On the same topic, I just received a copy of an article on sexual differences
in the cortex. Men, it seems, have more neurons in the cortex, but women have
more neuronal processes (braching) per neuron. The reference:

de Courten-Myers, G.M. (1999) The Human Cerebral Cortex: Gender Differences in
Structure and Function. Journal of Neuropathology and Experimental Neurology.
58 (3), 217-226.

de Courten-Myers is an M.D. at the University of Cincinnati Med School (Dept
of Pathoogy and Medicine). A quick glance shows that she integrates her own
work on structural cortical differences with disease data (e.g. dementia) and
psychometric data (cognitive, spatial tasks) and even Kimura's earlier work on
hormones. This is her final paragraph of the paper, followed by the abstract
of the paper:
Conclusion: superimposed on a strong background of functional and structural
equality, human male and female cerebral cortex displays distinct, sexually
dimorphic features and a complex array of gender-specific advanatges and
limitations regarding cognitive functions which are manifest in both health
and disease. "Vive la difference!"
Abstract:  Most people are aware of subtle differences in cognitive functions
between men and women. Psychometric tests confirm specific gender differences
in a number of areas. the most robust being in spatial orientation and
mathematical tasks which are better performed by males. Nonetheless. normal
males and females perform comparably on intelligence tests and
j       human brains lack sexual dimorphism on routine neuropathological exams~ther
than mean differences in weight and size. Even so, human brains demonstrate:
I) a sexually dimorphic nucleus in the hypothalamus with twofold neuronal
numbers in males than infemales; 2) the planum temporale/anterior Sylvian
fissure on the left side are larger in males; 3) some studies reveal the
posterior corpus callosum to be more bulbous in females while others fail to
show this difference; and 4) a cytoarchitectural study demonstrates definite
sexual dimorphism of cerebral cortex with significantly higher neuronal
densities and neuronal number estimates in males and a reciprocal increase in
neuropil/neuronal processes in female cortex as implied by the 2 sexes'
similar mean cortical thicknesses.
Such morphologic differences may provide the structural underpinning for the
gender differences exhibited by the normal and diseased brain. Males manifest
a higher prevalence of mental retardation and of learning disabilities than
females which may reflect the male fetus' smaller overproduction of nerve
cells. Such an inference is supported by the demonstration of 1) better
functional recovery following early brain injury than after later insults, 2)
substantially overproduced and secondarily reduced nerve cells in human
cerebral cortex during gestation, 3) the demonstration of a similar neuronal
production and a testosterone-dependent neuronal involution of the sexually
dimorphic hypothalamic nucleus in rats, and 4) more cortical neurons present
in the adult human male than female. If an overproduced nerve cell population
is capable of compensating for pathologic nerve cell losses taking place
during the process of neuronal involution, the magnitude of overproduced nerve
cells may define the extent of the protection conveyed. Because male fetuses
appear to involute fewer overproduced cortical neurons than females, this
gender difference could explain in part the boys' greater functional
impairments from early brain damage.
Women, on the other hand. exhibit a higher incidence and prevalence of
dementia than do men. Given the females' overall larger extent of cortical
neuropil (neuronal processes) and lower neuronal numbers compared with men,
any disease that causes neuronal loss could be expected to lead to more severe
functional deficits in women due to their loss of more dendritic connections
per neuron lost.
In conclusion, superimposed on a strong background of functional and
structural equality, human male and female cerebral cortex display distinct,
sexually dimorphic features, which can begin to be linked to a complex array
of gender-specific advantages and limitations in cognitive functions.

Ron Blue wrote:
> Gender Gaps on the Brain
> http://abcnews.go.com/sections/science/DyeHard/dye990602.html

* John W. Kulig, Department of Psychology  ************************
* Plymouth State College      Plymouth NH 03264                   *
* [EMAIL PROTECTED]       http://oz.plymouth.edu/~kulig       *
*  "I was made in secret and curiously wrought in the lowest      *
*                parts of the earth" - Psalm 139                  *

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