Sexual Differentiation
in Cognitive Functioning
and the Human Brain
external image male-female.jpg


Intro
Sexual Differentiation refers to differences in form and function between male and female brains. It is most often studied within the context of human intelligence, but it has also proven to be of interest to researchers interested in the cause and treatment of various mental disorders as well as brain injuries. The subject has spawned many different theories throughout time, from the extremely primitive to theories based upon complex analysis of MRIs and other advanced scientific methods.

Theories

Early Brain Size Theory

Early Brain size theory developed from a deep social desire to prove the superior intelligence levels of the white male.
This theory focused on the size and weight differences between men and women, with the earliest form of measurement relying solely on craniometry ( the measurement of skulls) and later measurements including weighing wet brains (Gould, 1981).

These theories were being studied by leaders in the field such as: Charles Darwin, Paul Broca, and Gustave Le Bon who documented some of the first research on the subject of brain differences. Each of these men were determined to prove that men were superior to women (Gould, 1981). The actual research shows that, on average, men's brains are 11-12 percent heavier than a woman's and 2 percent larger than a woman's (Rushton & Ankney, 2009). For these early researchers, this difference in size and weight was enough proof to claim that women were not as intelligent as men. Broca went on to say that this not only showed that women were mentally not as intelligent but were also physically less capable (Gould, 1981) .

Implication
Because early research in this area was carried out with the specific intent of proving the societal biases against women and minorities, the results simply acted as support for the already oppressive way that these groups were being treated. Based upon these conclusions, women and minorities continued to be denied educational experiences equal to those of their white male counterparts. In later years, however, new researchers, eager to definitively prove whether there was in fact a connection between brain size and intelligence, adopted the theory. These researchers, using less bias and more technologically sound practices, then created what we have chosen to call Late Brain Size Theory.

Issues
Because of the inherent biases present in their own beliefs, many of the early studies were designed to produce results that supported the belief that white males possessed larger brains and thus superior intellect. The idea of using simplistic measurements to prove their points only became problematic for researchers when they realized that they were finding African American men with the same or even larger skulls than some of their white subjects. Although later research has proven that there is in fact a correlation between brain size and IQ (Rushton & Ankney, 2009), these early methods were not enough to provide a true understanding of either brain size or intelligence, as thorough and unbiased IQ testing had not been developed at this time (Gould 1981). Another issue with this was that these researchers were not considering the fact that women were structurally different as well, researchers failed to take overall body mass into consideration when comparing brain sizes.



Late Brain Size Theory

For the later researchers who took on the challenge of providing a definitive answer as to the relationship between brain size and intelligence, new high tech options completely changed the nature of the study of the brain. Now, through technology such as the MRI and standardized intelligence testing, new forms of supposedly unbiased information can be gathered and easily compared with the work of others.

Implications
Some researchers believe this general size difference between male and female subjects' brains provides an explanation for the improved spatial skills seen when testing many male subjects. According to Rushton and Ankey (2009), men's brains measured 100 grams heavier than women's brains before being corrected for weight, and 140 grams heavier when weight was accounted for in the measurement. This led to the further conclusion that the average number of neurons contained within a female brain is approximately 19 billion while the average within the male brain is approximately 23 billion. For those who believe this to be true, the increased brain size (and thus extra neurons) may provide more computing power for the more difficult spatial tasks (Rushton & Ankey, 2009).

external image brain_anatomy.jpg
Issues
Although many researchers agree that there is a correlation between brain size and IQ, they do not all agree that there is enough evidence to indicate a gender difference in the findings. Researchers such as Peters (1995) believe that the methods being used to scale male and female brains according to body size are not proving accurate. Peters states that the methods being used are not appropriate when studying within species groups, and new methods and procedures must be developed if one wants to provide concrete evidence that there is a gender difference (Peters, 2009).


Uterine Blood Flow Theory

Supporters of this theory believed that a disruption in uterine blood flow could lead to things such as hysteria and other medical conditions. Many of the early information on the subject stems from the writing of Charlotte Perkins Gilman, a woman who suffered from common symptoms of hysteria and those of her husband, a physician, who saw it fit to develop methods for dealing with her condition (Gilman, 1892). Women who were believed to suffer from Hysteria were treated by a physician or midwife massaging the clitoris and other areas to reach orgasm. Doctors also introduced vibrators to help in this treatment of this ailment. When women would orgasm, this would increase their blood flow therefore treating the symptoms and causing the women to relax and become more calm (Mianes, 1999).

Implications

Improving the blood flow to the brain was not going to treat or remove hysteria. This type of treatment never produced long term positive results or cured the ailment. This was thought to be a widespread problem with little hope for the woman to benefit which left the woman permanently at the mercy of her physician for help (Maines, 1999)

Issues
The problem with this is at the time there was little known and developed about psychological issues. These women could have suffered from a multitude of other mental disorders which had not yet been thoroughly studied; however, none of them would have been properly handled by this method . There needed to be evaluations and an understanding of what was really going on. Although an orgasm could have relaxed the person for a brief time, it would in no way be a proper form of medical treatment. The women were never cured from these methods and many physicians did not want to or enjoy this act because it was something that was needed for the remainder of their lives and required skill to complete (Maines, 1999). In many instances this job was passed on to midwives to prevent the doctor from having to perform this labored and exact method (Maines, 1999).


Prenatal Hormone Theory

According to prenatal hormone theory, when fetuses are exposed to higher than normal levels of androgens during an especially sensitive period of their development (presumed to occur in humans in early to mid gestation) these hormones not only affect genital development, but they also cause the brain to take either a distinctly male or female route in development. Proponents of this theory believe that, depending on whether the androgen exposure triggered male or female development, the brain will wither be organized for masculine or feminine behavior after birth. Supporters of this theory often ascribe to the belief that females are more developed verbally and males are stronger in spatial skills based upon this supposed reorganization of the brain. (Finegan, Bartleman, & Wong, 1989)

Implications
An offshoot of Prenatal Hormone Theory, known as the Extreme Male Brain theory, has used the basic tenets of this research to propose an explanation for autism. They believe that the reduced verbal skills, inability to distinguish nonverbal communication, and diminished capability to use Theory of Mind commonly seen in autistic individuals can be attributed to a higher than normal amount of androgren exposure in the womb. According to this theory, the brains of these individuals not only differentiated in traditionally masculine ways, but did so to such a degree that it was detrimental to the other areas of the brain not affected by the androgens. The fact that autism occurs much more frequently in males than in females is said to lend credibility to this theory, as does the test scores achieved by autistic individuals on sex specific testing. Subjects with autism have been found to perform poorly on tests that females normally have an advantage over, such as emotion reading tests, but frequently outperform other subjects on tasks that males are generally considered superior on, such as embedded figures. If this theory holds true, it might eventually lead to a cure for this increasingly prevalent disorder (Knickmeyer & Baron-Cohen, 2006).

Issues
Much of the data supporting this theory is drawn from research performed by prenatally exposing animals to high levels of androgens and then measuring their performances on a variety of tasks. Although animal research is helpful to guide psychologists in the proper direction, the results should not automatically be assumed to carry over to human population. Also when studies have relied on human participants, testing has tended to focus on groups of individuals outside the genetic norm, so there may be other confounding factors affecting the results that are not being identified (Finegan, Bartleman, & Wong, 1989).

Gray Matter Vs White Matter Theory

Fascinated by the idea of sex based performance advantages in various subjects, many researchers have attempted to provide a definite answer as to why this performance difference exists. One proposed explanation revolves around the percentages of gray matter and white matter in areas of an individual's brain. Gray matter is considered to be more densely packed with neurons; if a particular area of the brain contained higher than average amounts of neurons it could be hypothesized that that area would in fact be more developed. (Luders, Gaser, Narr, & Toga, 2009)

Implications
If women were, in fact, found have a higher percentage of gray matter in the areas of the brain that controlled emotion processing while
men possessed more gray matter in areas of the brain traditionally believed to handle mathematical skills, this would provide scientific backing for the yet to be proven theory that women and men excel in different subject areas.

This area of study has been further developed by researchers who are applying their new knowledge of gray matter in relation to performance tasks and applying it to the study of elderly subjects in the hopes of potentially developing a standardized process to distinguish between the effects of normal aging and those caused by neurodegenerative diseases (Taki, Kinomura, Sato, Gato, Kawashima, & Fukuda, 2011)
Issues
Researchers disagree over whether or not the differing volumes of gray matter and white matter contained within a brain can truly be attributed to sex differences, or whether or not it is affected by the overall size of the brain. There are even cases of research papers that report size has no effect on the overall percentage of gray matter which, at the same time, contain data that contradicts their reported findings (Luders, Gaser, Narr, & Toga, 2009).


Verbal/ Visual-Spatial Lateralization Theory

Proponents of the Verbal/Visual-Spatial Lateralization theory believe that the hemispheres within the brain are highly specialized to each focus on specific types of tasks, for example the connection between the left hemisphere and language processing. Some believers also take this a step further and suggest that the gender of a subject will affect which side of the brain is more developed and functions at a higher level.

Implications
Belief in this theory has led to a disturbing trend in which students are channeled into one subject or another based upon perceived performance differences. One study showed that girls as young as 9 already showed a significant preference for language based activities compared to math, a trend that the researchers related to the reduced number of females pursuing careers in fields characterized by heavy reliance on math skills (Steffens, Jelenec, & Noack, 2010).
Issues
One major issue surrounding this theory is the fact that researchers have repeatedly been able to increase subjects scores on tests that traditionally generate higher scores from the opposite sex. For example, one study found that when women provided with a gender stereotype activating task that made them imagine themselves as a traditionally masculine character, they later scored higher on mental rotation tasks (Ortner & Sieverding 2008). A similar study provided male subjects with a priming task that required them to use a local processing strategy (generally used by females) then ask them to identify nonverbal clues to emotion. Similarly to the previous experiment, the subjects performed with scores more typically expected from the opposite gender (Schmid, Mast, Boombari, & Mast 2011). The results of these two experiments provide us with an alternative view of non congruent gender performance that relies more on social gender priming than on an innate biological difference in functioning.




Brain Type Theory

In 2005, Baron-Cohen published a review of the most recent findings about the biological differences between the male and female brains. He spoke at length about the idea of the three brain types: the “e” type brain (empathizing), also known as the female brain, the “s” (systems) type brain, also known as the male brain, and the balanced type which includes an even amount of the other two types of brain (Baron-Cohen, 2005). He states that at 12 months, female babies seem to have more empathy than boys, and imply that boys are not as good at sharing and other social activities as girls. He also suggested that boys were more overtly aggressive, and girls were covertly aggressive. He also espoused a belief that these girls would grow into women who tend to show empathy to friends and “listen to their problems” (Baron-Cohen, 2005).
external image femalemale.jpg

Implications
The implications of these theories could lead to further gender stereotyping and a self-fulling proficiency. If we follow the different brain theories strictly, we stereotype males and females. Simply looking at the names of the types of brains, how they are known as "male" or "female" we can be lead to believe that the issue is black and white. Even though there is a balanced type, some people will look at the names of these types of brains and automatically place with with the sex they belong with. Therefore, some will automatically believe that men have men type brains and women have women type brains.
Issues
According to Schoppe-Sullivan et al. (2006), the amount of emotional sensitivity shown towards infants varied with both the gender of the infant and the gender of the parents with mothers, often the primary caregiver, showing less emotional attachment to sons than daughters. Baron-Cohen mentioned that as young infant girls seem to enjoy seeing people's expressions more whereas boys are more content with watching a mobile (Baron-Cohen, 2005). This could easily be explained by the perceptions of the parents and subsequent conditioning of the infant. Taking this into consideration, it is possible that girls get more comfort from expressions when upset because they are more accustomed to this type of interaction from their parents while the male infants have learned self soothing techniques by necessity.


References
Baron-Cohen, S. (2005). The essential difference: The male and female brain. Phi Kappa Phi Forum, 85, 23-26. Retrieved October 26, 2011, from MasterFILE Premier.

Finegan, J., Bartleman, B., & Wong, P. Y. (1989). A window for the study of prenatal sex hormone influences on postnatal development [Electronic version]. Journal of Genetic Psychology , 150 (1), 101-112. Retrieved October, 19, 2011 from Academic Search Premier

Gilman, C. (1892). The Yellow Wallpaper. The New England Magazine.

Gould, S. J. (1996). The Mismeasure of Man, 2nd ed. New York: Norton and Company.

Knickmeyer, R. C., & Baron-Cohen, S. (2006). Fetal testosterone and sex differences in typical social development and in autism. Journal of Child Neurology , 21 , 825-845. doi:10.2310/7010.2006.00213

Luders, E., Gaser, C., Narr, K. L., & Toga, A. W. (2009). Why sex matters: Brain size independent differences in gray matter distributions between men and women. The Journal of Neuroscience, 29(45), 14265-14270. doi:10.1523/​JNEUROSCI.2261-09.2009

Maines, R. (1999). "Hysteria," the Vibrator and Women's Sexual Satisfaction. The John Hopkins University Press .

Ortner, T., & Sieverding, M. (2008). Where are the gender differences? Male priming boosts spatial skills in women. Sex Roles, 59, 274-281. doi:10.1007/s11199-008-9448-9

Peters, M. (1995). Does brain size matter? A reply to Rushton and Ankney. Canadian Journal of Experimental Psychology, 49, 570-576. doi:10.1037/1196-1961.49.4.570

Rushton, J. P., & Ankey, C. D. (2009). Whole brain size and general mental ability: A review. International Journal of Neuroscience,, 119, 692-732. doi:10.1080/00207450802325843

Schmid, P. C., Mast, M. S., Bombari, D., & Mast, F. W. (2011). Gender effects in information processing on a nonverbal decoding task. Sex Roles, 65(1/2), 102-107. doi:10.1007/s11199-011-9979-3

Schoppe-Sullivan, S. J., Diener, M. L., Mangelsdorf, S. C., Brown, G. L., McHale, J. L., & Frosch, C. A. (2006). Attachment and sensitivity in family context: the roles of parent and infant gender. Infant & Child Development, 15, 367-385. doi:10.1002/icd.449

Steffens, M. C., Jelenec, P., & Noack, P. (2010). On the leaky math pipeline: Comparing implicit math-gender stereotypes and math withdrawal in female and male children and adolescents. Journal of Educational Psychology, 102, 947 -963. doi:10.1037/a0019920

Taki, Y., Kinomura, S., Sato, K., Gato, R., Kawashima, R., & Fukuda, H. (2011). A longitudinal study of gray matter volume decline with age and modifying factors. Neurobiology of Aging, 23, 907-915. doi:10.1016/j.neurobiolaging.2009.05.003