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.
> R. McPherson wrote:
> > On Sun, 17 Aug 1997, James Howard wrote:
> > :I started this thread as an example of the effects of testosterone
> > :human brain evolution.
> > :J Comp Neurol 1997 Jul 28;384(2):312-320, "Neocortical neuron
> > 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
> > while males have larger brains, females have more invagination of
> > cortex. Thus female brains have essentially the same cortical
> > 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,
> > 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
> > 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
> > 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
> > were true, then more neurons would certainly be expected and would
> > betray any particular propensity for increased cognitive capacity.
> > rjmcpher at uci.edu Ron McPherson
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