194 HOW THE BRAIN MAKES POTENTIALvariations.” Using three diff er ent MRI approaches for mea sur ing cortical
thickness and comparing results across two matched samples, the investi-
gators noted “that estimation of CT [cortical thickness] was not consis-
tent across methods,” and “ there was considerable variation in the spatial
pattern of CT- cognition relationships.” And fi nally, “results did not repli-
cate in matched subsamples.”^32
Moreover, functional signifi ca nce is rarely clear, even in simpler brains.
As Cornelia Bargmann and Eve Marder say, describing the connectivity
between all 302 neurons of the roundworm Caenorhabditis elegans was a
stunning success. But it “hides a surprising failure... although we know
what most of the neurons do, we do not know what most of the connections
do... and we cannot easily predict which connections will be impor tant
from the wiring diagram... [and] early guesses about how information
might fl ow through the wiring diagram were largely incorrect.”^33
If we have such diffi culties with 302 neurons, imagine the prob lems
arising from billions of them. Bargmann and Marder suggest that such
unexpected fi ndings, have created doubts about “big science” eff orts to
model connectivity without a better understanding of function.
Th is might explain the results of Hugo Schnack and colleagues, who
found that sometimes (at some ages) thicker cortices are correlated with
IQ. At other times, it is thinner cortices. As they say in their 2015 paper
in Ce re bral Cortex, “Th at intellectual functioning is both associated with
cortical thinning and cortical thickening is puzzling.”^34
Such fl akiness of method could also explain why, in relation to the
roots of intelligence, the results have so far been more hype than real ity.
Although Richard Haier has talked up statistical associations between
such brain mea sures and IQ, as mentioned above, the real ity is more
complex. Following disappointing results in 2009, Haier and colleagues
reported that neural “correlates of the g- factor remain elusive... the sit-
uation with functional imaging studies is no better... suggesting that
identifying a ‘neuro- g’ will be diffi cult.”^35 Th ey also add, somewhat tell-
ingly, that using a “non- theoretically defi ned test may produce confusing
results”— a point I also made earlier in relation to the fruitless gene-
association studies.
Of course, a major assumption driving this research is that brain func-
tions will vary quantitatively across individuals and will be distributed
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