摘录

Your Baby's Amazing Brain Remember that feeling of excitement and exhilaration the day your baby was born? You examined her tiny face and gazed with amazement into her unaccustomed eyes wondering what she must be feeling in her first experience of the "outside" world. If you were like most new parents, while you believed she was the brightest, most beautiful baby ever born, you had to admit that she didn't yet seem to have much going on "upstairs." But as we are now learning, appearances can be deceiving. While you were smiling and saying hello, rubbing her tiny fingers and stroking her cheek, her brain cells were firing away, activating various regions of her brain like the lighting of a Christmas tree. Far from the passive little bundle she resembled, your baby was hard at work, actively constructing the foundations of her future intellectual and emotional self. Up until a few years ago, even infant researchers would have turned a skeptical eye on such a description. Now, however, with the help of incredible technology, scientists are able to actually observe physical activity in babies' brains. Dr. Harry Chugani, a pediatric neurobiologist at Wayne State University in Detroit, is one of the most experienced baby-brain watchers around. Using positron-emission tomography (PET) scanning, which displays various degrees of brain activity in an array of vivid colors, Dr. Chugani has been able to witness the bright red glow of brain-circuitry building in action. And what he is seeing supports the notion that, from the moment of birth, the environment into which a child is born begins to sculpt the brain in ways that will have long-lasting implications for its owner's future. Building a Brain Construction of this miracle organ we call our brain begins just weeks after conception, when fetal cells destined to become brain cells begin to multiply at the astonishing rate of about 250,000 per minute. Produced in the neural tube (which will eventually become the spinal cord), the neurons begin their journey to various regions of the brain, like dedicated soldiers, to perform their assigned tasks. By the time a baby makes her debut into the world, she will have an astronomical number of brain cells (or neurons) to begin her developmental journey toward adulthood. In fact, it is thought that all the neurons she will ever have are present at birth--a mind-boggling 100 to 200 billion. If newborns have all their neurons in place, why can't they read, write, or speak? The brain still must undergo substantial changes in order to meet the challenges that each child will face throughout her life. Only through brain growth and development does a child truly become a social, emotional, and intellectual being--one who is able to build new friendships, revel in the joy of a new puppy, and master the complexity of long division. One significant change that occurs in a young baby's brain is simply that it grows bigger. At birth a baby's brain weighs about 340 grams (about 12 ounces), and it continues to grow quite rapidly during the child's first few years. By her first birthday, her brain has already more than doubled in weight, to about 1,100 grams. Amazingly, by age five, brain weight will have reached about 90 percent of its eventual adult weight of 1,450 grams (almost 3 pounds). These increases in brain weight result both from cells growing larger and from the development of miles and miles of interconnective pathways that allow cells to communicate with one another. And as a baby's brain grows larger, dramatic changes take place in her ability to learn. Her memory becomes more functional, her language begins to develop, and her thinking skills are being continually refined. The various structures of a baby's brain are also undergoing significant changes. Located atop the spinal cord and below the cerebral cortex, the subcortical structures are primarily responsible for basic biological functions such as circulation, respiration, digestion, and elimination, and for a newborn's reflexive behaviors such as sucking. These subcortical structures must be fairly well developed at birth in order for a newborn to survive. But it is the development of the cerebral cortex that sets us humans apart from less intelligent animals. Advanced mental capabilities, such as thought, memory, language, mathematics, and complex problem solving, which are unique to human beings, are all made possible by the development of the cerebral cortex. The cerebral cortex is not only the largest part of our brain, it is also the part that most of us typically envision when we think of a human brain. The cerebral cortex includes our two cerebral hemispheres, each responsible for various higher-level functions. For example, the left cerebral hemisphere in most people is in charge of language, whereas the right cerebral hemisphere is more responsible for nonlanguage skills, such as recognizing familiar faces, finding our car in the mall parking lot, or sighing when we hear the melody of our favorite song. A newborn's cerebral cortex is relatively immature at birth compared to his subcortical structures. But as it grows in size and weight, begins to assign its cells specific jobs, and sets up patterns of connective circuitry, higher-level skills begin to emerge. It is the laying down of the neural wiring that connects each cell to a multitude of others that allows for the development of a mind. Making a Mind The "making" of a mind is all about neurons connecting with one another so that various parts of the brain can communicate. How do they do this? It mostly depends on the type of information that needs to be sent and the parts of the brain that need to receive it. Imagine you are living in California during the days of the wild, wild West when your first child is born. You can hardly wait to share the news with all your family. But sending birth announcements is somewhat difficult, to say the least, because most of your family members live in various states back East. You write a letter to your mother in Pennsylvania, your sister in Virginia, and your paternal grandmother in Tennessee. They in turn will send notes to various brothers, sisters, aunts, and uncles, who then send the news to a multitude of cousins and friends. The moment you deliver your letters to your local Pony Express station, your news begins its long journey across mountains and valleys, rivers and streams. With mailbags slung across his saddle, the rider gallops toward the next relay station. As he reins in his horse, he tosses his mailbags into the arms of new riders, who lunge toward their own transfer points. The process continues until mother, sister, and grandmother have received your message and, in turn, launch messages themselves, each contributing to the ever-growing network of your family's communication system. What exactly, you may be asking, does this have to do with baby minds? A child's developing neuronal circuitry works something like the Pony Express. Each neuron in a baby's brain grows a long taillike extension called an axon, which has many fingerlike structures at its end. Each neuron also has a corps of message receivers called dendrites. Dendrites are armlike structures that reach out from the neuronal body to take incoming messages to its neuron. Each neuron may have many, many dendrites and will generate new ones whenever the brain encounters new experiences. An axon's fingers reach out toward the receiver dendrites of other neurons but stop short of actually touching them--they just come very close. These remaining gaps, called synapses, are the ultimate conveyers of information throughout the brain. Excerpted from Baby Minds: Brain-Building Games Your Baby Will Love by Linda Acredolo, Susan Goodwyn All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.