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Figure 2.1 Cortical connections over two years adapted from Conel The top row shows the baby’s cortex at birth, then at one month and at three months. They all look about the same, don’t they? But look what happens at six months (bottom left box): the number of cell bodies remains the same, but the number of connections has multiplied exponentially. The connections grow so quickly in the first three years of life that neuroscientists call it neural exuberance. Neural exuberance! The name is well earned: The baby’s brain makes 24 million new connections every minute, and this continues for the first three years of life. Each neuron may be connected to 1,000 other neurons — that multiplies out to 100 trillion possible connections between neurons, more than the number of stars in the universe. This high level of connectivity between brain cells leads to the cortex of a three-year-old being twice as thick as an adult’s! As connections are created, new abilities emerge. For example, when connections grow in Broca’s area — speech production — around six months, then children begin to speak. Around nine months of age, the frontal areas (behind the forehead) become more interconnected, and that’s when most children develop object permanence: knowing that objects continue to exist even when they are out of sight. Before object permanence develops, when Mom is out of sight she’s no longer in the baby’s universe. This is why young babies are inconsolable when Mom leaves. Once they start to develop object permanence, babies can hold on to an internal image of Mom. This is about the age that babies play peek-a-boo. Mom disappears when she puts the blanket over her head, but the nine-month-old knows Mom’s still there even if he can’t see her. The infant tests his “knowledge” when he pulls the blanket off and sees — sure enough! —Mom really is there! What is the use of so many brain connections in the first three years of life? These connections are ready-made highways for information to travel along. The toddlers’ ability to quickly adapt and learn is possible because they have a vast number of brain connections available for making sense of the world. Thanks to neural exuberance, the child does not need to create connections on the spur of the moment to make meaning of each new experience; myriad connections are already there. Pruning of connections The number of connections remains high from age 3 until age 10, when the process of neural pruning begins. Connections that are being used remain; others get absorbed back into the neuron. It’s similar to pruning a bush. After pruning, individual branches get thicker, fruit is more abundant, and the whole bush gets fuller. This seems a little counter-intuitive, but pruning works because it allows the plant’s limited resources to go to its strongest parts; water and nutrients are no longer wasted on spindly branches and dried-out roots. Similarly, when unused brain connections are pruned, neural resources are more available for brain areas that are being used. This results in a more useful and efficient brain that’s tailor-made to meet each individual’s needs. This process of pruning occurs in all brain areas. Figure 2.2 presents findings published by Sowell and associates. They measured Magnetic Resonance Imaging in 176 normal subjects from age 7 to 87 years. The x-axes in these graphs present years from 10 to 90 years. Notice there is a common pattern of decreasing connections in all brain areas. In some brain areas this change is steeper, such as in frontal areas, but is flatter in other areas such as temporal areas in the left hemisphere.
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