Which plays a more important role in brain development, nature (genes) or nurture (environment)?
Genes and environment interact at every step of brain development, but they play very different roles. Generally speaking, genes are responsible for the basic wiring plan—for forming all of the cells (neurons) and general connections between different brain regions--while experience is responsible for fine-tuning those connections, helping each child adapt to the particular environment (geographical, cultural, family, school, peer-group) to which he belongs. An analogy that is often used is wiring a phone network: genes would specify the number of phones and the major trunk lines that connect one relay station to the next. Experience would specify the finer branches of this network-the connections between the relay station and each person's home or office.
For example, each of us is born with the potential to learn language. Our brains are programmed to recognize human speech, to discriminate subtle differences between individual speech sounds, to put words and meaning together, and to pick up the grammatical rules for ordering words in sentences. However, the particular language each child masters, the size of his vocabulary, and the exact dialect and accent with which he speaks are determined by the social environment in which he is raised--that is, the thousands of hours he has spent (beginning even before birth) listening and speaking to others. Genetic potential is necessary, but DNA alone cannot teach a child to talk.
Does experience change the actual structure of the brain?
Yes. Brain development is "activity-dependent," meaning that the electrical activity in every circuit—sensory, motor, emotional, cognitive--shapes the way that circuit gets put together. Like computer circuits, neural circuits process information through the flow of electricity. Unlike computer circuits, however, the circuits in our brains are not fixed structures. Every experience--whether it is seeing one's first rainbow, riding a bicycle, reading a book, sharing a joke--excites certain neural circuits and leaves others inactive. Those that are consistently turned on over time will be strengthened, while those that are rarely excited may be dropped away. Or, as neuroscientists sometimes say, "Cells that fire together, wire together." The elimination of unused neural circuits, also referred to as "pruning," may sound harsh, but it is generally a good thing. It streamlines children's neural processing, making the remaining circuits work more quickly and efficiently. Without synaptic pruning, children wouldn't be able to walk, talk, or even see properly.
What is a "critical period" in brain development?
Pruning or selection of active neural circuits takes place throughout life, but is far more common in early childhood. Animal studies have shown that there are certain windows of time during which the young are especially sensitive to their environment: newborn mice must experience normal whisker sensation in the first few days of life or they will develop abnormal tactile sensitivity in the face region; cats must be allowed normal visual input during the first three months or their vision will be permanently impaired; and monkeys need consistent social contact during the first six months or they will end up extremely emotionally disturbed. Many of the same critical periods appear to hold for human development, although we are less certain about their exact length. Thus, babies also require normal visual input or they may suffer permanent impairment; children born with crossed or "lazy" eyes will fail to develop full acuity and depth perception if the problem is not promptly corrected. Language skills depend critically on verbal input (or sign language, for babies with hearing impairments) in the first few years or certain skills, particularly grammar and pronunciation, may be permanently impacted. The critical period for language-learning begins to close around five years of age and ends around puberty. This is why individuals who learn a new language after puberty almost always speak it with a foreign accent.
Are there critical periods in the development of every brain function?
Probably not. In the case of visual development, certain abilities are more at-risk than others when a young child's vision is impaired by eye-crossing or other visual problems (such as congenital cataracts). Thus, two visual abilities--acuity (the perception of fine detail) and binocularity (the coordinated use of both eyes), which is especially important for depth perception--do depend on normal visual experience as a child, whereas two other visual abilities--color and peripheral vision--are not impaired by visual problems in early life. A similar distinction holds for language development: certain skills (including grammar and phonology--the ability to perceive and produce individual speech sounds) are more sensitive than others (such as vocabulary size) to a child's experience with language in the first few years of life.
We know much less about the development of other mental skills, such as emotional functioning, mathematical ability, or musical skill. If their development is comparable to vision and language, we may expect that some features will be subject to a critical period while others are not. One musical skill known as "perfect pitch"--the ability to identify a musical note without reference to a tuning note--seems to develop only in musicians who began their training before the age of seven (and then, not in all professional musicians). Similarly, a child's social-emotional development depends on a positive, nurturing attachment to a primary caregiver, based on the higher frequency of serious behavioral problems among children who were severely neglected during the first year or more of life, (such as the thousands of Romanian children reared in state-run orphanages). Comparable problems emerge among monkeys who are reared in isolation, and neuroscientists are beginning to understand how the lack of attachment in infancy alters development of emotional areas of the primate brain.
Why does the developing brain undergo these critical periods in its development?
Neuroscientists do not yet fully understand the biological basis of these critical periods. One theory is that they correspond to a period of synaptic excess in the brain: between infancy and the early grade school years, the brain actually over-produces connections--some 50 percent more than will be preserved in adulthood. During the critical period, a child's experience--sensory, motor, emotional, and intellectual--determines which of these synapses will be preserved, through pruning of the least useful connections. In this way, each child's brain becomes better tuned to meet the challenges of his or her particular environment.
A related theory holds that learning itself creates critical periods in a child's brain. That is, the longer a child has been exposed to one type of experience or environment, the less likely he or she will be able to reverse the synaptic learning that has already taken place. Animal studies provide some support for this theory. For example, kittens that are deprived of all vision (as opposed to the vision in just one eye) in the first few months of life show a delayed critical period for visual experience, beginning from the time their deprivation ends. Similarly, songbirds normally learn their species-typical songs early in life, by listening to adults of the same species. However, when newly hatched birds of certain species are isolated, permitting them no song exposure during early life, their critical period for song learning is delayed, even as late as adulthood.
5Likes
LinkBack URL
About LinkBacks
Originally Posted by dan hunter
I was wondering if the guy himself would truly believe he is GOD. Especially if he did not have any kind of interaction with anything other than his own being. I am not even sure he would recognize he had a body.
