Brain Development From Conception to Age 8 PDF

CHAPTER FOUR: BRAIN DEVELOPMENT FROM CONCEPTION TO AGE 8 After completing Chapter Four students will be able to: Identify the primary functions of the major areas of the brain Identify the primary functions of neurons Discuss the normal development of fetal b...

CHAPTER FOUR: BRAIN DEVELOPMENT FROM CONCEPTION TO AGE 8 After completing Chapter Four students will be able to: Identify the primary functions of the major areas of the brain Identify the primary functions of neurons Discuss the normal development of fetal brains Identify the six neural processes of development: cell proliferation: cell differentiation, cell migration, synaptogenesis, cell pruning, and myelination Discuss the normal trajectory of brain development from birth to age eight Discuss the concept of brain plasticity and its role in mediating non-normative events that hinder brain development The human brain is the most unique thing about each of us. It is home to our memories and our plans; we use it also for essential activities such as breathing and regulating our heartbeat, but we can also use it for making up bad jokes and excuses. Our brains help define who we are as individuals as our biology interacts with our environments. During the first eight years of life, the brain of a child is doing an enormous amount of work, day and night. In this chapter, we will explore the typical development of the human brain, starting at conception. To understand this development, we will need to delve into the inner workings of the brain, from the smallest parts of the neuron all the way up the four lobes of the cerebral cortex, where so much of our daily experience takes place. The brain plays an important role in all aspects of early development, and the experiences that happen early in life lay the foundation for how the brain will operate across the lifespan. For that reason, it is essential for anyone who is planning to work with infants, toddlers, and young children to understand the earliest stages and milestones of brain development. Ensuring that children’s brains get high quality input right from the start is the best way to ensure a lifetime of brain functionality. Earlier, we talked about the four domains of development: physical, cognitive, social, and emotional. The brain develops in each of these domains, just as every other part of the child does. Typically, the brain is most closely associated with cognitive development. Cognition, after all, is largely about brain functions such as memory, attention, processing speeds, and intelligence. When we talk about people who are smart, we often refer to them as having a “big brain” or being a “brainiac.” As will be discussed through this book, one of the most impressive cognitive feats of the brain is the development of spoken (and later written) language. But our brains also develop – and help guide development – in the other three domains as well. One of the primary functions of the somatosensory cortex of the brain is to accept, integrate, and act upon sensory information in the form of physical sensation. This narrow strip of the cerebral cortex is essential in nearly everything we do each day, helping us to know when we are touching objects, which in turn informs the systems that maintain our balance and orientation in space. These parts of the brain are necessary for learning to stand, walk, run, jump, and maybe even surf! Without the brain’s constant integration of important sensory information, our physical development would be significantly delayed (Jensen, 2019). Chapter Four: Brain Development from Conception to Age 8 | 71 72 | Chapter Four: Brain Development from Conception to Age 8 Biology of the Brain In order to understand what a child’s brain can do, it is important to first understand how the brain is built. Throughout gestation and into the first months of life, the brain of the infant is growing. Perhaps you have heard that the human brain is not fully developed until age 25? This is true, but the majority of the cellular development takes place in the first three years of life so that the next 22 years can be spent refining how those cells are used. In this section, we will explore the smallest part of the brain – the cells – and how networks between cells develop and become the brain from a biological perspective. There are six essential growth functions of your neural cells: cell proliferation, cell differentiation, cell migration, synaptogenesis, cell pruning, and myelination. In this section, you will learn the fundamentals of each of these processes, and throughout this textbook you will learn more about how these processes support children’s development in specific ages and stages. But first, let’s discuss what makes neural cells special, and how they work together to form the brain. Brain Cells: Neurons Like all living things, the brain is made of cells; brain cells are called neurons. Neurons are highly specialized cells that have three main parts: an axon, the cell body, and multiple dendrites. Electrical impulses run through these three structures in a specific pattern, causing chemical reactions which are our thoughts and feelings. These impulses also control our physical actions. Biology of the Brain | 73  The cell body is just like any other cell in the human body: it has a nucleus that houses DNA and RNA, which is surrounded by cytoplasm that contains organelles. In this picture, do you recognize any of the cellular structures from biology class? If it has been a while since you took Biology, or you just want a little more information, check out this Boundless Anatomy and Physiology course from Lumen! From this image, you may also be noticing several differences between a brain cell and other cells in the body. The most obvious characteristics of neurons that set them apart from other cells are their dendrites and long axons. In this illustration, the dendrites are the red branch-like structures extending from the main cell body. The dendrites are responsible for “touching” other cells – usually the axons of neighboring cells. You can see this depicted here where red branches are connecting to yellow branches, which come from a neighbor cell. Cells communicate with one another, passing along an electrical current that stimulates a chemical reaction. We perceive our thoughts and actions as instantaneous and smooth, but in reality our brains are constantly turning signals on and off in a wave like pattern! At the site where the two cells meet, a gap called the synapse, electrical currents pass from one cell to another. This is simply the name for the junction site between an axon and a neighboring dendrite, but a lot of important works takes place at a synapse! Electrical impulses move along an axon and when it reaches the synaptic cleft, it needs to “jump” from one neuron to another. The electrical current is moved across through a chemical reaction that produces a neurotransmitter – literally a chemical that transmits impulses between neurons. This electrical impulse travels from the dendrite, through the cell body, and down the axon to the next neurons. This is what we refer to as brain cells “firing.” Axons can be long relative to the size of an individual cell, allowing them to reach dendrites on neurons all around them. This can also make them fragile, so they need special protection (Konkel, 2018). Imagine wires in your own home, constantly moving electricity around to where it needs to be. There are places where two wires meet and electricity is transmitted from one to the next, just like between two neurons. Also, like the wires in your house, the physical structure that contains the electricity needs to be insulated to keep the electrical current inside the system and moving to where it needs to go. Axons are insulated by means of a myelin sheath, which is a thin layer of lipids (fatty substance) that protects the axon and helps insulate the electrical impulse as it moves. Without a healthy myelin sheath, it is possible for impulses to be slowed down or even lost altogether. 74 | Biology of the Brain  Electrical currents run the length of the axon with the help of the myelin sheath (Jensen, 2019). This image shows two neurons: the one on the left does not have a myelin sheath, while the one on the right does. Axons without myelin can still conduct signals, but the impulses move much more slowly. Follow this link to see an animated version of these two neurons conducting an impulse. Did you notice how much more slowly the impulse on the left was moving? Imagine you and your friend are walking down the sidewalk; each square of pavement is a myelin node. If one of you walks while the other one jumps from square to square, who will get to the end of the block first? The person who is jumping! This is how myelin nodes are able to move electrical impulses so much more quickly. They allow the current to “jump” along the axon, rather than moving in a slow, continuous wave. Neural Networks In the brain, single cells do have independent functions, but most neurons work in small clusters to accomplish a task or in larger clusters to control major functions of the body. For example, you have small but specialized areas of the brain that accept sensory information for each of the different parts of your body (see “temporal lobe” below) as well as an entire lobe that is devoted to visual information (see “occipital lobe” below). The size of an area and its density of neurons is related to how much work it needs to do. Generally speaking, we actively process and respond to significantly more visual information every day than we do to touch sensations. Neural cells gather together to form brain structures automatically, following a genetic blueprint that is almost universal. This is called “experience independent” development (Berninger & Richards, 2002) because it Biology of the Brain | 75 doesn’t require any sort of environmental input or experience. However, large portions of the brain grow only through experience, either “expected” or “dependent.” Expected experiences are those that the brain anticipates encountering – such as seeing the world for the first time- so it lays a foundation of neurons and then development continues based on what actually happens. in the child’s life. “Experience dependent” neural networks are those which only develop if and when a child has an experience that leads to their creation. For example, each person will develop a unique set of neural networks for their pets, their family members, their favorite ice cream sundae, and so on. While many of us might have similar networks, they will never be identical because not only do those networks consist of the memory of the specific thing (dog, mom, ice cream) they also consist of all of the emotions, language, and episodic memories that go with it. Episodic memories are memories of things that have happened to us; they are narrative in nature (they are a story) and often are tied to strong visual, olfactory, and sensory memories. As brain cells develop in utero, they become specialized for certain areas of the brain and follow genetically laid plans to move to the right areas and connect to other cells. You will read more about this later in this chapter, where we specifically talk about brain development in utero, but first it is important to understand what the areas of the brain actually are! Media Attributions Multipolar Neuron diagram © BruceBlaus via. Wikimedia Commons is licensed under a CC0 (Creative Commons Zero) license 76 | Biology of the Brain The Main Structures of the Brain Although we think of the brain as a single organ that floats in our skull all day, in reality the brain is made up of several distinct structures that have specialized jobs and that develop somewhat independently. As brain cells proliferate, they also become specialized for their future jobs as the place for making decisions in the brain. This is the process of cell differentiation. As cells become differentiated, they also must be located in the correct area: this is the process of cell migration. Once cells are in their specific area they become embedded in the physical structure as well as the functional structure of those areas (Berninger & Richards, 2002). The image below highlights the primary structures of the brain which are needed for full functioning: the spinal cord, the medulla oblongata, the cerebellum, the midbrain, and the cerebrum. Forebrain (cerebrum) Midbrain Pons Medulla Hindbrain oblongata (cerebellum) Spinal cord Spinal Cord The spinal cord connects the brain to the rest of the body. Medulla Oblongata This part of the brain is primarily responsible for life functions, including breathing, digestion, heart and blood vessel functioning, and swallowing. The medulla oblongata controls most of the involuntary actions that keep us alive, and damage to this part of the brain can be catastrophic. From its position at the top of the brainstem, the medulla oblongata helps connect the automatic portion of the central nervous system to the parts of the brain that process sensory, emotional, and memory input (Berninger & Richards, 2002). The Main Structures of the Brain | 77 Cerebellum The cerebellum, sometimes called the “little brain”, may be one of the smaller parts of the brain, but it contains the most neurons and plays an important role in how we interact with the world! It is a dense, butterfly-shaped organ at the base of the brain. If you place your hand on the back of your head and feel the area where your skull curves into your cervical spine, you are running your hand over your cerebellum. While the medulla oblongata controls involuntary functions, the cerebellum coordinates voluntary functions throughout your body, particularly motor functions. It takes in sensory information from the spinal cord and uses that to manage gross and fine motor control. Your cerebellum helps to keep you standing upright and helps you coordinate your motor skills in space and time. It is essential for walking and talking, and its health plays a significant role in how well children develop coordination as they grow (Berninger & Richards, 2002; Santrock, 2013). Normally, a cerebellum is considered essential to living a normal life; people who damage their cerebellum often experience dramatic declines in their coordination, balance, and ability to time their movements appropriately. It can be like losing control over all of your voluntary motor functions and always feeling uncoordinated. However, there have been cases reported of people who live completely normal lives without a cerebellum – if they are born that way! (Thomson, 2014) Pons Between the upper and lower parts of the brain is the Pons – a small area of brain that is responsible for relaying messages between the cerebellum and the cerebrum. Given what you have already learned about the function of the cerebellum, it should be no surprise that the pons is responsible for relaying information related to the voluntary functions that the cerebellum controls, as well as information about involuntary actions like sleep and respiration. Midbrain Sitting atop the pons is the midbrain, which is also a small area that plays an important role in relaying information around the brain, and ensuring proper functioning and communication. Cerebrum First, it is important to understand that the cerebrum is made up of two distinct hemispheres that mirror each other. The two hemispheres – right and left – process information from and exert control over opposite sides of the body. Your right hemisphere talks to the left side of your body, and vice versa. The main lobes of the brain are duplicated on each side, such that both the right and left hemisphere have the same areas (vision, sensory information, information processing, and speech) but the sides are complementary, not exact copies, meaning they do the same jobs but with different types of information. 78 | The Main Structures of the Brain Cerebral Cortex When you think of the brain, you are probably imagining the outermost layer, but this is only a portion of what makes up the human brain! Of course, that portion is responsible for a lot. The cerebral cortex is represented by the wrinkled layer in this picture of the brain that is primarily responsible for how we interact with the world around us. Frontal lobe Parietal lobe Temporal lobe Occipital lobe Brainstem Cerebral Cortex | 79  These two images both show the lobes of the brain, sometimes with added italicized labels. The ones above give you more details, so that you can have a better sense of what areas are associated with each lobe or what functions the areas have. The ones in italics show the functions of some areas. Let’s take a look at what each of the lobes of the brain is responsible for. 80 | Cerebral Cortex  Left visual Right visual fi e l d fi e l d Nasal retina Optical lens Te m p o r a l Te m p o r a l Eye retina retina Optic nerve Optic chiasma Lateral geniculate Pretectal nucleus (LGN) nucleus Primary visual cortex Occipital Lobe The occipital lobe is primarily responsible for integrating visual information. It may seem strange that the back of your brain is where information from your eyes is processed, but that is how your brain works! Even stranger still is that the left side of your brain is responsible for processing information from your right eye, and vice versa. Each eyeball has its own visual field from which information is gathered. This information is then sent across the midline of the brain, and into the occipital lobe where it is processed. People who have lost the connection between the two hemispheres of their brain experience significant changes to their visual field, and their ability to talk about what they see! Parietal Lobe The parietal lobe runs along the top of the brain just below where a headband might sit. It is where the majority of our sensory input is processed, including our senses of touch, taste, and temperature – all things that are essential for babies as they interact with the world around them! Cerebral Cortex | 81  The parietal lobe includes a specific strip known as the somatosensory cortex. Along this strip, the brain has designated areas that integrate sensory information from specific parts of the body. The name that has been given to this “body map” is the homunculus. As you can see in the image above, the somatosensory cortex is not an exact map, and there are some areas of the body that take up more areas of the brain than others. Remember: each hemisphere of the brain processes information from the opposite side of the body. That means that you have a map on either side of your brain, but each map coordinates information from the other half of your body (Berninger & Richards, 2002). Look carefully at the brain map; what do you notice about the amount of space given to different body parts? You probably noticed that your hands and face – especially your lips – take up a lot of space on the somatosensory cortex! Although it makes for a strange looking body map, this is actually very important to understand. Our face and our hands are essential for interacting with the world around us safely and accurately. Have you ever said “let me see that” but meant “Let me hold that in my hand” – that is because we “see” with our hands just as much as with our eyes, in terms of sensory information. Touching things tells us about the weight, 82 | Cerebral Cortex texture, and temperature of objects, as well as many other things. Our face is extremely sensitive because our head is where our eyes, ears, and brain all live – and we want to keep those things safe. Other areas of our body, such as our torso, get less neural space simply because this area tends to give us less essential information. It is also worth noticing that parts of the body where we often wear clothes tend to be areas with less sensory nerves. Think about how rarely you notice your clothes on your body compared to noticing a stray hair on your face! Temporal Lobe Located along the sides of your head, just above your ears, is your temporal lobe. Unlike the other three lobes of the brain, which obviously connect to one another across the midline of the brain, the temporal lobe appears to be two separate pieces, but is in fact connected through the middle of the brain and crosses the midline deep inside the cerebrum. It does this with the help of specific structures deep inside the brain, including the hippocampus (Berninger & Richards, 2002). It is not a coincidence that the temporal lobe is situated so close to the ear; it is in this part of the brain that speech and other sounds are processed. The image below shows the pathway of sounds, particularly language, around the temporal lobe. As you can see, once a word is “heard” (the acoustic phonetics) that sound information is split between parts of the temporal lobe that process sound information (lexical phonology) and a part that processes the meaning (lexical semantics) before all of that information makes it way into the hippocampus, where it is attached to memories and emotions, which help us to make sense of what we have heard! Cerebral Cortex | 83  Perhaps the most important aspect of the temporal lobe is the role that it plays in the reception and production of language. As you can see in the brain image above (motor and sensory regions), it is home to Wernicke’s and Broca’s areas – both regions of the brain that specialize in language. These two regions of the brain are located only in the left hemisphere of the temporal lobe, and work together to ensure speech production and comprehension. Wernicke’s area is important in the understanding of speech, while Broca’s area is related to speech production. For more information about each of these areas, check out these short videos about Wernicke’s Wernike’s and Broca’s areas respectively (Berninger & Richards, 2002; Berk, 2017). Frontal Lobe The frontal lobe is the last portion of the brain to fully develop, and that is largely because it is so dependent on experience. This is the part of your brain that is the “you.” Located in the front and center of your brain, this is where you make decisions, solve complex problems, interpret social cues, and monitor your own behavior. Although this part of the brain is present from birth, the vast neural networks that make up the frontal lobe are under construction for years – up to 25! Your frontal lobe is where most of the functions that translate into behaviors originate. While the three lobes of the brain are busy interpreting information from the body and the world, the frontal lobe allows us to make choices about what we do with that information and then to act based on those choices. This is referred to as executive functioning and the development of this part of the brain is essential for success in many aspects of life, including school. A significant piece of executive functioning is attention. Our attention system allows us to focus on a single thing or to divide our attention if necessary. Paying attention often means being able to block out information that is not important, often sensory information in the form of touch, sight, or sound. This means that before the attention system can fully develop, it is necessary for the sensory-information processing lobes in the brain to develop and learn to separate important from unimportant input. In infants, these systems are not yet developed, and it can take years until the attention system is fully functional. In the meantime, children may be easily distracted by sensory information that an adult would not notice, or would be able to ignore. As you will read later, not all children develop their attention system in the same way. Attention Deficit Disorder is a common diagnosis in childhood, and it is identified when a child has an underdeveloped attention system making it difficult to direct sustained focus on a single task. The executive function of the frontal lobe also includes our working memory. While our long-term memories are stored deep in the brain, our short term, or work, memory operates in the frontal lobe. This makes sense, since we want our working memory to be able to quickly and efficiently connect with our attention, problem solving, and social processes. That allows us to make decisions and monitor our behavior in the moment. Buried within the cerebral cortex are several areas that are responsible for managing memory and emotion. Without these parts of the brain, our emotional development would not be possible. The hippocampus, thalamus, and hypothalamus work together to help us remember emotional events and to make sense of the feelings that we have throughout the day. A major piece of early development is learning what feelings are, how to express them appropriately, and how to control them when necessary. The brain plays a significant role in all of this (Berninger & Richards, 2002). Media Attributions Brain Motor and Sensory Regions © :Blausen.com staff (2014). via. Wikimedia Commons is licensed under a CC BY-SA (Attribution ShareAlike) license 84 | Cerebral Cortex  Sensory Homunculus © OpenStax College, via. Wikimedia Commons is licensed under a CC BY-SA (Attribution ShareAlike) license Neural and functional organization of systems © Matthew H. Davis and M. Gareth Gaskell, via. Wikimedia Commons is licensed under a CC BY-SA (Attribution ShareAlike) license Cerebral Cortex | 85 Brain Development During Gestation Over the course of gestation, the brain grows rapidly and new neural cells grow at a rate of 50,000 to 100,000 per second between the 5th and 20th weeks. (Berninger & Richards, 2002; p79) This is where the six processes of neural development begin. At full-term birth, much of the neural foundation is complete and what comes next is to add on to the existing structure through experience. During the first three years of life, the brain will grow rapidly, adding millions of neuronal connections as it stores information from nearly every sensory, emotional, or cognitive experience. The brainstem, midbrain, and cerebral cortex will visibly develop during gestation. First, the brain stem develops, and it can be clearly distinguished from the other areas of the brain within the first month of gestation. At only four weeks into gestation, it is already possible to distinguish what will become the primary structures of the brain. This is due to rapid cell proliferation and differentiation. Proliferation is the generation of new neurons and their supporting cells, called glial cells. Differentiation refers to the shape and function of those cells, which become apparent as they grow. As they grow, neurons move around in the brain so that they are physically located in the areas where they are functionally compatible. This process is called cell migration. Genetic information within the nucleus of each cell determines what its function will be and tells it where to move. Cells move by attaching to tracks created by glial cells (helper cells) that provide a track for the neurons’ journey. (Berninger & Richards, 2002; p 80) Typically, cells in the cerebral cortex migrate from the inner layers of the brain outward, building the brain from the inside/ out – which should help to explain why the frontal lobe, somatosensory cortex, and even some areas related to language develop later than other areas of the brain. The brainstem, the bottom-most section in the lateral view, is responsible for moving information between the body – where sensory information originates – and the brain – where it is processed and commands are given to the body. It connects the body to the three primary information processing areas of the brain: the cerebellum, the midbrain, and the cerebrum. Brain development during gestation is influenced by a number of genetic and environmental factors. The overarching structure of the brain is independent of experience, being guided by genetic information from the beginning. Cell proliferation (the dividing of cells from a single cell into the trillions of cells that make up the human body) begins as soon as a fertilized egg embeds itself in the lining of the uterus, and cells continue to proliferate according to the instructions in each cell’s DNA. Of course, it is possible for DNA to give bad directions, and when this happens, the brain does not develop in the expected way. Environmental 86 | Brain Development During Gestation influences can damage DNA and cause irregularities in brain development. Perhaps one of the more well- known environmental causes of impaired brain development is from alcohol. Fetal Alcohol Spectrum Disorders are a family of diagnosable conditions that occur as a result of alcohol consumption during pregnancy. Although there are several physiological markers of FASDs, there are also many known cognitive side-effects due to the damage alcohol does to developing brain cells. Alcohol consumption is not the only way a pregnant woman can influence the brain development of her child. General health and nutrition are important to ensure that the mother’s body is able to direct adequate resources to fueling cell proliferation and the building of fetal organs, including the brain. As we mentioned above, the long axons on the end of neurons are covered by a fatty sheath called myelin. The developing brain needs fat to build this sheath, so mothers need to supply this through their own diet. Myelination of neural axons begins before birth, and at full gestation most of the spinal cord and brainstem are fully myelinated. However, myelination is not complete until adolescence! This means that although you may have the most neurons early in childhood, your brain works the quickest and most efficiently in your late teens and 20s. Throughout infancy, the midbrain and cerebellum are used regularly as infants learn to walk and talk; therefore, these areas receive the most myelination during the first two years of life. Yet the areas of the cerebral cortex, including the structures related to attention, language, and memory take up to ten years to be completely myelinated. Recall when you learned about the Emotional Domain of development, you read that the brain structures that underlie emotional regulation are not fully developed until later in life. This is because those areas are not fully myelinated, and myelination helps to strengthen their connections. Myelination requires a healthy diet with plenty of healthy fats. You may already know that infants need a full fat diet, but since myelination continues for nearly 18 years, nutrition is important at all stages of life. Now, let’s think about how this relates to infants and their brain development. Have you ever seen a baby explore the world? What are some of the strategies that they use? Media Attributions Brain Vesicle diagram © Openstax via. Wikimedia Commons is licensed under a CC BY (Attribution) license Brain Development During Gestation | 87 Brain Development in Infants and Toddlers Once infants enter the world, their brain is bombarded with information that fuels neural growth. During the first three years of life, cells proliferate, differentiate, and migrate at an incredible rate! As they arrive in their permanent network, they build connections with neighboring cells, and synaptogenesis occurs at each junction. Synaptogenesis is the building of connections between the end of one axon and the receptor of a neighboring dendrite. It is an essential part of cell growth, and as new cells proliferate and migrate into place, they are quick to find neighbors to connect with. Well into toddlerhood, neural cell proliferation continues to happen quickly and abundantly. Every experience for an infant or toddler is new, and therefore the brain chooses to use nearly all of them to build new network connections. It cannot be sure what will and what will not turn out to be important. Around age 3, the brain is as dense with neurons and neural connections as it will ever be throughout the lifespan! Creating a strong connection at a synaptic juncture is important to the lifespan of a neuron. Neurons that make weak or no connections cannot transfer impulses efficiently and tend to be removed in a process called pruning. But this density is hard to sustain, both in terms of keeping connections accessible and in terms of fueling the brain with nutrients and oxygen. Therefore, the brain needs to start disconnecting some of these neurons. This process is called pruning, because it is similar to what a gardener might do with a plant – carefully removing selected neurons in an effort to ensure better health for the most important ones. Pruning of neural networks continues throughout childhood and adolescence with different areas of the brain experiencing greater intensity of pruning at different times (Courage & Howe, 2002). In upcoming chapters, you will read more about the experiences that infants and toddlers have which help to support their brain development. As you learn about those important stages of childhood, keep in mind what is happening behind the scenes in each child’s brain! 88 | Brain Development in Infants and Toddlers Brain Development in Preschool and School-Age Children As was mentioned previously, the brain processes which begin before birth continue well into childhood, and some go until adolescence as well. Much of the brain’s rapid growth can be attributed to the experiences that children are having each day as they explore the world around them, interact with parents and caregivers, and grow physically. These early experiences are often informal in nature. This all changes when children enter more formal educational settings such as preschool and K-12 classes. Experiences once children begin to attend preschool become more intentionally designed to activate growth by providing children with experiences deemed essential for cognitive, social, and emotional development. For example, teaching children letter sounds and word meanings supports neural growth in their temporal lobe as it stimulates areas related to both receptive and productive language use. In preschool settings, children have opportunities to interact with peers of their own age, perhaps for the first time if they have been at home with a parent or caregiver since birth. These interactions are essential for triggering the synaptogenesis of neurons in the areas of the brain that help navigate social spaces, such as playing with friends. And as you just read, during this time myelination of the brain areas associated with better emotional control is taking place. Not all preschool age children attend a formal preschool class, but many do. For the ones who do not, brain development is still occuring at a furious rate, as children have other experiences with parents, caregivers, and peers in other settings. Even children who remain at home until Kindergarten have plenty of opportunities that fuel their neural growth – provided the adults in their life create such opportunities. As you will learn in upcoming chapters, many cognitive functions have critical periods for their development – times when the right experiences must occur in order for a function to develop. Language is one example of this; children who are not exposed to spoken or sign language in the first years of life will always struggle to learn the sounds and grammar of their language. Vision also has a critical period, and children with vision issues such as a “lazy eye” or non-binocular vision (meaning the two eyes don’t coordinate what they see across the midline of the brain) can only benefit from interventions up until about age 4. (Berninger & Richards, 2002; p 88) By school age, most children have had enough experiences to at least have fully functional brains and a healthy amount of connected neural networks. Children enter Kindergarten with a wide range of cognitive, social, and emotional abilities, but typically the physical structure of the brain is nearly identical to an adult’s brain. In school, children will learn to use their neural networks in the act of learning. As brain research continues to evolve, so does what and how much educators know about children’s brains. A great deal of “best practice” in early and elementary education is based on what we know about how the brain works and how to teach to that. For example, in this book you will learn more about multiple intelligences and learning styles, both based on brain research that recognizes that the four areas of the cerebral cortex take in different types of information (visual, sensory, auditory, and social-emotional). The best practice for educators that are associated with MI and learning styles is based on the idea that designing curriculum that matches how the brain already wants to process information is much more effective than trying to make children’s brains learn in less efficient ways. Brain Development in Preschool and School-Age Children | 89 90 | Brain Development in Preschool and School-Age Children