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5.1: Introduction

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    198000
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    Supporting Brain Development in Group Care

    If you were to enroll in a college class about infant and toddler development, would you expect to see a section on brain development? The importance of brain development in a child’s early years has been emphasized in the past few decades more than ever before; however, does brain development belong in a class on infants and toddlers, or should it only be included in classes that focus on older children? Most people will probably say “yes, the topic of brain development belongs in infant and toddler college classes”, but how would you explain your reasoning--why do you think brain development is so important during the first three years of life?

     

    displays the growth trajectory of gray matter and white matter in females (red) and males (blue)
    Figure \(\PageIndex{1}\): The graph on the left indicates 'Grey matter volume (mm^3)' on the y-axis, which ranges from 0 to 75. The x-axis represents age, starting from birth and progressing through 1 year, 2 years, 18 years, 35 years, to 80 years. The plot shows individual data points as well as a trend line. The trend line suggests that grey matter volume rapidly increases from birth, peaking around early childhood, and then gradually declines throughout the rest of the lifespan. The graph on the right shows 'White matter volume (mm^3)' on the y-axis, with values from 0 to 90. The age range on the x-axis is the same as the first graph. This plot also contains individual data points with a trend line. The white matter volume appears to increase from birth, reaching its peak around age 40, and then shows a slight decline or stabilization in later years. Both graphs include shaded areas around the trend lines that likely represent confidence intervals or variations in the data. Additionally, there are markers on the graph that seem to indicate the sample size at various ages, with larger triangles suggesting a larger sample size. These larger triangles are mostly seen at the beginning and the end of the age range, implying more data points collected at those ages.Overall, the data suggests an increase in both grey and white matter volumes during early development, with grey matter peaking earlier and then declining, while white matter volume peaks later in life and then either declines slightly or plateaus. Access table for complete Data[1]  

    If your answer focused on the rapid growth of the brain during the first three years, you are not alone in your thinking. This is how many people answer the question, and rightfully so. For example, take a look at Figure \(\PageIndex{1}\): that displays the growth trajectory of gray matter and white matter in females (red) and males (blue). Brain tissue can be divided into either white matter or gray matter. White matter regions are composed of axons. It appears white due to the myelin sheath on the axons (see Figure \(\PageIndex{1}\). Gray matter regions are composed of cell bodies and dendrites[1] [2]  (see Figure \(\PageIndex{1}\)[3] [4] . Gray matter is the location of most synapses–the connection sites where neurons communicate. As both charts show, but especially the chart for gray matter, brain growth in the first three years is rapid. [1]

     

    Dendrites surround a cell body which is connected by a myelin cord to the presynaptic terminals
    Figure \(\PageIndex{1}\): A typical neuron.  At the center of the neuron is the cell body containing the nucleus. Extending outward from the cell body are branch like projections structures called dendrites. One long, tube-like structure extends from the cell body as well, called the axon. Along the axon, there are periodic swellings which represent myelin. At the end of the axon, there are branching structures known as the presynaptic terminal.
     [3]

    The outer brain is composed of the cerebrum, cerebellum, and brainstem (see Figure \(\PageIndex{1}\). The cerebrum is the most prominent region of the brain and is organized into folds called gyri and grooves called sulci. The rapid growth in gray and white matter is paralleled by the rapid growth seen in total cerebrum volume (see Figure \(\PageIndex{1}\). [4]

    The cerebrum: Image described in caption.
    Figure \(\PageIndex{1}\): The brain features the Sulcus and gyrus on the front which is part of the cerebrum. Under the cerebrum is the cerebellum resting on top of the brainstem connected to the spinal cord. [5]

     

    Graph displaying rate of growth for gray matter volume peaks in infancy, at around five months of age. Figure caption describes image.
    Figure \(\PageIndex{1}\):Trajectories for total cerebrum volume for females (red) and males (blue). Access table for full data [6]

    Another way to examine the early rapid brain growth of white and gray matter and cerebrum volume is with Figure \(\PageIndex{1}\) (Bethlehem et al., 2022). Now, this figure has a lot going on, so let’s just focus on some important features. Similar to the previous figures, Figure \(\PageIndex{1}\) also charts the growth of white and gray matter across the lifespan; however, this figure adds when rate of growth (velocity) and size both peak. Rate of growth peaks are marked by circle icons and size peaks are marked by triangle icons.[1] [2]  The rate of growth for gray matter volume peaks in infancy, at around five months of age. The rate of growth for white matter volume peaks in toddlerhood, at around 2.4 years of age. Total cerebrum volume rate of growth peaks at approximately 7 months of age. All of this evidence makes it clear that in the first three years of life, the brain is rapidly growing, at rates unlike any other developmental period. A question to ponder is how much of this rapid growth is biologically driven, compared to experience-driven and can experiences, like differences in the quality of caregiving, play a role in this brain growth?

    see figure caption for full description

    Figure \(\PageIndex{1}\): A graphical summary of the normative trajectories of the median (50th centile) for each global MRI phenotype, and key developmental milestones, as a function of age (log-scaled). Circles depict the peak rate of growth milestones for each phenotype (defined by the maxima of the first derivatives of the median trajectories (Fig. 1e). Triangles depict the peak volume of each phenotype (defined by the maxima of the median trajectories); the definition of GMV:WMV differentiation is detailed in Supplementary Information 9.1. (Normative trajectories of brain growth.[7]

    The rapid brain growth during the first three years makes infancy and toddlerhood a sensitive period in human brain development (Gilmore, Knickmeyer, & Gao, 2018; Johnson & de Haan, 2015) because the brain development that happens during the first three years serves as the basis for future brain function and related behavioral outcomes (Bornstein, 2014; Kolb & Gibb, 2011; Tau & Peterson, 2010). Furthermore, the infant and toddler brain is highly plastic and changes in response to environmental inputs (Dawson et al., 2012; Hodel, 2018; Merz, Wiltshire, & Noble, 2019; Rebello et al., 2018; Tierney & Nelson, 2009). Although many brain development processes are guided largely by biological factors (Rakic, 1988), caregiving experiences can also shape brain development through experience-expectant and experience-dependent plasticity (Greenough, Black, & Wallace, 1987). [8] [9]

    References


    5.1: Introduction is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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