Male Brains slightly larger than Female Brains [but not proportionately]

Dwight E. Howell deowll at usit.net
Tue Aug 19 22:04:06 EST 1997


A recent article stated that soccer players and perhaps some other
athletes were suffering mini strokes due to getting hit in the head. Men
may need a few more neurons just to get by.

Bart Janssen wrote:

> Of course since there are people who function "normally" with vast
> regions of their brain completely missing, I suspect having a few more
>
> neurons either way makes very little difference.
>
> cheers
> Bart
>
> R. McPherson wrote:
>
> > On Sun, 17 Aug 1997, James Howard wrote:
> >
> > :I started this thread as an example of the effects of testosterone
> on
> >
> > :human brain evolution.
> >
> > :J Comp Neurol 1997 Jul 28;384(2):312-320, "Neocortical neuron
> number
> > in
> > :humans: effect of sex and age." Pakkenberg B, Gundersen HJ
> > :
> > : estimate the total number of neocortical neurons in the
> > :normal human brain
> > : The average numbers of neocortical neurons were 19
> > :billion in female brains and 23 billion in male brains, a 16%
> > :difference.
> > :An
> > :equation predicting the total neocortical neuron number in any
> > :individual in which sex and age are known is provided."
> >
> > I would like to respond to this if I may.
> >
> > The body size to brain size correlation is an inter-specific
> > comparison and is not useful for comparing within a species so it is
>
> > not at all surprising that the study cited above did not find a
> > relationship between human body size and brain size.  A body size to
>
> > brain size correlation can be drawn only when comparing between
> > species of animals.
> >
> > Previous to the study above, neuroscientists have explored potential
>
> > differences between female vs. male brain mass and have concluded
> that
> >
> > while males have larger brains, females have more invagination of
> the
> > cortex.  Thus female brains have essentially the same cortical
> surface
> >
> > area as do male brains.  The cortex in female brains is more folded
> > (invaginated) enabling it to fit into the smaller cranium
> > (smaller body = smaller skull).
> >
> > If the estimation technique used by the above study is legitimate,
> and
> >
> > if the number of samples is sufficient, then perhaps they have
> > identified a characteristic difference in total neocortical neuron
> > numbers.  Before this characteristic is meaningful, we would need to
>
> > be able to establish the 1. distribution of those additional
> neurons,
> > 2. demonstrated activity in those additional neurons, 3. overall
> > differences in neuronal activity during cognitive function in those
> > neurons, and 4 demonstration that more neurons = more function; as
> > opposed to the notion that trimming of neuronal connectivity
> > constitutes refinement of function.  The answer to all of these
> > questions are bound to be sometimes yes and sometimes no and it
> > depends upon which sensory modality is involved and whether you are
> > examining developmental or adult functioning.  So more neurons
> doesn't
> >
> > mean anything right now.
> >
> > I would ask how body size was determined.  If males have a larger
> > somatic body surface, then perhaps more neurons will be required to
> > simply represent more body skin surface (or muscles etc...).  If
> this
> > were true, then more neurons would certainly be expected and would
> not
> >
> > betray any particular propensity for increased cognitive capacity.
> >
> >
> > rjmcpher at uci.edu      Ron McPherson






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