. And this specialization is very common in early childhood, more so than in adulthood. Therefore, we use the term plasticity. The brain in early development is very sensitive to both
3:15 enrichment and adversity in the environment from ages 0 to 3 than it is later in development. I'd like to show you a slide that depicts the developing brain through three years of age. And you'll see that there's different regions of the brain developing at different times in development. So for example, the sensory pathways, vision and hearing, are the earliest to develop. And then the hemispheres associated with language and speech sounds develop a bit later. And then those associated with higher cognitive function are occurring even later in development. But what you might notice from this chart is that the first year of life is such an important time of rapid development in these regions of the brain. So let me turn now
4:05 to talking about normative growth, changes to physical body and to weight and height. Here's a normative growth chart that shows different curves for children who are showing average growth and low growth and above average growth. So the World Health Organization defines one set of global standards for growth. And in the slide, what you're looking at is height for age in children from birth to two years of age. So the middle line is showing those children who are typically developing, that's the green line, and just below the green line is what we refer to as moderate stunting. That's the idea that height for age is lower than
4:51 the normative path. The lowest line is what we refer to as severe stunting, which is three standard deviations below the mean. Now this is the chart for boys. And here you have the chart for girls. And again, you see the green line representing the average growth and the black line representing severe stunting of three standard deviations below the mean. This next figure shows how stunting emerges in the first 1,000 days after birth. If you look all the way to the left-hand side, you'll notice that at birth, most newborns are in a very narrow normal range. There is very little wasting, there's little underweight, and there is little stunting. But now let's look specifically specifically at the blue line, the one that shows the steepest decline over time.
5:40 And this line shows in the first thousand days of development in certain countries there's extreme stunting in children. By two years of age, children show nearly two standard deviations below the average for where they should be. This is largely the case of severe undernutrition that is common in many of these middle low and middle income countries and this actually creates harmful context for children's physical development. So what are some of the influences on weight and height? Obviously prenatal experiences matter, the mother's own nutrition matters, the kind of prenatal care a mother receives is important. Also we know that even postnatal experiences such as touch could be very important for putting on
6:27 weight. There's been some work with what we refer to as kangaroo care, which is extensive skin-to-skin contact that was implemented with premature babies in India. And it was found when there was a lot of intervention around skin-to-skin contact that those premature babies ended up growing quicker, showing lower mortality and lower rates of disease. So we do know that environment of touch is important to development. It's also important that the baby receives the nutrients and the micronutrients necessary for body growth. And clearly water and sanitation are important as well. Breastfeeding is a very important aspect of nutrition that aids children's physical development, as is responsive feeding. So the benefits to infants from breastfeeding, particularly exclusive breastfeeding
7:17 in the first six months of life, is development of a stronger immune system, lower diarrheal and other GI infections, greater growth in weight and height, a lower likelihood of transmission of HIV to the child, and all of these factors are in turn linked to higher cognitive skills. After introduction of solid foods, what is found is that responsive feeding is important. A parent who pushes food and forces food on a child, that is not good, just as being insensitive to cues of hunger is not good for the child. I'd like to now turn to the idea of motor skills. As children's bodies are
8:03 changing, so are their abilities to crawl, sit, stand, walk, and so forth. We distinguish between two broad categories of motor skills. The first are fine motor skills. Those are the movements that involve very small muscles of the body, like hands and fingers for writing, grasping, touching, holding. And gross motor skills are due to the large muscles of the body, such as arms, legs, and head. That would be something like standing upright, crawling, walking, and running. And it is important not only to engage in these movements, to be able to coordinate these movements with vision and perception, so babies see obstacles in their path and can navigate around them. So one of the questions we have
8:48 concerning the development of these different skills is when do we expect certain motor milestones to occur? When do we think children should be sitting up, walking, crawling, and so forth? And we could trace some of the earliest research on infant motor development to the work of Arnold Giselle. Arnold Giselle documented the development of milestones in babies by bringing them to the lab and kind of presenting them with all different toys for manipulation, kind of watching their spontaneous movements and behaviors. And what he did from this is he documented across age the kind of skills that will emerge at different ages Here you'll see that the horizontal line represents the range of age when a skill will emerge. You'll notice there's a large window of time when each of these motor
9:37 skills emerges. The little vertical line in the middle of that refers to the average, the on average when particular skills emerge. And we can see that all the way from prone all the way up to walking, that there's wide variability or heterogeneity around motor skills. One of the critiques of Giselle's work by contemporary researchers is the idea that it was normed on white middle-class babies in New Haven, Connecticut, and a small sample at that. we do know that there's huge environmental influences on height and weight and physical development and similarly on motor development. So is it really correct to have these norms at particular ages? What happens if we go to other cultural communities? What we actually find is that researchers who have gone around the world to look
10:25 at practices in child rearing and cultures such as Bali and Mali and Tajikistan and Cameroon and so forth, Find very different practices that can either speed up motor development or slow it down and impede motor progress. One example is the work by Brondeen Brill in Molly, and she found that caregivers, they actually stretch babies' arms and they pull the legs and suspend babies and actively exercise their muscles all the time, every day. And these kind of exercises actually are found to promote the onset of earlier motor milestones in that cultural community. So to summarize physical development, learning is beginning to occur already in the prenatal environment. Brains are wired in a way for learning,
11:16 but there are sensitive periods around different skills occurring at different times in the regions of the brain. So vision and perception is emerging earliest, language and higher cognitive functions later in terms of the brain regions that are implicated in those skills. Sensitivity to the early environment is extremely high in the first years of life as the brain's neuronal architecture is so rapidly developing.
