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Physicist, Startup Founder, Blogger, Dad

Thursday, June 23, 2011

What is g?

Neuroscientist John Duncan (FRS, Cambridge) argues that the neurological origin of g is in the frontal and parietal lobes.

Popular science book and public lecture. At 22 minutes Duncan gives a good pragmatic discussion of g in response to an anti-g interlocutor (Howard Gardner disciple). The streaming player at the link doesn't let me skip ahead, so probably better to download the file and play on your machine if you just want to hear this part of the discussion. Best thing to do is get it via iTunes so you can listen to the whole talk at your leisure :-)

A Neural Basis for General Intelligence (Science)

Universal positive correlations between different cognitive tests motivate the concept of “general intelligence” or Spearman's g. Here the neural basis for g is investigated by means of positron emission tomography. Spatial, verbal, and perceptuo-motor tasks with high-g involvement are compared with matched low-g control tasks. In contrast to the common view that g reflects a broad sample of major cognitive functions, high-g tasks do not show diffuse recruitment of multiple brain regions. Instead they are associated with selective recruitment of lateral frontal cortex in one or both hemispheres. Despite very different task content in the three high-g–low-g contrasts, lateral frontal recruitment is markedly similar in each case. Many previous experiments have shown these same frontal regions to be recruited by a broad range of different cognitive demands. The results suggest that “general intelligence” derives from a specific frontal system important in the control of diverse forms of behavior.

The paper above is from 2000. Below is a more recent one, supplied by a commenter. The authors claim a linear model using MRI measurements of brain features (essentially, volumes and activities of particular subregions identified using fMRI) can account for 50% of the variance in g as measured in psychometric tests. Their sample size for the imaging analysis and initial fit of parameters was about 200, and an independent group of 48 was used to test the model.

Multiple Bases of Human Intelligence Revealed by Cortical Thickness and Neural Activation (Journal of Neuroscience)

Choi et al.

We hypothesized that individual differences in intelligence (Spearman’s g) are supported by multiple brain regions, and in particular that fluid (gF) and crystallized ( gC) components of intelligence are related to brain function and structure with a distinct profile of association across brain regions. In 225 healthy young adults scanned with structural and functional magnetic resonance imaging sequences, regions of interest (ROIs) were defined on the basis of a correlation between g and either brain structure or brain function. In these ROIs, gC was more strongly related to structure (cortical thickness) than function, whereas gF was more strongly related to function (blood oxygenation level-dependent signal during reasoning) than structure. We further validated this finding by generating a neurometric prediction model of intelligence quotient (IQ) that explained 50% of variance in IQ in an independent sample. The data compel a nuanced view of the neurobiology of intelligence, providing the most persuasive evidence to date for theories emphasizing multiple distributed brain regions differing in function.


From the conclusions:

... Although our model still does not approach the predictive power of psychometric tests, its high accuracy suggests that neurometric assessments of intelligence may soon become a useful complement to psychometric test. For example, brain images might be used to improve intelligence estimates for individuals whose psychometric scores systematically underestimate their IQ. We hope that future research will build on our neurometric model of intelligence, both refining it so that it generalizes to other populations and expanding it to enhance its accuracy.

Will someone please alert the ghost of Stephen J. Gould concerning dangerous reification activity? I imagine he might still be capable of issuing a fatwa (perhaps via the IMF ;-) despite the fact that this research was conducted in Korea. I'm sure these Koreans and their Yale collaborator are cooking their data just like old George Morton.

20 comments:

MtMoru said...

I could construct a battery where tests of musical ability were the most g-loaded. I'd simply have to make sure most of the subtests tested musical ability.
 
How can it be known that the g-loading of a task isn't simply how well it measures "musical ability", that is, how well it measures the ability which is measured by a majority of tests in the battery?

ben_g said...

g is a good measure of intelligence differences between humans, but I'm not sure it's the same thing that separates our intelligence from other primates.

RKU1 said...

That's interesting about some evidence that g is directly associated with frontal cortex activity.

I've never studied this field and don't really know anything, but I'd always vaguely imagined that g was probably due to something on the purely biochemical level, like the efficiency of neurotransmission or the relaxation-time of neuron firing stimulation or that sort of thing rather than being localized in a specific part of the brain.  I'd partly gotten that idea based on those classic Jensen(?) experiments dealing with response time to light flashes.  On the other hand, I'd thought it was plausible that the secondary principal components of human intelligence---verbal, math, spatial, etc.---might be due to the relative allocation of brain tissue to those slightly different sort of activities, just like dogs allocate so much more of their brains to interpreting smell rather than sight.

botti said...

Some recent papers.
"Based on a review of all the structural and functional neuroimaging literature that was available, Jung and Haier proposed theparieto-frontal integration theory of intelligence (P-FIT), which is arguably the best available description of how intelligence is distributed in the brain."
Based on a review of all the structural and functional neuroimaging literature that was available, Jung and Haier proposed the
parieto-frontal integration theory of intelligence (P-FIT), which is arguably the best available description of how intelligence is distributed in the brain."

http://www.larspenke.eu/pdfs/Deary_Penke_Johnson_2010_-_Neuroscience_of_intelligence_review.pdf

This paper by Choi et al has some nice images.

www.jneurosci.org/content/28/41/10323.full.pdf

Zhengzheng Zhou said...

There is also the theory that "insightfulness" is a little different:


http://brain.oxfordjournals.org/content/128/12/2882.full.pdf+html

Better without (lateral) frontal cortex? Insight problems solved by frontal patients

Carlo Reverberi et al.A recently proposed theory on frontal lobe functions claims that the prefrontal cortex, particularly its dorso-lateral aspect, is crucial in defining a set of responses suitable for a particular task, and biasing these for selection. This activity is carried out for virtually any kind of non-routine tasks, without distinction of content. The aim of this study is to test the prediction of Frith's ‘sculpting the response space’ hypothesis by means of an ‘insight’ problem-solving task, namely the matchstick arithmetic task. Starting from Knoblich et al.'s interpretation for the failure of healthy controls to solve the matchstick problem, and Frith's theory on the role of dorsolateral frontal cortex, we derived the counterintuitive prediction that patients with focal damage to the lateral frontal cortex should perform better than a group of healthy participants on this rather difficult task. We administered the matchstick task to 35 patients (aged 26–65 years) with a single focal brain lesion as determined by a CT or an MRI scan, and to 23 healthy participants (aged 34–62 years). The findings seemed in line with theoretical predictions. While only 43% of healthy participants could solve the most difficult matchstick problems (‘type C’), 82% of lateral frontal patients did so (Fisher's exact test, P < 0.05). In conclusion, the combination of Frith's and Knoblich et al.'s theories was corroborated.

MtMoru said...

"Despite very different task content..."

The subjective judegment which may be the opposite of the truth!

Hao Ye said...

I wouldn't be surprised if there were a number of mechanical factors that are directly associated with g.  I suspect that the psychometric tests that are used to determine g depend on a number of "components" of brain function, including goal-oriented problem solving (as Duncan describes, which many papers have attributed to the frontal cortex) and the transmission speed/efficiency aspect that you describe, but many others as well (possibly related to working memory capacity, recall speed, etc.)

Nano Nymous said...

I assume you are aware of the hilarious dead salmon fMRI results? It would be shocking if g can be reduced to any single factor. "Intelligence" is like "strength" - there are various kinds being controlled by various major factors and affected by a zillion of minor other factors.

MtMoru said...

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reification.

MtMoru said...

"these Koreans and their Yale collaborator are cooking their data"
 
I wouldn't be surprised. 50%? Gould was opposed to the reification of psychometric g. Steve is TOO.

Hao Ye said...

clarification please?  What exactly, have I reified?

If you don't believe g is anything more than a statistical quantity, that's fine: but I don't claim that it is either.  I used the word "associated", but meant it in the statistical sense, and even then, I've phrased everything as hypotheses.

MtMoru said...

That in the same environment some win a Nobel and others clean toilets may be because those who win a Nobel are more suited to that environment.

There are as yet NO biological correlates on mental illness.

Speculating about a physical basis for IQ sounds like astrology.

Hao Ye said...

"That in the same environment some win a Nobel and others clean toilets may be because those who win a Nobel are more suited to that environment."
All aspects of a person at time t are, in some sense, a convolution of that person's innateness (let's say genetics) and environment (SES, exposure to opportunities, epigenetics, etc.)

"The heritability of IQ does not imply that there are absolute qualities of the brain which explain differences in IQ."
The studies Steve described and linked to certainly seem to suggest that there are.  I'm sure there are others.  Do you believe they are all "cooking" their data?

"There are as yet NO biological correlates of mental illness."
I think the research on Schizophrenia alone suggests otherwise.  (unless you think they are all "cooking" their data, too?)

"Speculating about a physical basis for IQ sounds like astrology."
I disagree, there is a big difference between speculation about a mechanism that can be scientifically tested and astrology.  If you don't think so, then you are welcome to ignore my comments, as I ignore horoscopes.

MtMoru said...

"All aspects of a person at time t are, in some sense, a convolution of that person's innateness (let's say genetics) and environment (SES, exposure to opportunities, epigenetics, etc.)."

"The studies Steve described and linked to certainly seem to suggest that there are."

You seem not to understand that what is a good environment for one may not be for another. Change the environment for both and the status of one and the other may be reversed.

"I think the research on Schizophrenia alone suggests otherwise."

You do not know what you are talking about.

"that can be scientifically tested and astrology."

Absolutely true (you don't need the "scientific" modifier). But a physical basis for IQ cannot be tested in the way that a physical basis for eye color can be tested. Eye color doesn't vary with environment. If you've got the genes for blue eyes you'll have blue eyes in every environment. Not true of genes for high IQ. Not true of genes for any psuchological traits. Because the genetic correlates of psychological traits may vary from one man made social material cultural environment to another behavioral gentics like economics is necessarily a pseudoscience. It's "results" depend on time and place.

ben_g said...

Why does variation in environments make it a pseudoscience?  Surely a norm of reaction isn't pseudoscience. And why should the fact that the environment is man-made deter us?  I'm genuinely interested in how much genes vs environments matter for success in our modern society, and in other societies past and present.

Hao Ye said...

"You seem not to understand that what is a good environment for one may be a bad environment for another ..."
"You do not know what you are talking about."
"You also seem not to understand that heritability (...) does not imply a physical basis for schizophrenia in all environments (an absolute physical basis)."
I think it's a bit presumptuous to assume you know what I do or do not understand.  I presented Schizophrenia as an example, because there are many papers on biological correlates (of which you claimed there are none).  Just look at the references under the wikipedia page for it.

"BUT an absolute physical basis for IQ cannot be tested in the way that a physical basis for eye color can be tested. Eye color doesn't vary with environment. If you've got the genes for blue eyes you'll have blue eyes in every environment. Not true of genes for high/low IQ or a particular IQ subtest profile."
1. You are making a claim for which you have failed to present any evidence for.
2. I don't think anyone would reasonable claim that there are genetic determinants for IQ that are as clean cut as they are for eye color.

MtMoru said...

If such and such genes are stronly associated with such and such traits today in the US
different genes may be associated with such and such traits yesterday or in the future in some other place. Man changes his environment as time goes by. Maybe it's just a matter of taste, but when a result is only true temporarily ... how can a science be built on such results?

MtMoru said...

It does seem that way to me Hao. And regarding mental illness I do think you don't know what you're talking about. Although drugs are sometimes helpful in mental illness the reason why is still entirely speculative.

Hao Ye said...

"I don't doubt that there are correlates for the severe mental illnesses, but heritability AND physical correlates doesn't mean genes are causing those correlates."
True, but you didn't say genes initially, you said "There are as yet NO biological correlates of mental illness."  If you meant "genes" when you said "biological correlates", then you should be clearer.

I also agree that IQ is culturally bound, but that doesn't mean that (1) biological mechanisms don't explain part of the variance in IQ, nor that (2) such hypothetical mechanisms aren't genetically determined, to some extent. 

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