perplexed in peoria

Editor's Summary
Nature - 30 March 2006

Here's a subject guaranteed to cause controversy: the
relationship between intelligence, measured by IQ tests,
and physical brain development in children and adolescents.
A study that followed 307 typically developing subjects
from childhood to adolescence (roughly between the ages of
6 and 19 years) now suggests that 'brainy' children are not
cleverer by virtue of having more or less grey matter at
any one age. Rather, intelligence is related to various
aspects of the continuing process of cortical maturation.
Specifically, the trajectory of change in the thickness of
the cerebral cortex, not cortical thickness itself, relates
to intelligence. More intelligent children demonstrate a
particularly plastic cortex, with an initial accelerated
and prolonged phase of cortical increase, which yields
to equally vigorous cortical thinning by early adolescence.
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News and Views
X-Ray imaging: Soft focus
Ed Gerstner
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Letter
Intellectual ability and cortical development in children and adolescents
P. Shaw, et al.
Nature 440, 676-679 (30 March 2006)

First paragraph: Children who are adept at any one of the
three academic 'R's (reading, writing and arithmetic) tend
to be good at the others, and grow into adults who are
similarly skilled at diverse intellectually demanding
activities. Determining the neuroanatomical correlates
of this relatively stable individual trait of general
intelligence has proved difficult, particularly in the
rapidly developing brains of children and adolescents.
Here we demonstrate that the trajectory of change in the
thickness of the cerebral cortex, rather than cortical
thickness itself, is most closely related to level of
intelligence. Using a longitudinal design, we find a
marked developmental shift from a predominantly negative
correlation between intelligence and cortical thickness
in early childhood to a positive correlation in late
childhood and beyond. Additionally, level of intelligence
is associated with the trajectory of cortical development,
primarily in frontal regions implicated in the maturation
of intelligent activity. More intelligent children
demonstrate a particularly plastic cortex, with an initial
accelerated and prolonged phase of cortical increase, which
yields to equally vigorous cortical thinning by early
adolescence. This study indicates that the neuroanatomical
expression of intelligence in children is dynamic.
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My comment: 'Guaranteed to cause controversy' only because
some people believe that the phenomenon being studied (IQ)
doesn't exist, and if it does exist, should not be studied.

dk

Until those people come up with some viable alternative, they
can bitch and moan all they want. Everyone understands IQ is
a crude measure. But it's the best we've got for now.

DK

william morse

There was a discussion of this result on NPR today. One thing noted was
that it is not clear how much of the changes in development are due to
genetics and how much are due to environment.


No that's not the only reason. The other side of the coin is that some
people use differences in IQ as an excuse for racism, and in doing so
have consistently confused heritability as a measurement with the concept
of genetic determinism. Height is clearly heritable - but if your mother
is tall, and your father is tall, and you are undernourished you will
still be short, even though you will be taller than a similarly
undernourished person whose mother and father were short.

And the third side of the coin - dang it's hard to make choices with
these three sided coins :-) - is the rather strange attitude of modern
society towards high perceived intelligence. High perceived intelligence
is clearly a very mixed blessing if you are female. High perceived
intelligence is a much more positive trait if you are male - except if it
is too high, in which case you are a geek, except if you go to an Ivy
League (or equivalent) college, in which case you are a success story.


Yours,

Bill Morse

ekurtz99

One hears this complaint again and again; do you have a recent
reference to someone actually saying or writing it?
The usual evidence cited in support of the hereditarian view of IQ is
the correlation of the IQs of MZ twins separated at birth and given up
for adoption into different families - most studies show a cc of ~ 0.78.

[moderator's note: I'd be interested in seeing references for this
claim; my recollection is that such numbers are actually r values,
not the actual correlation coefficient, which is r^2. - JAH]

ekurtz99

It actually depends on the context; if the issue is differences between
racial groups, IQ is a wicked racist tool; when it comes to getting
low-IQ murderers off death row, it is an infallible measure of
cognitive ability. For those who get a high score, it accurately
reflects their innate ability; for low-scorers, it is a set of prosaic
and irrelevant question that cannot hope to capture the essence of
their unique intellects.

perplexed in peoria

I grant you all three sides of your coin. The relationship between
IQ and race, heredity, environment, and ability to get a date is,
and should be, controversial. But if the relationship between IQ
and the brain is controversial, then either the controversialist
believes that IQ is an attribute of the soul (not the brain), or
believes that IQ doesn't exist, or just gets upset when the subject
of IQ is even mentioned.

whitesickle

Well, this study is possibly good news. We'll be able to test them
early and find out which ones are intelligent and which ones are less
intelligent and place them in the appropriate classes. I think this
study is potentially controversial because of the important the
environment plays in cortical plasticity and IQ is just incidental
here. The study states, "Using a longitudinal design, we find a marked
developmental shift from a predominantly negative correlation between
intelligence and cortical thickness in early childhood to a positive
correlation in late childhood and beyond. Additionally, level of
intelligence is associated with the trajectory of cortical development,
primarily in frontal regions implicated in the maturation of
intelligent activity." The inference here is that the level of
intelligence associated with the trajectory of cortical development,
primarily in frontal regions implicated in the maturation of
intelligent activity is linked to a marked developmental shift from a
predominantly negative correlation in late childhood to a positive
correlation in late childhood and beyond. But the abstract doesn't
highlight specifically the IQ differences between early childhood to
childhood and adolescence. It merely states, "More intelligent children
demonstrate a particularly plastic cortex, with an intial and prolonged
phase of cortical increase, which yields to equally vigorous cortical
thinning by adolescence." So we can assume throughout early childhood,
childhood, and adolescence cortex development in children with higher
IQs exhibit these factors. It would be interesting to know which
children and adolescents scored higher IQs. Generally, adolescents
would apparently score the highest but there may have been a few early
age children and middle aged children who had just as high scores as
the highest scoring adolescent. I wonder if the authors of this study
broke down the populations into groups such as early aged children,
middle aged children, and adolescents and gave the averages in terms of
cortical development/plasticity and comparing it to IQ. The study
answers this by stating, "More intelligent children
demonstrate a particularly plastic cortex, with an initial accelerated
and prolonged phase of cortical increase, which yields to equally
vigorous cortical thinning by early
adolescence. This study indicates that the neuroanatomical expression
of intelligence in children is dynamic."

Jim writes, "Here is a study that followed 307 typically developing
subjects
from childhood to adolescence (roughly between the ages of
6 and 19 years)." As the study states, "Determining the neuroanatomical
correlates
of this relatively stable individual trait of general intelligence has
proved difficult, particularly in the rapidly developing brains of
children and adolescents." The researchers seemed to wisely stay clear
of heriditarian-environmental conclusions. Nevertheless, it is more
likely the environment will have more of a physiological role on the
developing brain of a six year old child and an adolescent than on an
adult. Furthermore, this environment starts as early as in utero. We
are a product of both are genes and the environment and it is likely
impossible at present to know how much IQ tests of these children are a
mixture of the two.

The study did its job and the reason I'm mentioning the aforementioned
is that it is possible some scientists will clasp on to it as further
"genetic" evidence "intelligence" is hardwired and that more
intelligent children demonstrate a particularly plastic cortex, with an
initial accelerated and prolonged phase of cortical increase, which
yields to equally vigorous cortical thinning by early adolescence.
Afterall, if the researchers in this study could make such
determinations of who is and isn't "intelligent" based on
neuroanatomical correlates then theoretically such a screening and
testing program could be done. Would that be a good idea? Not unless we
scientifically know for sure what intelligence is.

Michael Ragland

william morse

Phillipe Rushton springs to mind. I just recently deleted links to a few
of his articles because it had been a while since the subject came up. I
don't really want to have to reread his tripe to give you specifics.

Did any of those studies use MZ twins separated immediately after
splitting and separately brought to term, one in an impoverished mother
and one in a pampered mother? With one of them black, raised in an
innercity environment by a single parent household, while the other was
white, raised in a white upperclass neighborhood? Come back to me with
that study and we can talk about correlation coefficients.

Now the adopted vs. natural children comparisons answer some of these
questions - but they still leave out developmental effects in the womb
and the effects of racial stigma independent of parental race.

This is not to deny that intelligence is inherited (although there is
room for debate in how well it is measured by IQ tests). Everyone knows
this - in fact (as long as we are being controversial), it is a
significant factor in mating decisions among humans. Humans mate
assortatively, and intelligence is one factor used in the ranking.
Perhaps this is simply that humans recognize that too great a difference
in intelligence is likely to lead to an unhappy marriage. But
interestingly, when asked about relationships after only a short period
of time together, women are more willing to engage in them if the male is
"much smarter than average". The obvious conclusion is that intelligence
is a trait that is recognizable, desirable, and heritable.

Yours,

Bill Morse

perplexed in peoria

Are you sure about this, Josh? The texts I have consulted use 'r'
as the symbol for the correlation coefficient itself. The value r^2
represents the fraction of the variance in the dependent variable that
is 'explained' by variance in the independent variable.

So, if MZ twins adopted separately have a correlation coefficient
r = 0.707, then r^2 is roughly 0.5 and half of the variance in IQ
is caused by something other than genetics - presumably a large
part of it by differences in the environments between the two twins.

perplexed in peoria

You are discussing subjective assessments of intelligence, based
on 'a short period of time together'. While I am sure that such
assessments are correlated with measured IQ, I wonder how well
correlated. And I wonder which of the two 'measures' of 'intelligence'
correlates better with job success and/or academic success.

It would also be interesting to know something about the outliers -
persons who make a good first impression regarding intelligence but
just don't do well on the tests. And vise-versa. I suspect that
the women you mention are basing their evaluation mostly on verbal
skills. I doubt that they attach much weight to ability to perform
mental rotations of three dimensional objects. And, for some reason,
they are negatively impressed with ability to navigate without asking
for directions!