Discover more from The Scando Review
Development of the brain
A common misconception about the brain is that it fully matures within the first few years of life and that its development can be best aided by bombarding it with as much stimulation as possible—reading instruction, violin lessons, art classes, and so on—before the owner reaches kindergarten. That could not be further from the truth. Although the brain develops rapidly before birth and in the first few years after birth, it continues to grow throughout childhood, adolescence, and early adulthood. To be sure, the early years are crucial, but the kinds of experiences that foster the brain's early development are fairly common.
Development During Pregnancy
The brain appears as a tiny tube about 25 days after conception. The tube lengthens and begins to fold inward to form pockets (Rayport, 1992). Three chambers appear, which later develop into the forebrain, midbrain, and hindbrain. Neurons form and reproduce rapidly in the inner part of the tube, at an astonishing rate of 50,000 to 100,000 new cells per second between the 5th and 20th weeks of prenatal development (M. Diamond & Hopson, 1998). The vast majority of neurons a person will ever have, but not all, are formed during this time (Bruer, 1999; C. A. Nelson, Thomas, & de Haan, 2006; R. A. Thompson & Nelson, 2001).
During the second trimester of prenatal development, neurons migrate to various locations, drawn by a variety of chemicals and supported by glial cells. When they arrive, they send out dendrites and axons to connect with one another. Those who make contact survive and begin to take on specific roles, while those who do not (roughly half of them) die off (M. Diamond & Hopson, 1998; Goldman-Rakic, 1986; Huttenlocher, 1993). Such deaths, however, are not to be lamented. Humans being programmed to overproduce neurons appears to be Mother Nature's way of ensuring that the brain has a sufficient number with which to work. The excess ones are unnecessary and can be safely discarded.
Development in Infancy and Early Childhood
Between birth and age three, the brain more than triples in size, with glial cell proliferation accounting for the majority of the increase (Koob, 2009; Lenroot & Giedd, 2007). The cerebral cortex is the least mature part of the brain at birth, and cortical changes during infancy and early childhood are likely to account for many of the improvements in children's thinking, reasoning, and self-control (M. A. Bell, Wolfe, & Adkins, 2007; M. I. Posner & Rothbart, 2007; Quartz & Sejnowski, 1997). Synaptogenesis, differentiation, synaptic pruning, and myelination are all important processes in early brain development.
Synapses are formed by neurons long before birth. However, the rate of synapse formation accelerates dramatically shortly after birth. Neurons grow new dendrites that branch out in all directions, bringing them into contact with a large number of their neighbours. Young children have many more synapses than adults because of this process of synaptogenesis. The rapid proliferation of synapses eventually comes to a halt. Synapses reach their peak in the auditory cortex (temporal lobes) at about 3 months, in the visual cortex (occipital lobes) at about 12 months, and in the frontal lobes at about 2 or 3 months (Bauer, DeBoer, & Lukowski, 2007; Bruer, 1999; Byrnes, 2001; Huttenlocher, 1979).
As neurons form synapses with one another, they also begin to take on particular functions (McCall & Plemons, 2001; Neville & Bruer, 2001). Through this process, known as differentiation, neurons become specialists, assuming some duties and steering clear of others.
Pruning of synapses
Because children are exposed to a wide range of stimuli and experiences in their daily lives, some synapses come in handy and are used frequently. Other synapses are mostly irrelevant and useless, and they disintegrate gradually—a process known as synaptic pruning. In fact, the system appears to be designed to ensure that synaptic pruning occurs. Neurons require trophic factors, which are chemical substances, for survival and well-being, and by transmitting messages to other neurons, they cause the recipients to secrete such chemicals. When neurons receive trophic factors from the same sources on a regular basis, they form stable synapses with those sources. They pull their axons away from "unsupportive" neurons if they receive trophic factors from some but not others.
As previously stated, the axon of a neuron is sometimes covered with a myelin sheath, which greatly accelerates the rate at which an electrical charge travels along the axon. Myelin is not present when neurons first form; it is introduced later by glial cells. Myelination, the process of coating neural axons, occurs gradually over time. Some myelination occurs near the end of the prenatal period (for example, in areas required for basic survival), but the majority occurs in the first few years after birth, with different areas becoming myelinated in a predictable sequence (M. Diamond & Hopson, 1998). Myelination, without a doubt, improves the brain's ability to respond to the outside world quickly and efficiently.
Messages are transmitted through the human nervous system via (1) electrical transmissions that run through individual neurons and (2) chemical transmissions that cross synapses between neurons. Synapses in the spinal cord are responsible for a few basic reflexes, but the brain is the body's coordination and decision-making centre.
Scientists have learned a lot about how the brain works by employing a growing arsenal of research methods. In humans, the forebrain—the largest and most recently evolved part of the brain—predominates in consciousness, thinking, learning, and the many distinctly human mental activities in which people engage. Even seemingly simple tasks (for example, recognising and understanding a specific word) typically involve many parts of the brain.