Chapter 3 Puberty and Biological Foundations - The McGraw-Hill ...

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Deprived and Enriched Environments Until the middle of the twentieth century, scientists believed that the brain’s development was determined almost exclusively by genetic factors. Then, researcher Mark Rosenzweig (1969) conducted a classic study. He was curious about whether early experiences can change the brain’s development. He randomly assigned rats and other animals to grow up in different environments. Some lived in an enriched early environment with stimulating features, such as wheels to rotate, steps to climb, levers to press, and toys to manipulate. In contrast, others lived in standard cages or in barren, isolated environments. The results were stunning. The brains of the animals from “enriched” environments weighed more and had thicker layers, more neural connections, and higher levels of neurochemical activity than the brains of the “deprived” animals. Similar findings occurred when older animals were reared in vastly different environments, although the results were not as strong as for younger animals. Researchers have also found depressed activity in children who grow up in unresponsive and unstimulating environments. As figure 3.13 shows, a child who grew up in an impoverished Romanian orphanage had brain activity that was considerably depressed compared with that of a normal child. Can New Brain Cells Be Generated in Adolescence? Until close to the end of the twentieth century, scientists believed that the brain generated no new cells (neurons) after the early child years. However, researchers have recently discovered that people can generate new brain cells throughout their lives (Gould & others, 1999; Kempermann, Wiskott, & Gage, 2004; Lie & others, 2004). Furthermore, evidence now shows that exercise and enriched experiences can produce new brain cells (Churchill & others, 2002; Holmes & others, 2004; Will & others, 2004). Can the Adolescent’s Brain Recover from Injury? In adolescence and even through late adulthood, the brain has a remarkable ability to repair itself (Anderton, 2002; Martino, 2004; Spessot, Plessen, & Peterson, 2004). In chapter 2, you read about Michael Rehbein, whose left hemisphere was removed because of brain seizures. The plasticity of the human brain was apparent as his right hemisphere reorganized itself to take over functions, such as speech, that normally take place in the left hemisphere. While the brain retains considerable plasticity in adolescence, the earlier a brain injury occurs, the more likelihood of a successful recovery (Bhutta & Anand, 2002). One recent study examined 68 children from 7 to 15 years of age and found that the later their brain injuries occurred, the less effective their performance was on a number of language and cognitive tasks (Slomine & others, 2002). Brain Development and Education Numerous claims have been made that elementary and secondary education should be brain-based. Some journalists have even suggested that educators should look to neuroscientists for answers about how best to teach children and adolescents. Unfortunately, such bold statements are speculative at best and far removed from what neuroscientists actually know about the brain (Breur, 1999). We don’t need to look any further than the oversimplified hype about logical “left-brained” individuals and creative “right-brained” individuals to see how easily the relevance of neuroscience to education has been exaggerated (Sousa, 1995). One common misapplication of neuroscience to education is the idea of a critical or sensitive period—a biological window of opportunity—when learning is easy, effective, and readily retained. However, there is no neuroscience evidence to support this belief (Breur, 1999). One leading neuroscientist even told educators that although children acquire a great deal of information during the early years, most learning likely takes place after synaptic formation stabilizes, which is after the age of 10 (Goldman-Rakic, 1996). Keep in mind that we still know very little about brain development in adolescence. In the next decade, we are likely to see many more research studies on brain development in adolescence. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (b) The Brain 81 FIGURE 3.13 Early Deprivation and Brain Activity. These two photographs are PET (positron emission tomography) (which use radioactive tracers to image and analyze blood flow and metabolic activity in the body’s organs) scans of the brains of (a) a normal child and (b) an institutionalized Romanian orphan who experienced substantial deprivation since birth. In PET scans, the highest to lowest brain activity is reflected in the colors of red, yellow, green, blue, and black, respectively. As can be seen, red and yellow show up to a much greater degree in the PET scan of the normal child than the deprived Romanian orphan.
82 Chapter 3 Puberty and Biological Foundations 3 EVOLUTION, HEREDITY, AND ENVIRONMENT 2 Review and Reflect ● LEARNING GOAL 2 Describe the developmental changes in the brain during adolescence Review • What are neurons? How do the brain’s neurons change in adolescence? • What changes in brain structure occur in adolescence? • How much plasticity does the brain have in adolescence? Reflect • Find an article on brain-based education in a magazine or on the Internet. Use your critical thinking skills to evaluate the article’s credibility. Does the author present research evidence to support the link between neuroscience and the brain-based method being recommended? Explain. The Evolutionary Perspective The Genetic Process Heredity-Environment Interaction The size and complexity of the adolescent’s brain emerged over the long course of evolution. Let’s explore the evolutionary perspective on adolescent development and then examine how heredity and environment interact to influence adolescent development. The Evolutionary Perspective Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. In terms of evolutionary time, humans are relative newcomers to the earth. If we think of the broad expanse of time as a calendar year, then humans arrived on Earth in the last moments of December (Sagan, 1977). As our earliest ancestors left the forest to feed on the savannahs, and finally to form hunting societies on the open plains, their minds and behaviors changed. How did this evolution come about? Natural Selection and Adaptive Behavior Natural selection is the evolutionary process that favors those individuals of a species who are best adapted to survive and reproduce. To understand natural selection, let’s return to the middle of the nineteenth century, when the British naturalist Charles Darwin was traveling the world, observing many different species of animals in their natural habitats. In his groundbreaking book, On the Origin of Species (1859), Darwin noted that most species reproduce at rates that would cause enormous increases in their population and yet populations remained nearly constant. He reasoned that an intense struggle for food, water, and resources must occur among the many young born in each generation, because many of them do not survive. Darwin believed that those who do survive to reproduce and pass on their genes to the next generation are probably superior to others in a number of ways. In other words, the survivors are better adapted to their world than the nonsurvivors (Johnson, 2006; Mader, 2004, 2006). Over the course of many generations, Darwin reasoned, organisms with the characteristics needed for survival would compose a larger and larger percentage of the population, producing a gradual modification of the species. If environmental conditions changed, however, other characteristics might be favored by natural selection, moving the evolutionary process in a different direction. To understand the role of evolution in behavior, we need to understand the concept of adaptive behavior (Krogh, 2005; Lewis & others, 2004). In evolutionary conceptions of psychology, adaptive behavior is a modification of behavior that promotes an
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