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

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.
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(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.