Brain size and IQ 
Author Message
 Brain size and IQ

Warren Searle wrote :


>As I said last Tuesday, there is a correlation of about .35 between
>brain size and IQ among white college freshmen at the U. of Texas in
>Austin, controlling for sex and body size. This result was from a study
>by Lee Willerman using magnetic resonance imaging to measure brain size.
>There is a summary in Science, vol. 245, p. 1584. The study was
>published in _Intelligence_ in spring, 1991, but I don't have the
>specific reference.

The correct issue of Science is Volume 254, page 1584, (13 Dec. 1991).
There is a poorly-labelled graph given there, it is not clear what the
scale for "brain size" plotted in the graph means. The scale extends
from -1.0 to 1.0; and there are no points below about - 0.5 ; the
topmost points are at 1.0.

The sizes plotted are those of 16 slices of the brain as seen by
a magnetic resonance imaging (MRI) machine.  The population was four
groups of ten each : ( male, female ) x (high IQ (>130), low IQ (~100) ).
The average size of equivalent slices of each group is plotted against
slice number.

Whatever the scale means, on the scale that the plot is made it is evident
the difference in brain sizes for high-IQ and low-IQ women is small ( less
than 0.5 ) while for men, the difference is almost 1.5 .

-arun gupta

Thu, 28 Aug 1997 08:50:37 GMT
 Brain size and IQ

The paper that "Science" referred to is  :

Willerman, et. al., "In Vivo Brain Size and Intelligence", Intelligence 15,
223-228 (1991).

Some details :

The sample was 40 right-handed Anglo introductory psychology students,
about 19 years old. These were drawn from a larger pool of introductory
psychology students with SAT scores either >= 1350 or =< 940. "With
prior approval of the University's research review board, students selected
for MRI were required to obtain prorated full-scale IQs of >=130 ( M=136.4,
SD = 3.95) or <= 103 (M=90.5, SD = 8.12), and were equally divided by sex
and IQ classification."

"Using the lowest margin of the cerebellum in a midsagittal view to align
the first axial (horizontal) MR slice", 18 images were taken, each separated
by 2.5mm and 5mm thick. Each image was 256 x 256 pixels with 256 levels of
gray.  Within the boundary of the scalp, all gray scale intensities of < 96
were converted to zero to delete the skull, meninges and interhemispheric
fissure; other brain coverings were deleted manually with a cursor. The
non-zero pixels were then counted, their summed value serving as the index
of overall brain size.

"Brain tissue was present on only 17 of the 18 slices for 12 of the subjects
( 9 women). "

Some peculiarities :

"Average-IQ men were taller than high-IQ men (p < 0.05)."

"After controlling for sex, correlations of height and weight with brain
size were only r = 0.09 and r = 0.10"  (more on why I consider this peculiar
later on.)

Some of the results :

"Among men, IQ scores as a continuous variable correlated with brain size,
before and after adjusting for body size, r = 0.51 (p < 0.05) and r = 0.65
(p< 0.01).  Corresponding correlations for women were r = 0.33 and = 0.35
both n.s."

[does n.s. mean non-significant ? If it does, is there any sense to the
following line : ]

"With sexes pooled, the IQ-adjusted brain-size correlation was r = 0.51
( p<0.1 )"
"This correlation is higher than expected for the general population because
of selection of extreme IQ groups. Applying a statistical correction (Guilford
and Fruchter, 1973) predicted a correlation of r = 0.35 for a more
representative sample."

"Not all brain levels contributed equally to the brain-size-IQ correlation;
[figure 1 : the graph that is displayed in "Science". ]
size differences were greatest for ventricular-level slices in men. These
levels include language circuits, association fibers, and association cortex."


The figure caption :

As mentioned earlier, the average sizes of 16 slices ( labelled from -9,-8,
-7,..., +6) for each of the four groups is plotted on a plot of slice level
vs. brain size standard score that ranges from -1.0 to +1.0.  The largest
differences are between average-IQ and high-IQ males, around slices -3 to +2,
with the high around brain size score 1.0 and the low around brain size
score -0.5.  

The caption reads : Brain area in standard scores ( M = 0 +- SD = 1) by
high versus average IQ and sex, adjusted for weight and height. Squares
refer to men and circles to women, empty symbols refer to high IQ, filled
symbols to average IQ. Slice 0 is at the mid-ventricular level as shown
in the insert [ the insert is a line drawn through a sketch of the brain ]
5 mm thick MRI images are separated by 2.5 mm.  Large brain area -IQ
differences in men near the ventricles (slices -3 below to +1 above 0)
include neural substrates of language and association. A repeated-measures
ANOVA on ventricle size across slices -3 to +1 reveals no effect of sex,
IQ or their interaction (all ps > 0.20) so ventricles are included in area
measurements.  Tissue above or below graphed levels are excluded because all
subjects could not be represented.


  If you take out the ventricular area, isn't the area of brain slice in
the mid-ventricle slices is likely to be much smaller than other brain slices ?
If so, then if the areas of each of the slices are plotted on the same scale,
then these differences will appear to be small relative the sizes of the
other slices, is it not ?  That is, there are large differences in small areas
of the brain -- is that correct ?


Coming to what I mentioned as peculiarities :

(1) "Average-IQ men were taller than high-IQ men (p < 0.05)."

Gould, "The Mismeasure of Man", page 108,

"...Jensen cites an average correlation of 0.25 between IQ and physical
stature" [ Jensen, 1979, "Bias in Mental Testing",pp 361-362].

(2) "After controlling for sex, correlations of height and weight with brain
size were only r = 0.09 and r = 0.10"  

"Analysis of Brain Weight", Ho, et. al., Arch. Pathol. Lab. Med., Vol 104,
Dec. 1980, pages 635, and 640 : finds a correlations of 0.24 and 0.23
(p < 0.01) between body weight and brain weight for white males and females
respectively.  They find  correlations of 0.20 and 0.24 (p<0.01) between body
height and brain weight for white males and white females, respectively.
These numbers are from post-mortem results of people without any obvious
brain pathology.  They also write that "The reported coefficients for
brain weight and body height relationships vary from 0.17 to 0.24 form men
and from 0.09 to 0.23 for women; these are comparable to our results".

[The results vary by race and gender : for example the correlation between
brain weight and

                body height     body weight     body surface area

white  male     0.20 (p<0.01)        0.24 (p<0.01)        0.27 (p<0.05)
black  male     0.20 (p<0.01)        0.15 (p<0.05)        0.20 (p<0.01)
white female    0.24 (p<0.01)   0.23 (p<0.01)     0.29 (p<0.01)
black female    0.15 (p<0.05)   0.10 (p<0.05)   0.14 (p<0.05)

(body surface area in square meteres equals
        (weight in grams)**0.425 x (height in centimeters)**0.725  x 0.007184
(3) Another peculiarity, visible from the graph is that the women have
brain slice areas less than men in the graph; the graph presumably is with
height- and weight-corrected figures. Ho et. al, have "White women have
more brain mass than white men when adjusted for body weight and surface
area, less when adjusted for height."


Finally, from the ISI citation index in the sciences (SCI; SSCI is said to
have more citations), the citations listed for Willerman, et. al., from 91
to May-June 94 are : (of these, Andrease NC is another MRI study like
Willerman , the "Nature" stuff is a debate about P. Rushton; I didn't check
Rushton, Vernon, Jensen or Sells,)

Author          Journal         Vol     page    year
Brand CR        Nature          359     768     92
Rushton JP      Nature          358     532     92
Anderson B      Neurosci L      153     98      93
Andrease NC     Am. J. Psy.     150     130     93 (Psy = Psychiatry)
Heller          J. Affect D     29      129     93
Schultz R       Behav. Genet    23      565     93
Vernon PA       Behav. Genet    23      568     93
Jensen AR       Ann NY Acad     702     103     93
Anderson B      Brain Res       641     160     94
Schultz R       Ann Neurol      35      732     94
Ratcliff        Develop Med     36      533     94
Sells CJ        J Pediat        125     S 9     94


arun gupta

Thu, 28 Aug 1997 10:37:58 GMT
 Brain size and IQ

Some few things :

Sorry for inadvertantly adding an "e" to Warren Sarle's name.
No offense intended.


If there is not a significant correlation between brain size and
IQ for women but there is for men, I personally wouldn't average men
and women to get a population correlation of brain size and IQ.
That may, however, be a matter of taste.  I hope that explains
my comment.


I'm aware that journal space is at a premium and that authors may
be forced to leave out many details that are relevant.


To me to understand or comprehend something is in some part to
build connections with previously acquired information.  If there
are discords, I do not consider myself to have understood. It could
either be that the previous info. is wrong, or the current info. is
wrong, or that I'm building mistaken connections.  Whichever it is
in the case of the Willerman paper, I don't understand some things.


Often, writing on the net causes someone who might know a lot about
these subject in question, but a lurker, to actually write and share
their knowledge.  That is why I consider it useful.

-arun gupta

Fri, 29 Aug 1997 23:33:57 GMT
 Brain size and IQ

My little dog, it a thousand times smarter than my big dogs. Can
elephants do artithemetic, or are they just smart enough not to bother
with it?  Isn't the measure of intelligence rather subjective in itself?  
I think intelligence would be better expresses as a ratio of
             smart things / dumb things
  that a person does in his or her life.


    [1;37;41m       The Amazing TOM LINE!         [0m  
    [1;37;41m -= May The "Flow" Be With You! =-   [0m  

Sat, 30 Aug 1997 03:21:57 GMT
 [ 4 post ] 

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