CHAPTER 7

1. CHAPTER 7 The Biology of Sex and Gender Sex as a Form of Motivation

2. Sex as a Form of Motivation • Sex = motivated behavior • Similar to hunger, thirst, aggression • Includes maternal/parenting behaviors as well as mating • Unusual in that doesn’t fit homeostatic model of other “motivated” behaviors • Has similar stages to other motivated behavior • Arousal • Satiation • Involves hormones • Controlled by specific brain areas

3. Sex as a Form of Motivation • William Masters and Virginia Johnson • 1960’s body of work • groundbreaking research on human sexual response. • Identified four phases of sexual response: • The excitement phase is a period of arousal and preparation for intercourse. • During the plateau phase, the increase in sexual arousal levels off. • During orgasm, rhythmic contractions occur in the vagina and those in the penis are accompanied by ejaculation. • Resolution follows as arousal decreases and the body returns to its previous state.

5. Excitement phase • Period of arousal and preparation for intercourse • Autonomic arousal • Increased heart rate and increased respiration • Increased blood pressure and muscle tension • Females (human) • Clitoris becomes erect • Vaginal lips swell; vagina lubricates • Breasts enlarge; nipples erect • Men • Penis engorged, erect • Nipples erect • Animals: lordosis • Rearing and presenting • Elevated rump • Move tail to side

6. Excitement phase • Influenced by opportunity and sexual stimuli rather than time • Many cues innate • But many cues are learned • Some animals: sexual arousal is regulated event triggered by season, hormones, time • In humans: reflexive- respond to environmental cues • Humans respond to many stimuli, but particularly learned stimuli • Some animals are reflexive ovulators (many rodents) • Thankfully, humans are NOT!

7. Plateau phase and Orgasm • Increase in sexual arousal levels off • Arousal maintained at high level for minutes (or seconds) • Physiological changes: • Testes rise in scrotum in preparation for ejaculation • Vaginal lubrication increases, vaginal entrance tightens • At orgasm: • Rhythmic contractions to penis; ejaculation • Vaginal contractions as well • Help push sperm up vaginal canal

8. Resolution phase • Arousal decreases • Body returns to pre-arousal state • Males have a refractory phase, • unable to become aroused or have another orgasm for minutes, hours, or even days, • Highly dependent on the individual and circumstances. • The Coolidge effect is a quicker return to sexual arousal when a new partner is introduced.

9. Role of Testosterone • Testosterone is the major sex hormone in males. • Also necessary for women • Ratio of estrogen/testosterone is critical • Castration • removal of the gonads (testes or ovaries) • technique used to study hormonal effects • removes the major source of sex hormones. • Castration results in a loss of sexual motivation in nonhuman mammals of both sexes. • Androgens: class of hormones responsible for a number of male characteristics and functions.

10. Role of Testosterone • Hormones become less important in human behavior • Still are necessary • But of equal importance becomes experience and stimuli factors • In humans: castration only results in loss of sexual behavior if occurs prior to puberty • Sexually experienced men may experience changes in sexual behavior • Not LOSE sexual behavior • Appears testosterone may be stimulated by sexual activity in humans • Testosterone levels high in men at END of period in which intercourse occurred, not before • Anticipation of sexual activity may increase testosterone • Thus: effect of depo-provera for sexual offenders not necessarily effective

11. Role of estrogen • In most species, females only engage in sexual behavior during estrus, or heat • Humans and many primates are sexually active throughout cycle • Estrus: • period when the female is ovulating; sex hormone level are high • In animals: said to be in heat. • Humans do not have clear “estrus”, al • data suggest that women more likely to initiate sex when ovulating • Estrogen : • class of hormones responsible for a number of female characteristics and functions • Testosterone also peaks with estrogen during ovulation/mid cycle • Older women have lower levels of testosterone, estrogen • Testosterone increases in women with increase in sexual activity • May be testosterone which producing increase in sexual behavior during ovulation

12. Sex and the brain • Medial Preoptic Area(MPOA) of the hypothalamus • Modulates both male and female sexual behavior. • Stimulation of the MPOA increases copulation in rats of both sexes. • The MPOA is active when rats copulate spontaneously. • The MPOA is responsible for performance rather than sexual motivation. • Lesions effects: alters form of behavior • male monkeys no longer tried to copulate, • Instead would masturbate in the presence of a female.

13. Sex and the brain • Medial amygdala • Located near lateral ventricle in temporal lobe • Stimulation releases DA signals to MPOA • contributes to sexual behavior in rats of both sexes. • role = respond to sexually exciting stimuli • Appear to be some “innate” stimuli • Probably lordosis • In lower primates: strong visual stimuli: • Swelling of female’s genitals • Color change in genitals when in estrous- their “sex skin” • In humans: breasts, buttocks, learned stimuli

14. Sex and the brain • Sexually dimorphic nucleus (SDN) • located in the MPOA. • More significant for males • Why name? The SDN is five times larger in male rats than in females. • Destruction of SDN reduces sexual activity • SDN connects to other brain areas: • Integrates sensory and hormone information • Coordinates behavioral and physiological responses to sexual cues • The level of sexual activity in males related to SDN size • SDN size depends on prenatal (before birth) exposure to testosterone. • Suggests in-utero environment may be critical factor in sexual behavior

15. a. Adult male b. Adult female • The SDN is larger in the male than (b) the SDN in the female (b). • (c) The effects of two masculinizing hormones on the female SDN. SDN-POA c. Adult female exposed to testosterone diethystilbesterol SDN-POA

16. Sex and the brain • Ventromedial nucleus of the hypothalamus • important for sexual behavior in female rats. • Activity increases there during copulation • destruction reduces the female’s responsiveness to a male’s advances. • Also important for maternal behaviors • Nursing • Caretaking • Less is known about female sexual response

17. Sex neurotransmitters • Dopamine (DA) • Injection and microdialysis studies show importance • DA activity in MPOA involved in sexual motivation • Both for males and females of several species • Critical for sexual performance in males. • Small amounts of DA stimulate D1 receptors • This activates parasympathetic NS • Increases motivation, erection, delays ejaculation • As DA increases- stimulated D2 receptors • Shifts autonomic balance to sympathetic NS • Inhibits erection • Elicits sexual refractory period

18. Sex neurotransmitters • DA changes parallels sexual behavior during Coolidge effect • Increases in male rat’s nucleus accumbens in presence of female • Drops to baseline as interest wanes • Increases with new female • Remember role of DA as a signal for reward- this fits the pattern • Suggests that DA reflects male’s interest level, not result of sexual activity • DA is motivator for sexual (and other behaviors); not the reinforcer!

19. Sex neurotransmitters • Ejaculation elicits serotonin increases in the lateral hypothalamus • This contributes further to the refractory period. • If inject 5HT reuptake blocker into lateral hypothalamus: • Longer time until male rat attempts copulation • Inhibits ability to ejaculate when do copulate • Helps explain sexual side effects of SSRIs • These drugs are 5HT reuptake blockers • Essentially, are remediating depression • But also prolonging refractory period, • Make it more difficult to become aroused

20. Sex neurotransmitters • Oxytocin • hormone that causes smooth muscle contractions • Involved in vaginal contractions, ejaculatory mechanisms • Critical for ejection in lactating (breast feeding) females. • Also important for childbirth- starts labor • is released as a neurotransmitter by hypothalamic neurons. • in non-human animals: • contributes to male sexual behavior • Contributes to female receptivity • appears to account for monogamous pair bonding in prairie voles. • In humans: • Increases dramatically during masturbation • Involved in subjective arousal, feelings of pleasure during orgasm

21. pheramones • Pheramones: • Airborne hormones • Released in presence of another “animal”- particularly of opposite sex • Preti, et al., 1998: study on pheromonal effects in humans • Synchrony of women’s menstrual cycles most likely due to pheromones • women exposed to pheramones from each other= more synchronized in menstrual cycle • When exposed to male pheramones: menstrual cycles = more regular • Pheramones appear to alter release of lutenizing hormone, critical for menstrual cycle • Why? For a “troop” of primates, more easily impregnated if all ovulate at same time.

22. pheramones • May also enhance sexual attractiveness in human s • Individuals w/perfume/aftershave with pheramones judged more attractive • Not particularly strong effect: human’s vomeronasal system is very small • Tend to use color signals, other signals more • Boar’s Mate is cheaper!

23. Olfactory system • Olfaction = chemical sense (responds to chemical stimulation) • Airborne odorous materials enter nasal cavity • Dissolve in mucous layer overlapping receptor cells • Odorous particles then stimulate receptor cells when contact with receptor site on cell dendrites • Axons from olfactory receptors pass through opening in base of skull to enter olfactory bulb • Olfactory bulb overlies nasal cavity • Neurons follow olfactory nerve to olfactory cortex • Olfactory cortex in inner folds of temporal lobe • In other animals: is separate cortex area • Humans can distinguish approximately 10,0000 odors • Between 500-750 different receptors • Only ¼ to ¾ are functional • Brain identifies odor by combination of stimulation

24. Stimulus factors • Each animal has unique genetically determined odor • Mothers/babies identify one another from birth • Families can identify eachother’s smell • Important in sexual arousal • Pheromones • airborne chemicals released by an animal • have physiological or behavioral effects on another animal of the same species. • Pheromones are detected by the VNO (vomeronasal organ), a cluster of receptors located in the nasal cavity.

25. Stimulus factors in sexual attraction • Evidence that odor influences mate choice • May be to avoid genetic inbreeding • Women rated men’s smells as more pleasant when men had greater difference in major histocompatability complex (MHC) than the women raters • MHC contributes to autoimmune function • Many animals “scent mark” • Your cat has glands just above eyes • When animal rubs/pees, etc. is scent marking • Marking territory, leaving scent around • Fire hydrants = doggie facebook!

26. The Biological Determination of Sex • Sex • term for the biological characteristics that divide humans and other animals into the categories of male and female. • Typically male or female • Gender: behavioral characteristics associated with being male or female. • Gender role: set of behaviors society considers appropriate for people of a given biological sex. • Gender identity: aperson’s subjective feeling of being male or female.

27. Chromosomes and hormones • We typically start out as XX or XY • XX = female • XY = male • Are exceptions • Developing gonads: undifferentiated at first • 8-12 weeks begin to develop internal, then external genitalia • For the first month, XX and XY fetuses are identical and essentially female. • Later, primitive gonads develop into appropriate primary reproductive organ: • XY = male = testes • XX = female = ovaries • Several syndromes associated with sex chromosomes: • Turner’s syndrome: XO • XYY syndrome

28. Becoming a female • The default sex: what happens if no testosterone burst • Müllerian ducts : develop into • Uterus • fallopian tubes • inner vagina. • Wolffian ducts that would become the male organs wither and are absorbed. • The undifferentiated external genitals become • clitoris, • outer segment of the vagina, • the labia, which partially enclose the entrance to the vagina.

29. Becoming male • Receive Y chromosome from the father • SRY gene on that chromosome causes the primitive gonads to develop into testes • The testes begin secreting two types of hormones: • Müllerian inhibiting hormone defeminizes the fetus by causing the Müllerian ducts to degenerate. • Testosterone, the most prominent of the androgens, masculinizes the internal organs. • The Wolffian ducts must be turned ON • develop into the seminal vesicles: stores semen, • Also the vas deferens: carries semen from the testes to the penis. • A derivative of testosterone, dihydrotestosterone, masculinizes the external genitals.

31. Brain and hormones • Sexual development at puberty • Average age of menarche for girls: 10.5-12 years • Average age for boys: 12.5-14 • Begin development of secondary sex characteristics • Females: breasts, pubic hair, widening of hips, voice changes, onset of menses • Males: voice changes, widening of shoulders, pubic hair, lengthening of penis • Why earlier than previous generations? • Hormones in food supply • Better diet • What triggers puberty? • Still unknown • Family history • Hypothalamus critical

32. Brain and hormones • Preoptic area of Hypothalamus: POA • At puberty, begins to secrete gonadotrophin=releasing factor: GRF • Carried by bloodstream to anterior pituitary • At anterior pituitary: encourages release of LH and FSH (follicle stimulating hormone) • Effect is: • Flood of release of estrogen from ovaries • Flood of release of testosterone from testes • Result = maturation of primary sexual organs and development of secondary sex characteristics

33. Brain and hormones • The presence of testosterone masculinizes certain brain structures. • Actually, is estradiol plus testosterone • a derivative of estrogen • the principle estrogen hormone, that carries out the final step of masculinization. • When testosterone enters the neurons it is converted to estradiol by a chemical process called aromatization. • During critical period for brain masculinization:aromataseincreases in the areas that are to be masculinized.

34. Organizing and activating effects • Organizing effects • mostly occur prenatally and shortly after birth. • They affect structure and are lifelong in nature. • Activating effects • can occur at any time in the individual’s life • may come and go with hormonal fluctuations • or be long lasting, • are reversible. • Helps explain some gender differences

35. Hormones responsible for Cognitive Differences? • Masculinization of prenatal brain: Birds and Birdsong • Bird songs generally fall into 2 classes • Male calls designed to attract females • Territorial calls designed to warn away competitor males • Most females have limited song range • In birds: specialized circuitry for song • Provides nice opportunity for studying sexual development • Can study Sexual maturation • Nature/nurture effects

36. Hormones responsible for Cognitive Differences? • Finches: • Male learns song by listening to father/nearby males • Amount of singing dependent on testosterone levels • More testosterone = more singing • Castrated birds do not sing • Can make female sing if give high doses of testosterone • Activational effect • Need sexual circuitry • Need exposure to correct cues and experience • Must develop circuits at birth • Must turn on circuits at puberty • What does this mean? Need nature AND nurture to take on adult male role.

37. Gender-Related Behavioral and Cognitive Differences • Eleanor Maccoby and Carol Jacklin, 1974 • reviewed over 2,000 studies that included measures of sex differences. • They concluded that the evidence firmly supported three differences in cognitive performance and one difference in social behavior: • Documented gender differences: • Girls have greater verbal ability than boys. • Boys excel in visual-spatial ability. • Boys excel in mathematical ability. • Boys are more aggressive than girls. • Why? The great unknown • Nature? • Nurture?

38. Gender-Related Behavioral and Cognitive Differences • More recent data show reducing gender gap- or reversal of gender gap! • Cognitive differences = rather limited • Females higher in verbal fluency and writing • No difference in in reading comprehension or vocabulary. • Male scores higher than females’ on most on tasks requiring • mental rotation of a three-dimensional object and • But not on other spatial tasks.\ • Females are better at computation • Males do better on standardized tests of broad mathematical ability (e.g., ACT, SAT) • More women go to college, graduate from college • Is this nature or nurture?

39. The Biological Determination of Sex • Sex • term for the biological characteristics that divide humans and other animals into the categories of male and female. • Typically male or female • Gender: behavioral characteristics associated with being male or female. • Gender role: set of behaviors society considers appropriate for people of a given biological sex. • Gender identity: aperson’s subjective feeling of being male or female. • Not always clear cut!

40. Sexual Anomalies • Pseudohermaphrodites • ambiguous internal and external organs • gonads are consistent with their chromosomes • Occurs when internal and external genitalia do not match. • Several kinds of pseudohermaphrodite syndromes • Male to female: Deficiency in testosterone converting enzyme • Male to female: 5a-reductase syndrome • Male to female: Androgen insensitivity syndrome • Female to Male: congenital adrenal hyperplasia (CAH)

41. Male Sexual Anomalies: Testosterone Converting deficiency • Deficiency in testosterone converting enzyme • 17a-hydroxysteroid: converts testosterone into dihydrotestosterone • Normally: Dihydrotestosteronemasculinizes external genitalia before birth • This does NOT occur for these individuals • Internal development is male: testes • External development is female: vagina, labia • Get normal surge of testosterone at puberty, which elicits secondary male sex characteristics- beard growth, deepening voice (no breasts)

42. Male Sexual Anomalies:5a-Reductase syndrome 5a-reductase syndrome Genetic defect; common with severe inbreeding Large population of 5a-reductase individuals in Dominican Republic Have external female genitalia, but testes Are reared as girls from birth At puberty, switch gender to male Interesting because of societal/cultural effects

43. AndrogenousSexual Anomalies • Androgen insensitivity syndrome, • Another form of male pseudohermaphroditism • caused by a genetic absence of androgen receptors which results in insensitivity to androgen. • Ovary development suppressed by Müllerian activation • This inhibits development of gonads into ovaries • BUT: Individual is unaffected by androgens • Thus testes also do not descend or develop • external genitals develop as more or less feminine. • In the absence of testosterone’s influence: • end to have well-developed breasts • flawless complexion • Vagina ends in blind pouch- no cervix or uterus • Generally reared as woman • May need estrogen therapy • Often identified at puberty or when can’t get pregnant

44. Female Sexual Anomalies: Congenital adrenal hyperplasia • Congenital Adrenal Hyperplasia (CAH) • results from an enzyme defect • Individual’s adrenal glands produce large amounts of androgen during fetal development and after birth until the problem is treated. • Result: masculinization of external but not internalgenitalia • Internally female • Externally male • Parents often choose reconstructive surgery • reduce the size of the clitoris • eliminate labial fusion • Gives genitals a more feminine appearance. • If masculinization is more pronounced, the parents may decide to rear the child as a boy. • Surgeons finish closing the labia • insert artificial testes in the scrotum to enhance the masculine appearance.

45. Brain changes with Sexual Anomalies • Reversing the sex hormone balance during prenatal development changes the brain and later behavior in nonhuman animals. • Women born with CAH: described as tomboyish in childhood. • Androgen-insensitive males: • typically feminine in behavior • have a strong childbearing urge • decidedly female in their sexual orientation. • Androgen insensitive males are like females: • verbal ability is higher than their spatial performance • spatial performance is lower than that of other males. • CAH women more like men • show higher spatial ability than other women, • even draw pictures more typical of boys, • using darker colors • including mechanical objects • excluding people.

46. Are you sex-assigned at birth? • The “neutral-at-birth” theorists: • claim individuals reared in opposition to their chromosomal sex generally accept their sex of rearing • his demonstrates that rearing has more effect of gender role behavior than chromosomes or hormones. • Sexuality at birth hypothesis: Milton Diamond: • reason individuals with ambiguous genitals accept their assigned gender is that sex of rearing is usually decided by whether the genital appearance is predominantly masculine or feminine, • This typically reflects the prenatal hormone environment. • According to Diamond: no case in the literature where an unambiguously male or female individual was successfully reared in opposition to the biological sex.

47. Sexual Orientation • How many genders? • Anne Fausto-Sterling suggests at least five sexual categories • Male • Female • Three Intersexes: Merm, Ferm and Herm • Homosexuality: preference for own sex/gender • Bisexual: those who are not exclusively homosexual or heterosexual • Gender Nonconformity • a tendency to engage in activities usually preferred by the other sex • typical preference for other-sex playmates and companions while growing up. • During development homosexuals and transsexuals do show a high rate of gender nonconformity • Difference between trans-sexual and trans gender • Trans-sexual is a pseudohermaphrodite • Trans-gender is individual who “feels” or identifies with other gender • May be due to brain masculinization/feminization as well as effects on gonads

48. Sexual Orientation • Genetic studies provide the most documented and most consistent evidence for a biological basis for sexual orientation. • Homosexuality is 2 to 7 times higher among the siblings of homosexuals than it is in the population. • Identical twins are more concordant for homosexuality than fraternal twins or non-twin siblings. • Evidence of homosexual behavior in animals; not exclusively a “human” behavior • Usually occurs when low resources or overpopulation • Also occurs during pubescent play behavior

49. Sexual Orientation and brain differences? • INAH3 (third interstitial nucleus of the anterior hypothalamus) • Simon LeVay (1991) • INAH3 is half the size in gay men and heterosexual women compared to heterosexual men. • Criticism: only looked at (dead) gay men in 1980’s: why important? • suprachiasmatic nucleus (SCN) • Has found to be larger in gay men than in heterosexual men • contained almost twice as many cells that secrete the hormone vasopressin. • Anterior commissure: • larger in gay men and heterosexual women than in heterosexual men • Involved in dual-processing across hemispheres • May explain some gender differences.

50. Figure 7.17 INAH 3 in a heterosexual man (left) and a homosexual (right)