Allen, L. S., & Gorski, R. A. (1991). Sexual dimorphism of the anterior commissure and massa intermedia of the human brain. Journal of Comparative Neurology, 312, 97-104. Allen, L. S., & Gorski, R. A. (1992). Sexual orientation and the size of the anterior commissure in the human brain. Proceedings of the National Academy of the Sciences, USA, 89, 7199-7202. Allen, L. S., Hines, M., Shryne, J. E., & Gorski, R. A. (1989). Two sexually dimorphic cell groups in the human brain. Journal of Neuroscience, 9, 497-506. Anderson, R. H., Fleming, D. E., Rhees, R. W., & Kinghorn, E. (1986). Relationship between sexual activity, plasma testosterone, and the volume of the sexually dimorphic nucleus of the preoptic area in prenatally stressed and non-stressed rats. Brain Research, 370, 1-10. Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27-31. Blanchard, R., & Klassen, P. (1997). H-Y antigen and homosexuality in men. Journal of Theoretical Biology, 185, 373-378. Cantor, J. M., Blanchard, R., Paterson, A. D., & Bogaert, A. F. (2002). How many gay men own their sexual orientation to fraternal birth order? Archives of Sexual Behavior, 31, 63-71. Dorner, G. (1979). Psychoneuroendocrine aspects of brain development and reproduction. In L. Zichella & P. Pancheri (Eds.), Psychoneuroendocrinology in reproduction: An interdisciplinary approach (pp. 239-252). Amsterdam: Elsevier. Flowers, P., & Buston, K. (2001). "I was terrified of being different": Exploring gay men's accounts of growing-up in a heterosexist society. Journal of Adolescence, 24, 51-65. Gooren, L. J., & Kruijver, F. P. M. (2002). Androgens and male behavior. Molecular and Cellular Endocrinology, 198, 31-40. Kula, K., & Slowikowska-Hilczer, J. (2000). Sexual differentiation of the human brain. Przeal Lek, 57(1), 41-44. LeVay, S. (1991). A difference in hypothalamic structure between heterosexual and homosexual men. Science, 253, 1034-1038. Looy, H. (1995). Born gay? A critical review of biological research on homosexuality. Journal of Psychology and Christianity, 14, 197-214. Mbugua, K. (2003). Sexual orientation and brain structures: A critical review of recent research. Current Science, 84, 173-178). Swaab, D. (2008, July 29). Sexual orientation and its basis in brain structure and function. PNAS, 105(30), 10273-10274. Swaab, D., Chung, W., Kruijver, F., Hofman, M., Ishunina, T., (2002). Sexual differentiation of the human hypothalamus. Advances in Experimental Medicine and Biology, 511, 75-100. Swaab, D. F., & Fliers, E. (1985). A sexually dimorphic nucleus in the human brain. Science, 228, 1112-1115. Swaab, D. F., & Hofman, M. A. (1990). An enlarged suprachiasmatic nucleus in homosexual men. Brain Research, 537, 141-148. Swaab, D. F., & Hofman, M. A. (1995). Sexual differentiation of the human hypothalamus in relation to gender and sexual orientation. Trends in Neurosciences, 18, 264-270. Ward, I. (1972). Prenatal stress feminizes and demasculinizes the behavior of males. Science 7, 175(4017), 82-84. Wilson, G., & Rahman, Q. (2005). Born gay: The psychobiology of sex orientation. London, England: Peter Owen Publishers. Wolchover, N. (2012, June 12). Why are there gay men? because women who inherit 'gay genes' have more kids, scientists say. Huffington Post. Retrieved from http://www.huffingtonpost.com/2012/06/12/why-are-there-gay-men_n_1590501.html?utm_hp_ref=gay-voices&ir=Gay Voices
Brain development final presentation currie
Biological Causes for the Homosexual Brain BRYAN CURRIE BRAIN DEVELOPMENT OF YOUTH HDFS 892 MICHIGAN STATE UNIVERSITY
Why Study Homosexual Brain Development?Puberty – the amazing time whenadolescents realize their sexual attractionsand abilities – is both exciting and terrifying.During puberty, heterosexual youth may beconfused by their newfound attractions, butare assured by their culture that they are“normal.”Homosexual youth, however, are not asfortunate. From a very early age, lesbian,gay, bisexual, and transgender (LGBT) youthare often keenly aware that they are“different” (Flowers & Buston, 2001). Inaddition to figuring out the “normal”struggles of sexual attraction, LGBT youth It is important for youth developmentoften question whether they are broken, professionals to understand theoriesstrange, or immoral because their attractions surrounding the development of the homosexualaren’t like everyone else’s. Some of these brain so that they can assure frightened LGBTyouth even pursue dangerous therapies to try youth that their newly discovered desires areto “fix” their sexual orientation. simply a part of their beautiful design.
The Homosexual Brain: Premise and Thesis Premise: Various in-utero factors may affect the development of the homosexual brain so that both its form (i.e. physical structure) and function (i.e. sexual attraction) are slightly different from the heterosexual brain. Thesis: Although both nature (genetics and/or biology) and nurture (environment, etc.) may play a role in the development of sexual orientation, this presentation will focus on biological theories for homosexual brain development. Biological theories include the ways hormones affect the fetus in-utero and should not be confused with genetic theories, which include the search for the “gay gene.” In addition to discussing the formation of the homosexual brain, this presentation will also explore whether the brains of homosexual youth are physically different from those of their heterosexual peers.Disclaimer: It is important to understand that “masculine” and “male” are not synonyms. Gay menare neither inherently less “masculine” nor “male” simply because of their sexual orientation.Although many of the studies referenced in this report refer to the “masculine” or “feminine” brain, itshould be understood that these words refer to biological differentiation of the brain (ie. whether it isstructured more like a male brain or a female brain). These words are not intended to comment onthe masculinity/femininity (i.e. culturally defined behavior) of homosexual people.
Biological Theories of Development THE HOMOSEXUAL BRAIN
Major Biological TheoriesThere are two major theories for biological (in-utero)causes of homosexuality: The mother may produce an immune reaction that prevents the male brain from developing in a typically “masculine” pattern. The hormone wash which “defeminizes” the brain in-utero is disturbed due to maternal stress.
Maternal Immune Reaction IT HAS BEEN SUGGESTED THAT THE MALE FETUS MAY SOMETIMES PRODUCE ANIMMUNE RESPONSE IN THE MOTHER WHICH TRIGGERS THE RELEASE OF ANTIBODIES. THESE ANTIBODIES CHANGE THE FETUS’S BRAIN DEVELOPMENT AND CAUSE A HOMOSEXUAL ORIENTATION.
Maternal Immune Reaction: AntigensAntigen: any substance foreign to the body that evokes an immune responsefrom the host.Because of a male child’s XY gene structure, HY antigens arepresent on the surface of his developing cells. Because theexpectant mother is used to having only XX cells in her body,Blanchard and Bogaert (1996) propose that when the male fetus’sHY antigens are released into the mother’s bloodstream, her bodymay trigger the immune system to release HY antibodies. Theseantibodies cross the placenta and enter into the male fetus’sdeveloping brain.HY antigens help the male fetus develop sex-typical traits.Exposure to HY antibodies (which attack and potentially weaken theHY antigens) may therefore affect subsequent sexual behavior inmen, increasing the likelihood that the male child will be moreattracted to men than women (Blanchard & Klassen, 1997).
Maternal Immune Reaction: EvidenceIn most cases, a mother’s immune system becomesstronger with every pregnancy. Therefore, each timea mother carries a male fetus, the chances increasethat her body will develop an immune response tohis HY Antigens.This may explain why male homosexuality correlateswith birth order. Each additional older brotherincreases the likelihood a male child will behomosexual by 33% (Blanchard & Klassen, 1997;Cantor, Blanchard, Paterson, & Bogaert, 2002).
Maternal Immune Reaction: EvidenceNew research has, however, begun to question whether having multiple male childrenis a cause of homosexuality (due to an immune reaction) or an evolutionary product ofthe “gay gene.” According to research that will be published in an upcoming issue ofthe Journal of Sexual Medicine: “the same genetic factors that induce gayness in males also promote fecundity (high reproductive success) in those males’ female maternal relatives” (Wolchover, 2012,). If there is a “gay gene” it likely resides on the X chromosome. Evolutionary biologists suggest that the presence of this gene in mothers may “increase androphilia, or attraction to men, thereby making the males who possess the gene homosexual and the females who possess it more promiscuous” (Wolchover, 2012). If this theory holds true, larger family sizes may not be the cause of homosexual male children, but rather an evolutionary result of the “gay gene” as it is carried by women on the X chromosome.
Hormone Wash ALL FETUSES BEGIN BIOLOGICALLY FEMALE. A WASH OF TESTOSTERONED U R I N G T H E 1 2 - 1 4 TH W E E K S O F P R E G N A N C Y PRODUCES A MASCULINE BRAIN. DISRUPTIONS IN THIS PROCESS MAY PREVENT THE BRAIN FROM BECOMING FULLY MASCULINE.
Hormone Wash: AndrogensAndrogen: A steroid, such as testosterone, that controls the developmentand maintenance of masculine characteristics.If a fetus carries the XY chromosome, testosterone is needed to activate thenewly forming hypothalamus into a male brain. This process is called“defeminization” (Kula & Sowikowska-Hilczer, 2000).Different levels of testosterone exposure during this process influence “thestructure and function of brain regions that control the direction of sexualattraction” (Wilson & Rahman, 2005, p. 70).Because the genitals are developed during a different period of gestationand through a different process than the defeminization of the brain, thepresence of a masculine body does not necessarily indicate the presence ofa masculine brain. This may partially explain why the brain structure ofhomosexual males may more closely resemble that of heterosexual females.
Hormone Wash & Maternal StressDuring the 12th to 14th week of pregnancy, a developing male fetus will receive a wash of androgens (testosterone) over its brain. This hormone wash defeminizes it and differentiates it into the male form (Gooren & Kruijver, 2002). If a mother is stressed during the early stages of pregnancy, she will release anadrenaline related hormone. This hormone (androstendione) is structurally similar to testosterone, but affects the fetus differently.Because the stress hormone seems to mimic testosterone, the wash of testosterone is less effective, causing a disturbance in the "defeminization" of the hypothalamus (Swab, Chung, Kruijiver, Hofman, & Ishunia, 2002) and preventing “normal” sex differences in the brain to be acquired (Looy, 1995).
Hormone Wash: EvidenceIngebog Ward (1972) tested this theory in studies of pregnantrats. Ward divided pregnant rats into three groups. Shesubjected the first group to stress during the first ten days ofgestation by irritating the mothers with bright lights, noiseand vibrations. Ten days in a rats pregnancy corresponds tothe first trimester (3 months) of human pregnancy. Thesecond group was subjected to stress during the end of theirpregnancy, just before birth. The third group was comprisedof male offspring from both prenatal stressed mothers andunstressed mothers.Dr. Ward then allowed all the males to grow to adulthoodwithout further interference. The sexually mature male ratswere placed in cages with healthy females to observe theirability and desire to mate with normal adult females.
Hormone Wash: EvidenceInstead of trying to “mount” Ward concluded thatfemale rats, the stressed males “exposure of pregnantallowed themselves to be rats to environmental Stress duringmounted. This was attributed stressors modifies the pregnancyto stress caused reactions normal process of seems toduring critical stages of sexual sexual behavior preventdifferentiation. “Specifically, it differentiation in male testosteroneappears that stress causes an fetuses by decreasing fromincrease in the weak adrenal functional developing aandrogen, androstendione, from testosterone and brain that isthe maternal fetal adrenal elevating sexuallycortices, or both, and a androstenedione attracted toconcurrent decrease in the levels during prenatal females.potent gonadal androgen, development”testosterone” (Ward, 1972, p. (Ward, 1972, p. 83).82).
Brain DifferencesIt has been shown that thebrains of heterosexualmales, homosexual males,heterosexual females, andhomosexual femalesfunction differentlyand aredifferently structured.* It is not clear if the differencesbetween the homosexual andheterosexual brain are due to biologicalfactors, genetic factors, or conditioning.
Structural DifferencesMany of the structural differences between the homosexualand heterosexual brain are found in the hypothalamus, theregion of the brain that controls how humans experiencesexual attraction (Dorner, 1979).These differences may be containedin any of three regions: Sexually Dimorphic Nucleus (SDN) Suprachuiasmatic Nucleus (SCN) Anterior Commissure (AC)
Structural Differences: SDNThe sexually dimorphic nucleus (SDN) is a cluster of cells in the preoptic area of thehypothalamus. The SDN is believed to help regulate sexual behavior(Allen, Hines, Shyne, & Gorski, 1989; Anderson, Fleming, Rhees, & Kinghorn, 1986). The SDN is commonly 2.5x larger in males than females, containing 2.2x more cells (Swaab & Fliers, 1985). Researchers hypothesize that brains attracted to women (heterosexual men and homosexual women) should have a lager SDN. Sections of the SDN, known as INAH 3, have been shown to be up to 3x larger in heterosexual men than heterosexual men (LeVay, 1991).* These findings (that both heterosexual women and homosexual men have a smaller SDN) seem to indicate that male homosexual brain structure influences/causes a sexual attraction to men.*The study referenced (LeVay, 1991) was performed on post-mortem AIDS patents.Some researchers question the study’s findings, claiming that the enlarged INAH 3 regionfound in homosexual men may be a result of the AIDS virus.
Structural Differences: SCNThe suprachiasmatic nucleus (SCN) is a small region in the brain’s midline.It is responsible for regulating circadian rhythms (i.e. body functions in a 24hour cycle) and has been associated with reproductive processes (Swaab &Hofman, 1995). The SCN has been shown to be 1.7x larger in homosexual males than in heterosexual males, containing 2.1x more cells (Swaab & Hoffman, 1990). Swaab produced a similar difference in rats by disturbing the interaction between testosterone and the developing brain. The experiment yielded bisexual rats that had a significantly larger SCN. Swaab (2008) suggests that his tests on rats indicate that the larger SCN in homosexual males is not caused by their behavior (nurture), but rather “by an atypical interaction between sex hormones and the developing brain” (p. 10273).
Structural Differences: Anterior Commissure The Anterior Commissure (AC) is a fiber tract that is responsible for transmitting sensory information between the brain’s temporal lobes (Harrison, 1994). The AC is typically larger in women than in men (Allen & Gorski, 1991). The AC of homosexual men has been shown to be 18% larger than heterosexual women and 34% larger than heterosexual men (Allen & Gorski, 1992). While the AC is not associated with reproductive functions, it is related to cognitive abilities and language (Swaab, 2008). The presence of a larger AC may explain why homosexual men seem to display many “feminine” brain functions (see “functional differences” above).
BibliographyBibliographical references can be found in the notessection below.