and prepare young children to start school ready to learn:
* Brain development that takes place prenatally, and in the first years of life, is more rapid and extensive than previously realized
* Brain development is much more vulnerable to environmental influence than ever before suspected
* The influence of early environment on brain development is long-lasting
* The environment affects not only the number of brain cells and the number of connections among them, but also the way these connections are "wired"
* New scientific evidence exists concerning the negative impact of early stress on brain function. (Carnegie Corporation, 1994, p. 2)
The findings of brain development research are astounding. In fact, "the discoveries are so profound that many researchers say we will surely look back on the 1990s as the 'Decade of the Brain'" (Simmons & Sheehan, 1997, p. 1). Moreover, the brain development research findings have serious implications for parents and policymakers (Nash, 1997).
According to Carla Shatz of the University of California, Berkeley, "There are two broad stages of brain wiring; an early period [prenatal], when experience is not required, and a later one, when it is" (Begley, 1996). She continues:
In the beginning, the brain-to-be consists of only a few advance scouts breaking trail: within a week of conception they march out of the embryo's "neural tube," a cylinder of cells extending from head to tail. Multiplying as they go (the brain adds an astonishing 250,000 neurons per minute during gestation), the neurons clump into the brain stem, which commands heartbeat and breathing, build the little cerebellum at the back of the head, which controls posture and movement, and form the grooved and rumpled cortex wherein thought and perception originate. (p. 61)
This hardwiring, which begins as early as a week after conception, provides the basic foundation of brain development, which in turn controls respiration, reflexes, and heartbeat (Begley, 1996; Begley, 1997; Lach, 1997).
While the brain connections developed before birth are crucial, their primary purpose is biological (Simmons & Sheehan, 1997). It is during the child's first months and years of growth and development that nature and nurture mesh, until they become "intertwined and inseparable" (Simmons & Sheehan, 1997, p. 6). When a child is born, his brain has 100 billion neurons, which in turn make over 50 trillion synapses (Begley, 1997). Afterwards, especially within the first three years of life, the brain undergoes a series of phenomenal changes. During this period, many more connections among neurons are created - literally trillions more than the brain can possibly use. Over time, those connections that are seldom or never used are eliminated (Nash, 1997). Researchers report that the eliminated connections are not predetermined, as was once thought. Rather, the manner in which a child is raised affects how the brain chooses to wire itself for life (Simmons & Sheehan, 1997).
The concept of "critical periods" for brain development was only a hypothesis prior to a series of innovative experiments conducted in the 1960s and early 1970s. Two researchers, David Hubel and Torsten Wiesel, conducted investigations on how cats' brains were wired for sight. They discovered that by withholding stimuli to a kitten's eyes during a critical period, they blocked the development of connections between the eye and the visual cortex, connections that are necessary for sight. The researchers also discovered that after the critical period had passed, attempts to produce the connections were useless (Begley, 1996; Simmons & Sheehan, 1997). Consequently, according to Dr. Carla Shatz, a neurobiologist at the University of California at Berkeley, "It [the Hubel and Wiesel research discovery] forever changed the way we thought about brain development" (Simmons & Sheehan, 1997, p. 5). Referencing the critical period studies, Sharon Begley (1996) states:
[The studies] suggest that with the right input at the right time, almost anything is possible. But they imply, too, if yo