Study Finds Genetic Link Between Intelligence and Size of Some Regions of the
By NICHOLAS WADE
Plunging into the roiled waters of human intelligence and its heritability,
brain scientists say they have found that the size of certain regions of the
brain is under tight genetic control and that the larger these regions are the
higher is intelligence.
The finding is true only on average and cannot be used to assess an
individual's intelligence, said Dr. Paul M. Thompson, the leader of the
research team and a pioneer in mapping the structure of the brain.
The measurement of intelligence has long been a controversial issue, and even
more so the efforts to tease out the relative contributions of heredity and
Dr. Bruce L. Miller, a neurologist at the University of California at San
Francisco and an expert on brain changes in Alzheimer's disease, said Dr.
Thompson's work was "an exciting study that starts to show there are some
brain areas in which there are very significant genetic influences on
And Dr. Robert Plomin, a psychologist who studies intelligence at the
Institute of Psychiatry in London, said the high correlation found between the
size of certain areas of the brain and general intelligence "does make it
harder to dismiss intelligence as some meaningless construct, as some want to
Dr. Thompson, who is at the University of California at Los Angeles, uses a
type of brain scanning called magnetic resonance imaging, which can show the
difference between gray matter and white matter in the living brain. The gray
matter consists of brain cells, while the white matter comprises the bundles
of wiring with which the cells communicate with one another. The amount of
gray matter is a measure of the number of brain cells.
The human brain seems to be divided into modules that perform separate tasks.
The frontal lobes are involved in planning and risk assessment, while regions
at the back of the brain handle visual processing. Dr. Thompson has tried to
discover if the relative size of the brain's modules is under genetic control
by studying how their size varies in twins.
With the help of colleagues in Finland, where a national registry of twins is
maintained, he scanned the brains of identical and fraternal pairs of twins
and measured the size of the brain modules. Qualities that are under genetic
control show a characteristic pattern of varying hardly at all between
identical twins, who have the same genes; quite a lot between fraternal twins,
who share about half their genes; and a great deal between unrelated
The researchers had their computer draw three-dimensional maps of each
subject's brain, and then color coded the modules' degree of heritability. In
an article published in today's issue of Nature Neuroscience, they report that
the quantity of gray matter in the frontal lobes was under particularly tight
genetic control, as was a region at the side of the left hemisphere known as
Wernicke's area, which is central to language.
Dr. Thompson's reason for probing the genetic control of brain structure was
to uncover genes that might be involved in mental diseases that can be
inherited, like schizophrenia and autism. But he and his colleagues also
wished to understand the role of brain modules in healthy individuals, so they
gave their subjects intelligence tests and found that intelligence was
significantly linked with the amount of gray matter in the subjects' frontal
Dr. Thompson said the findings were "the first maps of the degree to which the
genes control brain structure." There were only 40 subjects in his study — 10
pairs of identical twins and 10 pairs of fraternal twins — but the results
gave "enough statistical power to identify the key brain systems," he said.
He expressed surprise that the amount of gray matter in the frontal lobes
turned out to be correlated with intelligence in his study "because you
wouldn't think something as simple as gray matter would affect something as
complicated as intelligence." But the amount of gray matter, which is related
to the number of brain cells, perhaps reflects something that bears more
directly on intelligence, like the number of cell- to-cell connections, he
Dr. Plomin, who wrote a commentary on the study in the journal, said the
larger volume of gray matter could be the cause of higher intelligence, or it
could be the other way around — people with a stronger motivation, say, might
exercise their brains harder and develop a higher density of neurons.
As brain-scanning studies like Dr. Thompson's become more refined, they raise
the possibility that a scan could be used to gauge various elements of
personality or behavior.
Dr. Thompson said he believed that as brain scans become increasingly
informative they will raise issues of personal privacy just as genetic testing
has done, and should be protected with similar safeguards.
The size of gray matter in the frontal lobes cannot be used to measure an
individual's intelligence, he said. Some potential uses, such as scanning to
compare the intelligence of different groups, would be unethical, he added.
"It would be remiss to use technology developed for disease for those types of
goals," he said.
--- --- --- --- ---
Useless hypotheses, etc.:
consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism, GAC, Cyc, Eliza, cryonics, individual
uniqueness, ego, human values, scientific relinquishment, malevolent AI
We move into a better future in proportion as science displaces superstition.
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