Baby’s Brain Begins Now: Conception to Age 3
The fact that children are affected by their surroundings is too obvious to bear repeating. Child development specialists have produced decades of research showing that the environment of a child’s earliest years can have effects that last a lifetime.
Thanks to recent advances in technology, we have a clearer understanding of how these effects are related to early brain development. Neuroscientists can now identify patterns in brain activity that appear to be associated with some types of negative early experiences.1
But the long-term effects of early stress, poverty, neglect and maltreatment were well documented and virtually uncontested years before we could “see” them with brain scanning tools. So why should we need an understanding of brain development to show us how important children’s earliest experiences are for their well-being? Isn’t neuroscience just telling us what we already know?
Actually, there are several reasons why we should pay attention to the evidence provided by neuroscience. For instance, it may help us learn exactly how experiences affect children. This knowledge can aid our efforts to help children who are at risk and to undo, where possible, the effects of early adversity. Additionally, neuroscientists may help us learn when experiences affect children. If there are specific periods of vulnerability to certain types of experiences, then understanding these patterns will improve our attempts at intervention.
So far, neuroscience has not found conclusive answers to these questions. However, dramatic advances continue to be made in the field, and brain research continues to enhance education and intervention efforts. Accordingly, we have expanded this year’s Brain Development chapter to include additional information reflecting the latest scientific research.
We begin with a thumbnail sketch of brain anatomy, followed by a closer look at neurons and synapses, the brain’s communication specialists. We then discuss some unique features of early brain development and show how they make the first three years of life an especially critical period. Finally, we present an outline of brain development from conception to three, linking developmental events to the cognitive and behavioral changes associated with them.
An Overview of Brain Anatomy
The easiest way to get to know the brain is to learn the main structures of the adult brain and how they relate to its function (Figure 1). It should be kept in mind that the relationship between brain structure and function is never simple. Although we often hear claims about the “language area” or “emotion center” of the brain, statements like these are simplifications; in reality, even the simplest mental activities involve multiple brain regions.
The brain can be divided into three major parts. The brain stem, shaped like a widening stalk, connects the spinal cord to the upper brain. It controls reflexes and involuntary processes like breathing and heart rate. Behind the brain stem and below the upper brain is the cerebellum, which is involved in balance and coordination.
The cerebrum, the largest part of the brain, sits above the brain stem and cerebellum. While each of the brain’s structures plays an essential role, the cerebrum is the area most involved in higher processes like memory and learning. The cerebrum’s outer surface is called the cerebral cortex. Although less than one-fourth of an inch thick (in adulthood), it is where the brain’s most advanced activities – such as planning and decision-making – take place.
The folds of the cerebral cortex, which give the brain its wrinkled appearance, are an important feature of the brain’s structure. Appearing during prenatal development, these folds increase the surface area of the cerebral cortex and allow more of it to be “packed” inside the skull. The resulting ridges and grooves form a pattern that is essentially the same from person to person. The ridges are called gyri (singular=gyrus); the grooves are called sulci (singular=sulcus).
The Human Brain FIGURE 1
Source: Adapted from www.educarer.org, 2006.
Scientists use gyri and sulci to divide the cerebral cortex into smaller units called lobes. Each hemisphere has four lobes. The occipital lobes, at the back of the brain, control vision. The parietal lobes are associated with bodily sensations like heat, cold, pressure, and pain. The temporal lobes are involved with hearing, language skills, and social understanding, including perception of other people’s eyes and faces. The frontal lobes are associated with memory, abstract thinking, planning, and impulse control. The forward-most section of the frontal lobes is a distinct area referred to as the prefrontal cortex. This is the last brain area to mature, undergoing important developmental changes as late as adolescence. The prefrontal cortex is the location of our most advanced cognitive functions, including attention, motivation, and goal-directed behavior.2,3,4
Although our advanced cognitive abilities are dependent on the cerebral cortex, it is not the only part of the brain relevant to child development. The limbic system, located in the inner brain beneath the cortex, is a collection of small structures involved in more instinctive behaviors like emotional reactions, stress responses, and reward-seeking behaviors. The hippocampus is involved in memory formation and spatial learning. The hypothalamus is the control center for one of the body’s key stress systems, regulating the release of cortisol and other stress hormones. The amygdala evaluates threats and triggers the body’s stress response.2,5,6
Neurons and synapses form the wiring of the brain.
The brain processes information by forming networks of specialized nerve cells, called neurons, which communicate with one another using electrical and chemical signals (Figure 2). These messages are the physical basis of learning and memory.7 A neuron consists of a cell body and the branch-like structures that extend from it. These include multiple dendrites and an axon, which may have numerous axon terminals. The cell body is the neuron’s control center; among other duties, it stores DNA and generates energy used by the cell. The dendrites receive incoming signals from other neurons, and the axon and its terminal branches relay outgoing signals to other neurons. Axons are sometimes coated with myelin, a fatty substance that insulates the axon and increases the efficiency of communication.
Messages are passed between neurons at connections called synapses. The neurons do not actually touch, however. There is a microscopic gap – the synaptic cleft – between the axon terminal of one neuron and the dendrite of another. Communication between neurons involves complex electrical and chemical processes, but its basics can be outlined simply:
When a neuron (let’s call it Neuron A) receives a chemical signal from another neuron, Neuron A becomes electrically charged in relation to the surrounding fluid outside its membrane. This charge travels down its axon, away from the cell body, until it reaches the axon’s end. Waiting here inside the axon terminals are a group of storage sites, called vesicles, that contain chemicals manufactured and delivered by the cell body. When the electrical charge arrives at the axon terminal, it causes these vesicles to fuse with the terminal’s cell membrane, spilling their contents out of the cell and into the synaptic cleft.
As Neuron A returns to its resting state, the molecules it spilled – called neurotransmitters – make their way across the synaptic cleft to Neuron B’s dendrite. When they arrive, they bind with receptor sites in the dendrite’s membrane. Each time a neurotransmitter molecule from Neuron A binds with a receptor on Neuron B, ions from the fluid surrounding the cells enter Neuron B through the unlocked receptor. As a result, Neuron B develops an electrical charge, the charge travels down its axon, and the process continues.2
Communication Between Neurons FIGURE 2
Source: Adapted from www.educarer.org, 2006.
In the first three years, a child’s brain has up to twice as many synapses as it will have in adulthood.
Now that we’re a little more familiar with the fundamentals of the brain, let’s take a look at brain development in children. Between conception and age three, a child’s brain undergoes an impressive amount of change. At birth, it already has about all of the neurons it will ever have. It doubles in size in the first year, and by age three it has reached 80 percent of its adult volume.8,9,10
Even more importantly, synapses are formed at a faster rate during these years than at any other time. In fact, the brain creates many more of them than it needs: at age two or three, the brain has up to twice as many synapses as it will have in adulthood (Figure 3). These surplus connections are gradually eliminated throughout childhood and adolescence, a process sometimes referred to as blooming and pruning.11
Synapse Density Over Time FIGURE 3
Source: Corel, JL. The postnatal development of the human cerebral cortex. Cambridge, MA: Harvard University Press; 1975.
The organization of a child’s brain is affected by early experiences.
Why would the brain create more synapses than it needs, only to discard the extras? The answer lies in the interplay of genetic and environmental factors in brain development.
The early stages of development are strongly affected by genetic factors; for example, genes direct newly formed neurons to their correct locations in the brain and play a role in how they interact.12,13 However, although they arrange the basic wiring of the brain, genes do not design the brain completely.14,15
Instead, genes allow the brain to fine-tune itself according to the input it receives from the environment. A child’s senses report to the brain about her environment and experiences, and this input stimulates
Baby’s Brain Begins Now: Conception to Age 3The fact that children are affected by their surroundings is too obvious to bear repeating. Child development specialists have produced decades of research showing that the environment of a child’s earliest years can have effects that last a lifetime.Thanks to recent advances in technology, we have a clearer understanding of how these effects are related to early brain development. Neuroscientists can now identify patterns in brain activity that appear to be associated with some types of negative early experiences.1But the long-term effects of early stress, poverty, neglect and maltreatment were well documented and virtually uncontested years before we could “see” them with brain scanning tools. So why should we need an understanding of brain development to show us how important children’s earliest experiences are for their well-being? Isn’t neuroscience just telling us what we already know?Actually, there are several reasons why we should pay attention to the evidence provided by neuroscience. For instance, it may help us learn exactly how experiences affect children. This knowledge can aid our efforts to help children who are at risk and to undo, where possible, the effects of early adversity. Additionally, neuroscientists may help us learn when experiences affect children. If there are specific periods of vulnerability to certain types of experiences, then understanding these patterns will improve our attempts at intervention.เพื่อห่างไกล ประสาทวิทยาศาสตร์ไม่พบข้อสรุปคำตอบของคำถามเหล่านี้ อย่างไรก็ตาม ความก้าวหน้าอย่างมากต่อไปจะทำในฟิลด์ และวิจัยสมองยังคงส่งเสริมการศึกษาและความพยายามแทรกแซง ดังนั้น เราได้ขยายในปีนี้สมองพัฒนาบทเพื่อรวมข้อมูลเพิ่มเติมที่สะท้อนให้เห็นถึงการวิจัยทางวิทยาศาสตร์ล่าสุดเราเริ่มต้น ด้วยการร่างรูปขนาดย่อของกายวิภาคศาสตร์ของสมอง ตาม neurons และ synapses ผู้เชี่ยวชาญในการสื่อสารของสมอง เราอภิปรายคุณลักษณะเฉพาะบางอย่างของสมองเจริญ แล้วแสดงว่าพวกเขาทำให้สามปีแรกของชีวิตโดยเฉพาะอย่างยิ่งสำคัญรอบระยะเวลา สุดท้าย เรานำเค้าร่างของการพัฒนาสมองจากความคิดถึง สามเชื่อมโยงเหตุการณ์พัฒนาไปเปลี่ยนการรับรู้ และพฤติกรรมที่เกี่ยวข้องภาพรวมของกายวิภาคของสมองวิธีที่ง่ายที่สุดรับรู้สมองจะเรียนรู้โครงสร้างหลักของสมองผู้ใหญ่และว่ามีความสัมพันธ์กับหน้าที่ (1 รูป) จึงควรเก็บไว้ในใจว่า ความสัมพันธ์ระหว่างโครงสร้างของสมองและการทำงานไม่ได้ ถึงแม้ว่าเราได้ยินมักจะอ้างเกี่ยวกับ "ภาษาพื้นที่" หรือ "อารมณ์" ของสมอง งบดังมีศูนย์ลในเรื่องง่าย ในความเป็นจริง แม้ง่ายจิตใจกิจกรรมที่เกี่ยวข้องกับสมองหลายภูมิภาคThe brain can be divided into three major parts. The brain stem, shaped like a widening stalk, connects the spinal cord to the upper brain. It controls reflexes and involuntary processes like breathing and heart rate. Behind the brain stem and below the upper brain is the cerebellum, which is involved in balance and coordination.The cerebrum, the largest part of the brain, sits above the brain stem and cerebellum. While each of the brain’s structures plays an essential role, the cerebrum is the area most involved in higher processes like memory and learning. The cerebrum’s outer surface is called the cerebral cortex. Although less than one-fourth of an inch thick (in adulthood), it is where the brain’s most advanced activities – such as planning and decision-making – take place.The folds of the cerebral cortex, which give the brain its wrinkled appearance, are an important feature of the brain’s structure. Appearing during prenatal development, these folds increase the surface area of the cerebral cortex and allow more of it to be “packed” inside the skull. The resulting ridges and grooves form a pattern that is essentially the same from person to person. The ridges are called gyri (singular=gyrus); the grooves are called sulci (singular=sulcus). The Human Brain FIGURE 1Source: Adapted from www.educarer.org, 2006.นักวิทยาศาสตร์ใช้ gyri และ sulci คอร์เทกซ์ cerebral แบ่งหน่วยเล็กที่เรียกว่ากลีบ แต่ละซีกโลกมีสี่กลีบ กลีบท้ายทอย ทางสมอง ควบคุมวิสัยทัศน์ กลีบข้างขม่อมจะเกี่ยวข้องกับรู้สึกร่างกาย เช่นความร้อน เย็น ความดัน ปวด กลีบขมับจะเกี่ยวข้องกับการได้ยิน ภาษา และ เข้าใจสังคม รวมถึงการรับรู้ของตาและใบหน้าของคนอื่น กลีบหน้าผากจะเกี่ยวข้อง กับหน่วยความจำ ความคิดนามธรรม วางแผน ควบคุมกระแส ส่วนสุดข้างหน้าของกลีบหน้าผากคือ พื้นที่แตกต่างกันที่เรียกว่าคอร์เทกซ์ prefrontal อยู่บริเวณสมองสุดท้ายผู้ใหญ่ ผ่าตัดเปลี่ยนแปลงพัฒนาที่สำคัญช้าที่เป็นวัยรุ่น คอร์เทกซ์ prefrontal เป็นที่ตั้งของของเราทันสมัยที่สุดรับรู้ฟังก์ชัน ความสนใจ แรงจูงใจ และ behavior.2,3,4 โดยตรงเป้าหมายถึงแม้ว่าความสามารถการรับรู้ขั้นสูงของเราจะขึ้นอยู่กับคอร์เทกซ์ cerebral มันไม่ได้เฉพาะส่วนของสมองที่เกี่ยวข้องกับการพัฒนาเด็ก ระบบลิมบิก ในสมองภายใต้คอร์เทกซ์ คือ กลุ่มของโครงสร้างขนาดเล็กที่เกี่ยวข้องกับพฤติกรรมภาวะบอบบางอย่างเช่นปฏิกิริยาทางอารมณ์ ความเครียดการตอบสนอง และพฤติกรรมการแสวงหารางวัล ฮิพโพแคมปัสมีส่วนร่วมในการก่อตัวของหน่วยความจำและการเรียนรู้พื้นที่ Hypothalamus เป็นศูนย์ควบคุมระบบความเครียดที่สำคัญของร่างกาย ควบคุมของ cortisol และฮอร์โมนความเครียดอื่น ๆ Amygdala ประเมินภัยคุกคาม และทริกเกอร์ response.2,5,6 ความเครียดของร่างกายNeurons and synapses form the wiring of the brain.The brain processes information by forming networks of specialized nerve cells, called neurons, which communicate with one another using electrical and chemical signals (Figure 2). These messages are the physical basis of learning and memory.7 A neuron consists of a cell body and the branch-like structures that extend from it. These include multiple dendrites and an axon, which may have numerous axon terminals. The cell body is the neuron’s control center; among other duties, it stores DNA and generates energy used by the cell. The dendrites receive incoming signals from other neurons, and the axon and its terminal branches relay outgoing signals to other neurons. Axons are sometimes coated with myelin, a fatty substance that insulates the axon and increases the efficiency of communication.Messages are passed between neurons at connections called synapses. The neurons do not actually touch, however. There is a microscopic gap – the synaptic cleft – between the axon terminal of one neuron and the dendrite of another. Communication between neurons involves complex electrical and chemical processes, but its basics can be outlined simply:When a neuron (let’s call it Neuron A) receives a chemical signal from another neuron, Neuron A becomes electrically charged in relation to the surrounding fluid outside its membrane. This charge travels down its axon, away from the cell body, until it reaches the axon’s end. Waiting here inside the axon terminals are a group of storage sites, called vesicles, that contain chemicals manufactured and delivered by the cell body. When the electrical charge arrives at the axon terminal, it causes these vesicles to fuse with the terminal’s cell membrane, spilling their contents out of the cell and into the synaptic cleft.As Neuron A returns to its resting state, the molecules it spilled – called neurotransmitters – make their way across the synaptic cleft to Neuron B’s dendrite. When they arrive, they bind with receptor sites in the dendrite’s membrane. Each time a neurotransmitter molecule from Neuron A binds with a receptor on Neuron B, ions from the fluid surrounding the cells enter Neuron B through the unlocked receptor. As a result, Neuron B develops an electrical charge, the charge travels down its axon, and the process continues.2 Communication Between Neurons FIGURE 2Source: Adapted from www.educarer.org, 2006.In the first three years, a child’s brain has up to twice as many synapses as it will have in adulthood.Now that we’re a little more familiar with the fundamentals of the brain, let’s take a look at brain development in children. Between conception and age three, a child’s brain undergoes an impressive amount of change. At birth, it already has about all of the neurons it will ever have. It doubles in size in the first year, and by age three it has reached 80 percent of its adult volume.8,9,10Even more importantly, synapses are formed at a faster rate during these years than at any other time. In fact, the brain creates many more of them than it needs: at age two or three, the brain has up to twice as many synapses as it will have in adulthood (Figure 3). These surplus connections are gradually eliminated throughout childhood and adolescence, a process sometimes referred to as blooming and pruning.11
Synapse Density Over Time FIGURE 3
Source: Corel, JL. The postnatal development of the human cerebral cortex. Cambridge, MA: Harvard University Press; 1975.
The organization of a child’s brain is affected by early experiences.
Why would the brain create more synapses than it needs, only to discard the extras? The answer lies in the interplay of genetic and environmental factors in brain development.
The early stages of development are strongly affected by genetic factors; for example, genes direct newly formed neurons to their correct locations in the brain and play a role in how they interact.12,13 However, although they arrange the basic wiring of the brain, genes do not design the brain completely.14,15
Instead, genes allow the brain to fine-tune itself according to the input it receives from the environment. A child’s senses report to the brain about her environment and experiences, and this input stimulates
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