Sex and the Brain

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The brain is the most important sexual organ [1]. Its structures and functions, which underlie sexual behaviour amongst humans, may be determined by exploring the neurological basis of sexual orientation, sexual attraction, sexual function, sexual addiction, and paraphilia. Recent evidence suggests that there are sexual dimorphisms in the brain such as differentiated hippocampal and hypothalamic responses amongst males and females, with additional differences between heterosexual and homosexual individuals [2][3]. Sexual attraction is influenced by neurotransmitters and pheromones, and sexual functions such as desire, arousal, and erection or orgasm are controlled by the endocrine, neurotransmitter, and central nervous systems [4][5]. Furthermore, sexual behaviour activates the mesolimbic dopamine pathway, which is not only the reward pathway involved in reinforcing survival behaviours, but it is also implicated in sexual addiction [6]. Structural differences, such as decreased gray matter volume in the ventral striatum, orbitofrontal cortex, and cerebellum, are associated with paraphilia [7]. These studies establish that the neuroscience of sexual behaviour is important to study, as it allows one to understand sexual emotions and experiences from different perspectives, gain knowledge of neurological processes, and improve treatments for sexually sadistic behaviours. Sex, although a basic human instinct, involves many structures, factors, and pathways, and is controlled by the most complex human organ, the brain.

Bibliography
1. Dennis, C. Brain development: The most important sexual organ. Nature 427, 390-392 (2004).
2. Pyter, L.M., Kelly, S.D., Harrell, C.S., Neigh, G.N. Sex differences in the effects of adolescent stress on adult brain inflammatory markers in rats. Brain Behav Immun http://dx.doi.org/10.1016/j.bbi.2013.01.075 (2013).
3. Kinnunen, L.H., Moltz, H., Metz, J., Cooper, M. Differential brain activation in exclusively homosexual and heterosexual men produced by the selective serotonin reuptake inhibitor, fluoxetine. Brain Res 1024(1-2), 251-254 (2004).
4. Saxton, T.K., Lyndon, A., Little, A.C., Roberts, S.C. Evidence that androstadienone, a putative human chemiosignal, modulates women’s attributions of men’s attractiveness. Horm Behav 54(5), 597-601 (2008).
5. Meston, C.M., Frohlich, P.F. The Neurobiology of Sexual Function. Arch Gen Psychiat 57(11), 1012-1030 (2000).
6. Tomkins, D.M., Sellers, E.M. Addiction and the brain: the role of neurotransmitters in the cause and treatment of drug dependence. CMAJ 164(6), 817-821 (2001).
7. Schiffer, B. et al. Structural brain abnormalities in the frontostriatal system and cerebellum in pedophilia. J Psychiat Res 41(9), 753-762 (2007).


Paraphilia

main article: Paraphilia
author: luonghe

Weird Love
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Let's talk about some of them[Bibliography item 39 not found.]

The word ‘Paraphilia’ comes from the Greek words ‘para’ and ‘philia’ which refer to the abnormal and attraction aspects of this phenomenon[1], respectively. In other words, paraphilia is defined as a sexual attraction to what is considered outside the range of normal. There are many kinds of paraphilia, even if the definition of paraphilia itself is at times unclear. This ambiguity can be sourced by the fact that, as Dr. Howard Zonana of Yale University states “Distinguishing normal from abnormal sexual behaviours and fantasies is a challenging task,”[2] and not all people with a paraphilia require treatment[1].

Studies done to study distinguishing activity patterns and brain structure features often compare the brains of those with paraphilia and those without. There have been a number of studies that specifically look at the abnormalities present in paedophilia, also known as the sexual attraction to children. Even within paedophilia studies, it has been shown that various cortical areas and structures have a role in behaviour, supporting the idea that the brain processes linked to attraction and sex are present throughout the brain. For example, Sartorius et al. found that there was an increase in amygdala activation in pedophiles when presented with photos of children[4] while Pollok et al. looked at the primary and secondary somatosensory areas to find any abnormal activity in people with masochistic behaviours[3].

Bibliography
1. De Silva, P. (2006) Paraphilias. Psychiatry, 6(3), 130-134.
2. Frieden, Joyce. (2009) DSM-V work on paraphilias begins in earnest. Clinical Psychiatry News, 37(12), 21.
3. Pollok, B., Krause, V., Legrain, V., Ploner, M., Freynhagen, R., Melchior, I. & Schnitzler, A. (2010). Differential Effects of Painful and Non-Painful Stimulation on Tactile Processing in Fibromyalgia Syndrome and Subjects with Masochistic Behaviour. PLoS ONE, 5(12), p. e15804
4. Sartorius, A., Ruf, M., Kief, C., Demirakca, T., Bailer, J., Ende, G., Henn, F. A., Meyer-Lindenberg, A. & Dressing, H. (2008). Abnormal amygdala activation profile in pedophilia. European Archives of Psychiatry and Clinical Neuroscience, 258(5), 271-277.


Sexual Addiction

main article: Sexual Addiction
author: Christine Tsilas

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http://images.idiva.com/media/healthmeup/photogallery/2011/Nov/porncoverh_600x450.jpg

Excessive levels of non-paraphilic sexual behaviour are characterized by the extreme and repetitive expression of culturally adopted sexual behaviours [1] Many terms have been used to describe excessive sexual behaviour, such as compulsive sexual behaviour (CSB), hypersexuality, and sexual addiction [1][2]. Sexual addiction is considered to be a behavioural addiction, however the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) does not recognize sexual addiction as a disorder [3][4]. There is controversy as to whether it should be classified as an impulsive control disorder, an obsessive-compulsive disorder, or if it even exists [1][5]. However, behavioural addictions have recently been shown to share the same core features as substance addiction [6]. This includes a loss of control of sexual urges, behaviours, and thoughts, as well as tolerance, withdrawal, and continuing despite adverse consequences [1][6]. Sexual addiction is thought to take many forms, such as compulsive masturbation, extensive pornography use, and multiple affairs [1]. Also, sexual behaviour and substance use activate the same brain pathway (the mesolimbic dopamine pathway) which is the reward circuit involved in reinforcing survival behaviours [6][7]. Functional neuroimaging of patients with brain trauma has shown that lesions in the prefrontal cortex and temporal lobes are associated with hypersexuality and loss of inhibition [8]. Also, frontal lobe damage has been thought to lead to CSB [9]. Pharmacological treatments for sexual addiction such as selective serotonin reuptake inhibitors (SSRIs) and antiandrogens have been shown to decrease the frequency and intensity of sexual urges, and allow for greater control over obsessive thoughts and behaviours [10]. Psychotherapy and self-help groups are also effective in treating sexual addiction [10].

Bibliography
1. Garcia, F.D., Thibaut, F. Sexual Addictions. Am J Drug Alc Abuse 36, 254-260 (2010).
2. Coleman, E. Compulsive Sexual Behavior: What to Call it, How to Treat it? SIECUS Report. 31(5), 12-16 (2003).
3. Stein, D.J., Hollander, E., Rothbaum, B.O. (31 August 2009). Textbook of Anxiety Disorders. American Psychiatric Pub. pp. 359–. ISBN 978-1-58562-254-2. Retrieved 24 April 2010.
4. Parashar A, Varma A (April 2007). "Behavior and substance addictions: is the world ready for a new category in the DSM-V?". CNS Spectr 12 (4): 257; author reply 258–9. PMID 17503551.
5. Giles, J. No Such Thing as Excessive Levels of Sexual Behavior. Arch Sex Behav 35(6), 641-642 (2006).
6. Taber, K.H., Black, D.N., Porrino, L.J., Hurley, R.A. Neuroanatomy of Dopamine: Reward and Addiction. J Neuropsych Clin N 24(1), 1-4 (2012).
7. Tomkins, D.M., Sellers, E.M. Addiction and the brain: the role of neurotransmitters in the cause and treatment of drug dependence. CMAJ 164(6), 817-821 (2001).
8. Rees, P.M., Fowler, C.J., Maas, C.P. Sexual function in men and women with neurological disorders. Lancet 369(9560), 512–525 (2007).
9. Coleman, E. Neuroanatomical and neurotransmitter dysfunction and compulsive sexual behavior. J.S. Hyde (Ed.), Biological Substrates of Human Sexuality, American Psychological Association, Washington, D.C. pp. 147–169 (2005).
10. Raymond, N. An Approach to Pharmacotherapy of Compulsive Sexual Behavior. SIECUS Report. 31(5), 17-18 (2003).


Sexual Attraction

main article: Sexual Attraction
author: Anurag Ranjit

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What occurs during sexual attraction, and what parts of the brain
are involved in such an important process in the human life cycle?[3]

Sexual attraction is the first step in the process that leads to one of the fundamental instincts of any living organism, sexual reproduction. It is an essential step leading to reproduction and different organisms have different ways of making themselves seem more attractive to the other gender. There is evidence that attraction is gender dependent as there seems to be different regions of the brain that get activated when a person is attracted to someone else. Men seem to focus more on visual stimuli, such as physique and face, while women seems to focus more on emotional connections with their partner. However there are some areas that are activated in both genders, mainly the dopamine reward system[1]. There are other factors that play a role in the process of sexual attraction, such as pheromones released by the other person or neurotransmitter ratios in the brain. Asexuality is most often described as the lack of sexual attraction, but can be described in multiple ways. There is limited research concerning asexuality, but the research that has been done have identified certain aspects of sexual life which can help define asexuality.[2]

Bibliography
1. Zeki S. The neurobiology of love. FEBS Lett 14, 2575-2579 (2007)
2. Lori A. Brotto et al., Asexuality: A mixed methods approach. Archives of Sexual Behaviour 39, 599-618 (2010)


Sexual Dimorphisms

main article: Sexual Dimorphisms
author: TGiritharann

The Two Brains
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The battle between the sexes has been an eternal one. No one likes to lose the battle and it is more pleasant to believe that men and women are of equal ability and equal mind. In the past, sexual differences in the brain have been especially disregarded due to the belief that they are of little to no significance[1]. However, in recent research, an increasing amount of evidence suggests otherwise. Differentiated hippocampal and hypothalamic responses to stress and stimulating imagery can be found between males and females[2], with further differences between heterosexual and homosexual individuals[3]. Sexually dimorphic brain systems are useful to understand when tailoring more efficient therapies to those with disease states where sexual differences have been found. These disorders include a wide array involving emotional imbalance, such as schizophrenia [4] and depression [5]. Additionally, the neurological processes underlying sexual orientation and identification allow one to more objectively analyze how different sexual experiences arise and their associated social implications[1].

Comedic approach to the differences in the brain. Note that this is purely "comedy" but it
highlights interesting stereotypes of the brains between males and females that
can sometimes perpetuate the stigma of analyzing the scientific basis of these differences.
Bibliography
1. Rahman, Q. The neurodevelopment of human sexual orientation. Neuroscience and Behavioural Reviews. (2005). http://dx.doi.org.myaccess.library.utoronto.ca/10.1016/j.neubiorev.2005.03.002.
2. Pyter, LM., Kelly, SD., Harrell, CS., Neigh, GN. Sex differences in the effects of adolescent stress on adult brain inflammatory markers in rats. Brain Behav. Immun. (2013), http://dx.doi.org/10.1016/j.bbi.2013.01.075.
3. Kinnunen, LH., Moltz, H., Metz, J., Cooper, M. Differential brain activation in exclusively homosexual and heterosexual men produced by the selective serotonin reuptake inhibitor, fluoxetine. Brain Res. (2004) 1024(1-2):251-254.
4. Scholten, M., Aleman, A., Montagne, B., Kahm, R. Schizophrenia and processing of facial emotions: Sex matters. Schizophrenia Research. (2005). http://dx.doi.org.myaccess.library.utoronto.ca/10.1016/j.schres.2005.06.019.
5. Kong, L. et al. Sex differences of gray matter morphology in cortico-limbic-striatal neural system in major depressive disorder. Journal of Psychiatric Research. (2013). http://dx.doi.org.myaccess.library.utoronto.ca/10.1016/j.jpsychires.2013.02.003.


Sexual Function and The Brain

main article: Sexual Function and The Brain
author: Paramanathan

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What goes on in the brain before, during, and after sex?
Image Source: www.brainsex.eventbrite.com

People engage in sexual activities for numerous reasons, mainly for pleasure or as a method of reproduction. Sexual function, which is defined by sexual desire, sexual arousal, and ejaculation or orgasm, is an important part of human nature. It is controlled by the endocrine system, neurotransmitter system, and central nervous system, all of which are involved in the excitation or inhibition of various neurochemical pathways or neuroanatomical structures [1]. Sexual desire is the craving for positive, sexual reinforcement through sexual activity, which leads to sexual arousal [2]; this state stimulates the enjoyment of sexual pleasure with the goal of ejaculation or orgasm [3]; ejaculation is the release of semen by males and orgasm is the discharge of sexual tension by males and females [4]. These conditions are excited or inhibited depending on the activity of various brain systems [1].

Bibliography
1. Meston, C., & Frolich, P. (2000). The Neurobiology of Sexual Function. Archives of General Psychiatry, 57(11), 1012-1030. Retrieved from http://archpsyc.jamanetwork.com.myaccess.library.utoronto.ca/article.aspx?articleid=481665
2. Pfaus, J. (2009). Pathways of Sexual Desire. Journal of Sexual Medicine, 6(6), 1506-1533 . Retrieved from http://journals1.scholarsportal.info.myaccess.library.utoronto.ca/tmp/13769080579032254984.pdf
3. Bancroft, J. (2005). The Endocrinology of Sexual Arousal. Journal of Endocrinology, 186(3), 411-427. Retrieved from http://joe.endocrinology-journals.org.myaccess.library.utoronto.ca/content/186/3/411.full
4. Haeberle, E. (1983). The Sex Atlas. New York: The Continuum Publishing Company. Retrieved from http://www2.hu-berlin.de/sexology/ATLAS_EN/index.html



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