NATURAL SCIENCE: This passage is adapted from the article “How to Build a Baby’s Brain” by Sharon Begley (©1997 by Newsweek, Inc.). In this selection, the term neuron refers to a specialized cell of the nervous system, and tomography refers to a method of producing three-dimensional images of internal structures.
自然科学：这篇文章改编自“如何构建一个婴儿的大脑”一文(©1997 by Newsweek，Inc.)，在该选择中，术语“神经元”是指神经系统的特殊细胞，断层摄影术是指产生内部结构的三维图像的方法。
HOW TO BUILD A BABY’S BRAIN(如何构建一个婴儿的大脑)
『1』You cannot see what is going on inside your new-born’s brain. You cannot see the electrical activity as her eyes lock onto yours and, almost instantaneously, a neuron in her retina makes a connection to one in her brain’s visual cortex that will last all her life. The image of your face has become an enduring memory in her mind. And you cannot see the explosive release of a neurotransmitter—brain chemical—as a neuron from your baby’s ear, carrying the electrically encoded sound of “ma,” connects to a neuron in her auditory cortex. “Ma” has now commandeered a cluster of cells in the infant’s brain that will, as long as the child lives, respond to no other sound.
『2』You cannot see any of this. But Dr. Harry Chugani can come close. With positron-emission tomography (PET), Chugani, a pediatric neurobiologist, watches the regions of a baby’s brain turn on, one after another, like city neighborhoods having their electricity restored after a blackout. He can measure activity in the primitive brain stem and sensory cortex from the moment the baby is born. He can observe the visual cortex burn with activity in the second and third months of life. He can see the frontal cortex light up at 6 to 8 months. He can see, in other words, that the brain of a baby is still forming long after the child has left the womb—not merely growing bigger, but forming the microscopic connections responsible for feeling, learning and remembering.
你看不出这有什么。但是，哈里·库贾尼博士可以接近。有了正电子发射层析成像(PET)，儿童神经生物学家Chugani观察到一个接一个的婴儿大脑的区域，像停电后恢复电力的城市社区。从宝宝出生的那一刻起，他可以测量原始脑干和感觉皮层的活动。他可以在生命的第二个月和第三个月内观察活动的视觉皮质烧伤。 他可以在6到8个月内看到额叶皮质亮起。 换句话说，他可以看到一个婴儿的大脑还在孩子离开子宫后不久就形成 - 不仅仅是增长更大，而且形成了对感觉，学习和记忆负责的微观连接。
『3』Scientists are just now realizing how experiences after birth, rather than something innate, determine the actual wiring of the human brain. Only 15 years ago neuroscientists assumed that by the time babies are born, the structure of their brains had been genetically determined. But by 1996, researchers knew that was wrong. Instead, early-childhood experiences exert a dramatic and precise impact, physically determining how the intricate neural circuits of the brain are wired. Since then they have been learning how those experiences shape the brain’s circuits.
『4』At birth, the brain’s 100 billion or so neurons form more than 50 trillion connections (synapses). The genes the baby carries have already determined his brain’s basic wiring. They have formed the connections in the brain stem that will make the heart beat and the lungs respire. But that’s not all. Of a human’s 80,000 different genes, fully half are believed to be involved in forming and running the central nervous system. Yet even that doesn’t come close to what the brain needs. In the first months of life, the number of synapses will increase 20-50 fold—to more than 1,000 trillion. There simply are not enough genes in the human species to specify so many connections.
出生时，大脑的1000亿左右的神经元形成超过50万亿的连接(突触)。婴儿携带的基因已经确定了他的大脑的基本接线。 它们形成了脑干中的连接，使心脏跳动和肺部呼吸。 但这不是全部。在人类的8万种不同基因中，完全有一半被认为参与中枢神经系统的形成和运行。然而，即使这并不接近大脑所需要的。 在生命的头几个月，突触的数量将增加20-50倍至超过1000万亿。这里根本就没有足够的基因在人类中指定如此多的连接。
『5』That leaves experience—all the signals that a baby receives from the world. Experience seems to exert its effects by strengthening synapses. Just as a memory will fade if it is not accessed from time to time, so synapses that are not used will also wither away in a process called pruning. The way to reinforce these wispy connections has come to be known as stimulation. Contrary to the claims of entrepreneurs preying on the anxieties of new parents, stimulation does not mean subjecting a toddler to flashcards. Rather, it is something much simpler—sorting socks by color or listening to the soothing cadences of a fairy tale. In the most extensive study yet of what makes a difference, Craig Ramey of the University of Alabama found that it was blocks, beads, peekaboo and other old-fashioned measures that enhance cognitive, motor and language development and, absent traumas, enhance them permanently.
这将留下宝贵的经验 - 婴儿从世界获得的所有信号。经验似乎通过加强突触来发挥作用。就像记忆会随着时间的推移而消失，所以未被使用的突触也会在称为修剪的过程中消失。加强这些弱小连接的方法已经被称为刺激。与新生父母担心的企业家的要求相反，刺激并不意味着让一个孩子进入闪卡。相反，它是一个更简单的颜色分选袜子或听童话的舒缓的节奏。在最广泛的研究之中，阿拉巴马大学的克雷格·拉米(Craig Ramey)发现，它是阻碍，珠子，躲猫猫和其他老式的措施来增强认知，运动和语言发展，缺少创伤，增强他们永久。
『6』The formation of synapses (synaptogenesis) and their pruning occurs at different times in different parts of the brain. The sequence seems to coincide with the emergence of various skills. Synaptogenesis begins in the motor cortex at about 2 months. Around then, infants lose their “startle” and “rooting” reflexes and begin to master purposeful movements. At 3 months, synapse formation in the visual cortex peaks; the brain is fine-tuning connections allowing the eyes to focus on an object. At 8 or 9 months the hippocampus, which indexes and files memories, becomes fully functional; only now can babies form explicit memories of, say, how to move a mobile. In the second half of the first year, finds Chugani, the prefrontal cortex, the seat of forethought and logic, forms synapses at such a rate that it consumes twice as much energy as an adult brain. That furious pace continues for the child’s first decade of life.
突触的形成(突触发生)及其修剪发生在不同时间的脑部不同部位。这个序列似乎与各种技能的出现相吻合。 突触生成在大约2个月的运动皮层开始。在那时，婴儿失去了他们的“惊吓”和“生根”的反应，开始掌握有目的的动作。在三个月的时间里，视皮层突触形成峰值; 大脑是微调连接，允许眼睛聚焦在一个物体上。在8或9个月时，海马的索引和文件记忆变得充分发挥作用; 只有现在，婴儿可以形成明确的回忆，比如说如何移动手机。在第一年的下半年，发现Chugani，前额叶皮层(前额叶皮层)形成了突触，在这样的速率下，它消耗的能量是成年人大脑的两倍。这一疯狂的步伐继续着孩子生命的第一个十年。