“And the male is not like the female”(V.3:36).

The brain is male or female
That men and women are different, everyone knows that. But, aside from external anatomical and primary and secondary sexual differences, scientists know also that there are many other subtle differences in the way the brains from men and women process language, information, emotion, cognition, etc. One of the most interesting differences appear in the way men and women estimate time, judge speed of things, carry out mental mathematical calculations, orient in space and visualize objects in three dimensions, etc. In all these tasks, women and men are strikingly different, as they are too in the way their brains process language. This may account, scientists say, for the fact that there are many more male mathematicians, airplane pilots, bush guides, mechanical engineers, architects and race car drivers than female ones.
On the other hand, women are better than men in human relations, recognizing emotional overtones in others and in language, emotional and artistic expressiveness, esthetic appreciation, verbal language and carrying out detailed and pre-planned tasks. For example, women generally can recall lists of words or paragraphs of **** better than men (13).
Hormones that are present during a baby's development will affect the brain and determine whether the brain will be female or male. Studies that have looked at differences in the brains of males and females have focused on:
1. Total Brain Size
2. The Corpus Callosum
3.The Hypothalamus

Differences in Total Brain Size?
Almost all studies show that at birth, a boy's brain is bigger than a girl's brain. At birth, the average brain of boys is between 12-20% larger than that of girls. The head circumference of boys is also larger (2%) than that of girls. However, when the size of the brain is compared to body weight at this age, there is almost no difference between boys and girls. So, a girl baby and a boy baby who weigh the same will have similar brain sizes.
In adults, the average brain weight in men is about 11-12% MORE than the average brain weight in women. Men's heads are also about 2% bigger than women's. Remember though, men on average weigh more than women and that absolute brain size may not be the best measure of intelligence. Many behavioral differences have been reported for men and women. For example, it has been said that women are better in certain language abilities and men are better in certain spatial abilities. Brain Weights

(Data from Dekaban, A.S. and Sadowsky, D., Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights, Ann. Neurology, 4:345-356, 1978)
Differences in the Corpus Callosum?
The major pathway that connects the right and left cerebral hemispheres is called the corpus callosum. (The corpus callosum is the fiber tract made up of 200-250 million axons that is cut in split brain patients.) Some claims have been made that the corpus callosum is bigger and more developed in women than in men. These claims have even been reported in the popular media (Time Magazine, Jan. 20, 1992, pp. 36-42; Newsweek Magazine, March 27, 1995, pp. 51). In layman's terms, it means that the two sides of the female brain "talk" better to each other -- which could explain why studies show women tend to multi to multi-task better.

Differences in the Hypothalamus?
The hypothalamus is one area of the brain with well-********ed differences between men and women. Two areas of the hypothalamus, the preoptic area and the suprachiasmatic nucleus, have clear differences in female and male brains.
Preoptic Area of the Hypothalamus
This area of the hypothalamus is involved in mating behavior. In males of several species including humans, the preoptic area is greater in volume, in cross-sectional area and in the number of cells. In men, this area is about 2.2 times larger than in women and contains 2 times more cells. Apparently, the difference in this area is only apparent after a person is 4 years old. At 4 years of age, there is a decrease in the number of cells in this nucleus in girls. The exact function of this nucleus in behavior is not fully known.
Suprachiasmatic Nucleus of the Hypothalamus
This area of the hypothalamus is involved with circadian rhythms and reproduction cycles. The only difference between women and men in this area is one of shape: in males, this nucleus is shaped like a sphere; in females it is more elongated. However, the number of cells and volume of this nucleus are not different in men and women. It is possible that the shape of the suprachiasmatic nucleus influences the connections that this area makes with other areas of the brain, especially the other areas of the hypothalamus.

Brain size
In 1861, Paul Broca examined 432 human brains and found that the brains of males had an average weight of 1325 grams, while the brains of females had an average weight of 1144 grams. A 1992 study of 6325 Army personnel found that men's brains had an average volume of 1442 cm³, while the women averaged 1332 cm³. (Ankney 1992[8]). The differences are smaller but persist when adjusted for body size (Ankey, 1992).

Side view of male and female human brains
In 2005, Haier et al. reported that compared with men, women show more white matter and fewer gray matter areas related to intelligence. They also report that the brain areas correlated with IQ differ between the sexes. They conclude that men and women apparently achieve similar IQ results with different brain regions. [9]
Although women may have smaller brains than men, they appear to have greater neuron density in their prefrontal lobe ([10]), which is involved in higher functions such as planning, judgement, and language, although men still have higher absolute grey matter volume than women in their prefrontal lobe ([11]).
• Born, M. P., Bleichrodt, N. & van der Flier, H. (1987). "Cross-cultural comparison of sex-related differences on intelligence tests". Journal of Cross-Cultural Psychology 18: 283–314.
• Geary, D. (1998). Male, female: The evolution of human sex differences. Washington, DC: American Psychological Association.
• Haier RJ, Benbow CP. (1995). "Sex differences and lateralization in temporal lobe glucose ****bolism during mathematical reasoning". Dev Neuropsychol. 11: 405–414.
• Haier RJ, Jung RE, Yeo RA, et al. (2005). "The neuroanatomy of general intelligence: sex matters". NeuroImage 25: 320–327.
• Lynn, Richard, with P.Irwing and T.Cammock (2002). "Sex differences in general knowledge". Intelligence 30: 27–40.
• Lynn, Richard (1999). "Sex differences in intelligence and brain size: a developmental theory". Intelligence 27: 1–12.
• Stumpf, H. and Jackson, D. N. (1994). "Gender-related differences in cognitive abilities: evidence from a medical school admissions program". Personality and Individual Differences 17: 335–344.
• IJ Deary, G Thorpe, V Wilson, JM Starr, LJ Whalley (2003). "Population sex differences in IQ at age 11: the Scottish mental survey 1932". Intelligence 31: 533–542.
• Larry V. Hedges; Amy Nowell (1995). "Sex Differences in Mental Test Scores, Variability, and Numbers of High-Scoring Individuals". Science 269: 41-45.
• Nyborg, Helmuth (2005). "Sex-related differences in general intelligence g, brain size, and social status". Personality and Individual Differences 39: 497-509.
1. ^ Paul Irwing, Richard Lynn, "Sex differences in means and variability on the progressive matrices in university students: a ****-analysis," British Journal of Psychology, 96(4):505-524, 2005 November.
2. ^ BBC reporting Lynn & Irwing study, 2005
3. ^ Guardian reporting Lynn & Irwing study and Blinkhorn's reply, 2005
4. ^ Blinkhorn, S. Intelligence: a gender bender, Nature 2005 Nov 3;438(7064):31-2.
5. ^ Original Boston Globe story reporting the remarks of Larry Summers at a January 2005 conference
6. ^ Tran****** of Summers' remarks at NBER Conference on Diversifying the Science & Engineering Workforce
7. ^ Summers' initial response to controversy
8. ^ University Will Commit $50M to Women in Science, Harvard Crimson, 2005 May 16
9. ^ Barres, Ben (13 July 2006). Does Gender Matter? Nature
[edit] External links
• Pinker vs. Spelke, The Science of Gender and Science
• Sex Differences in the Brain, by Doreen Kimura, Scientific American
• Summerstime, and the living ain't easy: Free speech and academia, The Economist Feb 24th 2005
• "Be a man: Men compete harder than women. That is why they do better at work", The Economist Jun 26th 2003
• Men and Women Achieve Intelligence Differently, by Janis Kelley, NeuroPsychiatry Reviews
• "Is this a clever thing to say about women's IQ?"
• Various medline abstracts
• Website of Doreen Kimura, contains links to more papers on subject
o "Sex, sexual orientation and sex hormones influence human cognitive function"
• Sex Differences in Brain Gray and White Matter in Healthy Young Adults: Correlations with Cognitive Performance

Scientists working at Johns Hopkins University, recently reporting in the "Cerebral Cortex" scholarly journal (1), have discovered that there is a brain region in the cortex, called inferior-parietal lobule (IPL) which is significantly larger in men than in women. This area is bilateral and is located just above the level of the ears (parietal cortex). This is the same area which was shown to be larger in the brain of Albert Einstein, as well as in other physicists and mathematicians. So, it seems that IPL's size correlates highly with mental mathematical abilities
The study, led by Dr. Godfrey Pearlson, was performed by analyzing the MRI scans of 15 men and women. After allowing for the natural differences in overall brain volume which exist between the brains of men and women, there was still a difference of 5% between the IPL volumes (human male brains are, on average, approximately 10 % larger than female, but this is because of men's larger body size: more muscle cells imply more neurons to control them).
Another previous study by the same group led by Dr. Godfrey Pearlson (9) has shown that two areas in the frontal and temporal lobes related to language (the areas of Broca and Wernicke, named after their discoverers) were significantly larger in women, thus providing a biological reason for women's notorious superiority in language-associated thoughts. Using magnetic resonance imaging, the scientists measured gray matter volumes in several cortical regions in 17 women and 43 men.
Women had 23% (in Broca's area, in the dorsolateral prefrontal cortex) and 13% (in Wernicke's area, in the superior temporal cortex) more volume than men.
In another research, a group from the University of Cincinnati, USA, Canada, presented morphological evidence that while men have more neurons in the cerebral cortex, women have a more developed neuropil, or the space between cell bodies, which contains synapses, dendrites and axons, and allows for communication among neurons (8). According to Dr. Gabrielle de Courten-Myers, this research may explain why women are more prone to dementia (such as Alzheimer's disease) than men, because although both may lose the same number of neurons due to the disease, "in males, the functional reserve may be greater as a larger number of nerve cells are present, which could prevent some of the functional losses."
Fact and Prejudice
But do these differences mean a superiority/inferiority relationship between men and women?
"No", says Dr. Pearlson. "To say this means that men are automatically better at some things than women is a simplification. It's easy to find women who are fantastic at math and physics and men who excel in language skills. Only when we look at very large populations and look for slight but significant trends do we see the generalizations. There are plenty of exceptions, but there's also a grain of truth, revealed through the brain structure, that we think underlies some of the ways people characterize the sexes."
The conclusion is that neuroscience has made great strides in the 90s, regarding the discovery of concrete, scientifically proved anatomical and functional differences between the brains of males and females. While this knowledge could in theory be used to justify prejudice against women, fortunately this has not happened. In fact, this new knowledge may help physicians and scientists to discover new ways to explore the brain differences in the benefit of the treatment of diseases, the personalized action of drugs, different procedures in surgeries, etc. After all, males and females differ only by one Y chromosome, but this makes a real impact upon the way we react to so many things, including pain, hormones, etc.
To Know More
Sabbatini, R.M.E.: The PET Scan: A New Window Into the Brain
Gattass, R.: Thoughts: Image Mapping by Functional Nuclear Magnetic Resonance
Cardoso, S.H.: Why Einstein Was a Genius?
Sabbatini, R.M.E.: Paul Broca: Brief Biography
Sabbatini, R.M.E.: Mapping the Brain
1. Frederikse, M.E., Lu, A., Aylward, E., Barta, P., Pearlson, G. Sex differences in the inferior parietal lobule. Cerebral Cortex vol 9 (8) p896 - 901, 1999 [MEDLINE].
2. Geary, D.C. Chapter 8: Sex differences in brain and cognition. In "Male, Female: the Evolution of Human Sex Differences". American Psychological Association Books. ISBN: 1-55798-527-8 [AMAZON].
3. Harasty J., Double K.L., Halliday, G.M., Kril, J.J., and McRitchie, D.A. Language-associated cortical regions are proportionally larger in the female brain. Archives in Neurology vol 54 (2) 171-6, 1997 [MEDLINE].
4. Collaer, M.L. and Hines, M. Human behavioural sex differences: a role for gonadal hormones during early development? Psychological Bulletin vol 118 (1): 55-77, 1995 [MEDLINE].
5. Bishop K.M. and Wahlsten, D. Sex differences in the human corpus callosum: myth or reality? Neuroscience and Biobehavioural Reviews vol 21 (5) 581 - 601, 1997.
6. LeVay S. A difference in hypothalamic structure between heterosexual and homosexual men Science. 253(5023):1034-7, 1991 [MEDLINE].
See also: LeVay, S.: "The Sexual Brain". MIT Press, 1994 [AMAZON]
7. Shaywitz, B.A., et al. Sex differences in the functional organisation of the brain for language. Nature vol 373 (6515) 607 - 9, 1995 [MEDLINE].
8. Rabinowicz T., Dean D.E., Petetot J.M., de Courten-Myers G.M. Gender differences in the human cerebral cortex: more neurons in males; more processes in females. J Child Neurol. 1999 Feb;14(2):98-107. [MEDLINE]
9. Schlaepfer T.E., Harris G.J., Tien A.Y., Peng L., Lee S., Pearlson G.D. Structural differences in the cerebral cortex of healthy female and male subjects: a magnetic resonance imaging study. Psychiatry Res. 1995 Sep 29;61(3):129-35 [MEDLINE].
10. Wilson, E.O. - "Sociobiology". Harvard University Press, 1992 [AMAZON].
11. Moir A. and Jessel D. - "Brain Sex". 1993 [AMAZON] See also: Excerpts from the book
12. Blum, D. - "Sex on the Brain: The Biological Differences Between Men and Women". Penguin, 1998 [AMAZON]
13. Kimura, D. - "Sex and Cognition". MIT Press, 1999 [AMAZON]

Renato M.E. Sabbatini holds a doctorate in neurophysiology by the Faculty of Medicine of the University of São Paulo at Ribeirão Preto, Brazil, and was a guest scientist and post-doctoral fellow at the Max Planck Institute for Neurobiology in Munich, Germany. He is currently chairman of medical informatics and adjunct professor at the Faculty of Medical Sciences of the State University of Campinas, in Campinas, Brazil; associate editor and chairman of the editorial board of "Brain & Mind" Magazine.

Your brain's sex can make you ill
By Michelle Roberts
BBC News health reporter

Male and female brains look and work differently
Scientists say they have proof that the sex of the brain makes men and women more prone to different diseases.
Doctors know that women are more likely than men to have depression, anxiety or an eating disorder, while men are at higher risk of Parkinson's disease.
Post-mortem and brain imaging studies show that male and female brains are physically different.
Now scientists say they can to link the two together and suggest future disease cures may be "gender-specific".
Male or female brain?
The sex of a brain is decided in the mother's womb and depends, among other factors, on hormone levels.
Higher levels of testosterone makes a male brain and oestrogen a female one.

We should be looking at diseases as male and female

Professor Swaab

Professor Dick Swaab from The Netherlands Institute for Brain Research in Amsterdam,
Brain gender diseases
He said that because men and women's brains are different "we should be looking at diseases as male and female".
"There is a different sex ratio for neurological and psychiatric diseases.
"In depression, it is very clear that sex hormones are directly interfering with the stress axis in the brain.


Women tend to be better at empathising - guessing other's emotions and responding appropriately
Men are generally better at systemising - investigating how a system works
"We have shown that sensitive proteins [receptors] for sex hormones are present in the cells that form the stress axis. In women there are more oestrogen receptors and in men more androgen receptors present.
"That results in higher prevalence of depression in women compared to men because the stress axis is more sensitive.
"The oestrogens are directly affecting the production of the stress peptides.
"So for the same amount of stress in the environment, women are more prone to develop depression than men."
Others have shown that hormone levels could play a part in multiple sclerosis.
Dr Carlo Pozzilli and colleagues at the University La Sapienza in Italy found that women with MS had lower levels of the male hormone testosterone throughout their monthly cycle compared to women who did not have MS.
Dr Glenda Gillies and colleagues at Imperial College London have been looking at Parkinson's Disease, which is far more common in men than in women.
"The idea is that perhaps oestrogen is being neuroprotective so that the neurones that degenerate in PD don't seem to be as susceptible to the processes in women as they are in men," she said.

I think we are realising that drugs have to be personalised

Dr Glenda Gillies, Imperial College London
"It may well be that there is something that has been programmed differently in the brain during early development to make it respond in a different way."
She said that most of the drugs available today had been tested on men, which may mean they are not necessarily the best design for women.
Anita Holdcroft, consultant anaesthetist also from Imperial College London, agrees.
She said not only are male and female brains different, but women's brains change throughout life in relation to fluctuating hormone levels.
"That may well affect disease states and how drugs work."
She scanned the brains of women before and after they were pregnant and found the brain shrank during pregnancy.
The shrinkage was even greater if the woman had a complication of pregnancy called preeclampsia, but reversed by six months after delivery of the baby.

ATLANTA, October 17, 2006 - New research into how sex influences brain function shows surprising and important implications for understanding and treating a variety of neurological diseases, that strike one sex more than another, such as autism, Alzheimer's disease, depression, and schizophrenia.

For more than half a century, scientists believed that gonadal steroid hormones -- "sex" hormones such as testosterone and estrogen -- were solely responsible for differences between male and female brains. Higher levels of testosterone during fetal development, for example, are known to cause the male brain to develop differently than the female brain, triggering cell death in some regions and fostering cell development in others.
In recent years, however, research has suggested that not all sex differences in the brain are the result of steroid action. In studies on mice and songbirds, Arnold and his colleagues have found that the sex chromosome genes within brain cells play an important role in making the brain masculine or feminine.