Sexuality is influenced by biological, psychological, and social factors. The human sexual response cycle involves four phases: excitement, plateau, orgasm, and resolution. Sexual orientation has biological roots in genes, hormones, brain structure, and behavior. Individual differences exist, but attitudes toward sexuality are changing.

1. Sex
Brian J. Piper, Ph.D.

2. History
• 1524: Pietro Aretino & Marcanonio Raimonbi accompany 16
pornographic engravings with sonnets in I modi
• 1923: Sigmund Freud publishes the “The Ego and the Id”
• 1948: Alfred Kinsey publishes “Sexual Behavior and the Human Male”
• 1957: FDA approves “the pill”
• 1957-1992: Masters & Johnson conduct laboratory studies
1915-2001
1894-1956 1925-

3. Sexual Response Cycle

4. The Psychobiology of Sex
Masters and Johnson (1966) describe the human sexual
response cycle as consisting of four phases:
Phase Physiological Response
Genitals become engorged with blood. Vagina
Excitement expands secretes lubricant. Penis enlarges.
Excitement peaks such as breathing, pulse and
Plateau blood pressure.
Contractions all over the body. Increase in
Orgasm breathing, pulse & blood pressure. Sexual release.
Engorged genitals release blood. Male goes
Resolution through refractory phase. Women resolve slower.

5. Female Orgasm
• Female orgasm (clitoral stimulation) versus
rest in heterosexual volunteers (N=12) during
PET scanning
Georgiais et al. (2006). European Journal of Neuroscience, 24, 3305-3316.

6. Female Orgasm
• PET scanning [15O]-H2O, subjective report of
orgasm, and rectal pressure monitoring
Georgiais et al. (2006). European Journal of Neuroscience, 24, 3305-3316.

7. Female Orgasm
„Le Petit Mort‟
• Areas Activated: motor cortex, cerebellum
• Areas De-activated: amygdala, prefrontal cortex
Georgiais et al. (2006). European Journal of Neuroscience, 24, 3305-3316.

8. Male Orgasm
• 12 heterosexual males experienced
orgasm while completing PET scanning
• Activated: cerebellum, thalamus, insula
• Deactivated: amygdala
Holstege et al. (2004) J Neuroscience, 23, 9185-9197.

9. Hormones and Sexual Behavior
Sex hormones effect the development of sexual
characteristics and (especially in animals)
activate sexual behavior.
Testosterone
Male Testes (Small amounts of
estrogen)
Ovaries Estrogen
Female (Small amounts of
Adrenals testosterone)

10. Estrogen
Female animals “in heat” express peak levels of
estradiol. Female receptivity may be heightened
with estradiol injections.
Sex hormones may have milder affects on
humans than on other animals.

11. Testosterone
Levels of testosterone vary somewhat in males
over a 24 hour period. Castration, which
reduces testosterone levels, lowers sexual
interest.

12. Testosterone & Age
Levels of testosterone vary somewhat in males
over a 24 hour period. Castration, which
reduces testosterone levels, lowers sexual
interest.

13. External Stimuli
It is common knowledge that men become
sexually aroused when browsing through erotic
material. However, women experience similar
heightened arousal under controlled conditions.

14. Imagined Stimuli
Our imagination in our brain can influence
sexual arousal and desire. People with spinal
cord injuries and no genital sensation can still
feel sexual desire.

15. Adolescent Sexuality
When individuals reach adolescence, their
sexual behavior develops. However, there are
cultural differences.
Sexual promiscuity in modern Western culture is much
greater than in Arab countries and other Asian
countries.

16. The Biopsychosocial Aspects of
Sex

17. Sexual Orientation
Sexual orientation refers to a person’s preference
for emotional and sexual relationships with
individuals of the same sex, the other sex, and/or
either sex.
Homosexual Heterosexual Bisexual

18. Sexual Orientation Statistics
In Europe and America, based on many national
surveys, homosexuality in men is 3.5% and in
women is 1.5%.
As members of a minority, homosexuals often struggle
with their sexual orientation (suicide/depression 3X).

19. Origins of Sexual Orientation
Homosexuality is more likely based on
biological factors like differing brain centers,
genetics, and parental hormone exposure rather
than environmental factors.

20. Neurobiological Basis of
Homosexuality?
• Levay compared the volume of the interstital
nuclei of the anterior hypothalamus (INAH)
• His sample (N=41) consisted of:
– 19 male homosexuals (19 AIDS+)
– 16 male heterosexuals (6 AIDS+)
– 6 female heterosexuals (1 AIDS+)
1943-
LeVay (1991). Science, 253, 1034-1037.

21. Animal Homosexuality (1500)
Mammals Birds Fish Insects
cat barn owl Amazon molly bedbug
chimpanzee chicken Bluegill sunfish blowfly
dog emu char cockroach
elephant King Penguin Jewel fish house fly
fox mallard Salmon Monarch butterfly
lion raven Ten-spined red ant
stickleback
raccoon seagull Three-spined Tsetse fly
stickleback
Bruce Bagemihl (1999) Biological Exuberance: Animal Homosexuality and Natural Diversity

22. Hypothalamus in Sheep
• 8% of rams mount males
• Rossi compared the sexually dimorphic
nucleus of females, males that prefer
females (MPF), males that prefer males
(MPM)
Females MPF MPM Females MPF MPM
Rossi et al. (2004). Endocrinology, 145, 478-483.

23. Hypothalamic Structure
• 8% of rams mount males
• Rossi compared the sexually dimorphic
nucleus of females, males that prefer
females (MPF), males that prefer males
(MPM)
Females MPF MPM Females MPF MPM
Rossi et al. (2004). Endocrinology, 145, 478-483.

24. Hypothalamic Function
• PET scans were completed while smelling androstadien
(AND) versus room air by young Heterosexual Women
(HeW), Homosexual Men (HoM), and Heterosexual Men
(HeM, N=12/group).
Savic et al. (2005). Proceedings of the National Academy of Sciences, 102, 7356-7361.

25. Hypothalamic Function
• PET scans were completed while smelling androstadien
(AND) versus room air by young Heterosexual Women
(HeW), Homosexual Men (HoM), and Heterosexual Men
(HeM, N=12/group).
Savic et al. (2005). Proceedings of the National Academy of Sciences, 102, 7356-7361.

26. Genes & Sexual Orientation
A number of reasons suggest that
homosexuality may be due to genetic factors.
1. Family: Homosexuality seems to run in families.
2. Twin studies: Homosexuality is more common in
identical twins than fraternal twins.
3. Fruit flies: Genetic engineers can genetically
manipulate females to act like males during
courtship and males to act like females.

27. Female-Female Behavior
• Male fruit flies have a fixed action pattern
courtship pattern
– Follow female -> Foreleg tap -> Sing song
• Fruitless gene is spliced in a sex specific pattern
• Females with male fru showed male behavior
• Videos
Demir & Dickson (2005). Cell, 121, 785-794.

28. Neurobehavioral
Differences
• Hetero and homo sexual men and women
(N = 35/group) completed a virtual water
maze.
Rahman & Andersson (2008) Hippocampus, 18, 55-63.

29. Sexual Orientation: Biology

30. Changing Attitudes

31. Contraception
1. Ignorance: Canadian teen girls do not have the
right ideas about birth control methods.
2. Guilt Related to Sexual Activity: Guilt reduces
sexual activity, but it also reduces the use of
contraceptives.
3. Minimal Communication: Many teenagers feel
uncomfortable discussing contraceptives.
4. Alcohol Use: Those who use alcohol prior to sex are
less likely to use contraceptives.
5. Mass Media: The media’s portrayal of unsafe
extramarital sex decreases the use of
contraceptives.

32. Sexual Problems
Men generally suffer from two kinds of sexual
problems: premature ejaculation and erectile
disorder.
Women may suffer from orgasmic disorders.
These problems are not due to personality disorders
and can be treated through behavior therapy and drugs.

33. Acquired Immune Deficiency
Syndrome
• Caused by Human Immunodeficiency Virus
• Transmitted via anal & vaginal sex, needles,
pregnancy/childbirth
• Worldwide (UNAIDS, 2009):
– 60.0 million infected
– 25 million dead
– 14 million orphaned children
1959-(1991)-

34. Summary
• Sexual Response Cycle
• Biopsychosocial factors
• Individual Differences in Orientation
– Genetic
– Endocrine
– Neurobiological
– Behavioral