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attributed to genetics, according to Thompson. But only about 45
percent of the variation in the temporal lobes, which play a central
role in learning and memory, appears to be inherited.
Thompson is now trying to identify specific genes that are
linked to the quality of white matter. The top candidate so far is
a gene for a protein called BDNF, which promotes cell growth.
People with one variation have better-organized fibers, he says.
But environmental factors also play a role. Rodents raised in a
stimulating environment have more white matter. And research
suggests that the apparent IQ di erence between people who were
breast-fed and bottle-fed as babies may arise because breast milk
contains omega-3s, fatty acids involved in the production of myelin;
as a result, some baby formula now includes these compounds.
Hope remains for those who passed the baby-formula stage long
ago. Although the adult brain isn't as malleable as a young brain,
and is therefore less easily influenced by environmental factors,
evidence is growing that the adult brain is still remarkably plastic.
Scientists haven't yet studied white matter enough to know how to
improve it directly, especially in healthy people. But exercise, diet,
and mental activity have all been shown to boost brain health and
decrease the risk of dementia, a disorder that has been linked to
white-matter damage. And other studies have shown that just a few
months of practicing a new skill can enlarge certain parts of the
brain, including parts of the frontal cortex involved in motor plan-
ning and parts of the temporal lobes that integrate visual, auditory,
tactile, and internal physiological information. Similar studies on
ways to improve the quality of white matter are under way.
Although looking at images of my own white matter was fasci-
nating, it was not deeply illuminating. The scan gave me no indi-
cation of how e cient or flexible my mental processes are. And,
the researchers told me, not even the most astute neuroanatomist
would be able to glean a general sense of my cognitive capabilities
from my brain scan.
Learning more about the role of white matter in intelligence
will give scientists a fuller picture of how brain anatomy influences
cognition. It could help explain how di erently structured brains
might produce the same IQ, or whether particular patterns---thick
white matter here, a large chunk of gray matter there---are linked
to particular cognitive strengths and weaknesses. "One of the key
findings that has come out of the last decade of studies of intel-
ligence is the fact that the brain can generate the same IQ score a
number of ways," says Haier. Intelligence is characterized by "indi-
vidual di erences in learning, memory, and attention and how they
are integrated in any one individual." Haier envisions a day when
brain scans could alert teachers to the cognitive strengths and
weaknesses of each student, so that lessons could be individually
tailored. It might be possible to derive much the same information
from extensive cognitive testing, but such testing is rare because
it's expensive and time consuming. A 15-minute brain scan, on the
other hand, might be applied much more broadly.
Although it's not yet possible to estimate someone's IQ from
a brain scan, some scientists say that day may not be far o . "For
a very simple example," says Haier, "suppose the total amount of
gray matter in several areas is a good correlate of IQ, and this cor-
relation gets better if we add additional scan information---perhaps
the amount of white matter in other areas or the amount of activa-
tion in certain areas while a problem is solved. We don't yet know
which combination of brain parameters will be most predictive of
psychometric IQ or other intelligence factors or mental abilities,
but we know how to find out. Once funding is available to scan very
large samples with multiple techniques and test everyone with a
battery of psychometric measures, it's just a matter of time."
That could be a boon for physicians working with Alzheimer's
patients or others su ering from diseases that cause cognitive
damage. Some experts, however, fear it will create the sense that
people's abilities are completely predetermined. Scientists work-
ing in the field argue that using a brain scan to quantify intelligence
is really no di erent from using a standardized test like the SAT.
But because a brain scan measures a physical property, it's likely
to arouse even more concern than today's testing methods. "If you
can estimate someone's IQ from a brain scan, even if it isn't any
more predictive than an SAT [score], it gives the illusion that his
or her future is fixed," says Karama.
In truth, it's not yet clear that brain scans would be any better
than SAT scores at predicting an individual's cognitive function---
or success in school, career, or life. Their value will depend on what
we do with them. Perhaps, as with the SAT, training courses will be
developed to help people improve their scores---to make better use
of the network of connections in their brains. Says UCLA's Frew,
"It's not just the tool. It's how well we are using it."
EMILY SINGER IS TECHNOLOGY REVIEW'S SENIOR EDITOR FOR BIOMEDICINE.
A neuroscientist envisions a day when brain scans could alert
teachers to the cognitive strengths and weaknesses of each
student, so that lessons could be individually tailored.
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