Lecture 17 - Sex and Behavior PDF

12 Sex: Evolutionary, Hormonal, and Neural Bases Sex, Gender, and Sexual Behavior What determines one’s gender? (And what do we mean by “gender”?) Sex, Gender, and Sexual Behavior Two stories that illustrate this...

12 Sex: Evolutionary, Hormonal, and Neural Bases Sex, Gender, and Sexual Behavior What determines one’s gender? (And what do we mean by “gender”?) Sex, Gender, and Sexual Behavior Two stories that illustrate this complexity In 1965, male twins (Brian and Bruce) born in Canada At 8 months, twins were circumcised – Bruce’s circumcision was botched Penis burned and eventually fell off Family got involved with Dr. John Money at Johns Hopkins Bruce – sex reassignment surgery at age 22 months – raised as Brenda Story detailed in a Rolling Stone article and, later, a book Sex, Gender, and Sexual Behavior Money – major proponent that gender identity primarily determined by social learning in childhood Encouraged family to treat Brenda as a girl At puberty, Brenda given estrogens Money reported success with Brenda Sex, Gender, and Sexual Behavior Reality was far different Brenda – teased and bullied – engaged in stereotypically “masculine” or “boyish” behavior as a child At age 13, Brenda became suicidally depressed Learned the truth and, at 14, decided to live as a man – “David Reimer” Eventually  reverse assignment, married Committed suicide at age 38 Sex, Gender, and Sexual Behavior Story of David Reimer – altered how scientists view gender -- supported idea that early life (prenatal and infantile) hormones are important (though not entirely determinative) -- led to skepticism that genital reconstructive surgery was good idea for infants Sex, Gender, and Sexual Behavior Caster Semanya Sex, Gender, and Sexual Behavior Born and raised as a girl Began running and, eventually, made it to the Olympics However, people began questioning whether she was a woman Led to medical testing and eventually found she had much higher-than-normal levels of testosterone Sex, Gender, and Sexual Behavior Discovered  Semanya has 5-alpha reductase deficiency Has XY chromosomes Has undescended testes Has no uterus or fallopian tubes Has a shallow vagina Why? External genitalia requires conversion of testosterone to dihydrotestosterone (DHT) – 5 alpha reductase does this Sex, Gender, and Sexual Behavior Without 5-alpha reductase – no masculinization of external genitals Thus, at birth, family viewed her as a girl and she was raised that way She strongly identifies (and continues to identify) as a woman This example points to the complexity of sex and gender Sex, Gender, and Sexual Behavior Chapter 12 – will discuss biological psychology of: Sexual behavior, sexual differentiation, and diversity within these realms Reality is: We know far less about this topic than others – significant reluctance to study it (well, really, to fund it) Let’s start with what we know about BEHAVIOR 12 Sex: Evolutionary, Hormonal, and Neural Bases Sexual Behavior Sexual behavior, esp. in humans – highly diverse Neural circuitry of the brain regulates reproductive behavior – specific circuits identified in rodents Pheromones guide reproductive behavior in many species 12 Sex: Evolutionary, Hormonal, and Neural Bases Reproductive Behavior Can Be Divided into Four Stages 1. Sexual attraction 2. Appetitive behavior 3. Copulation 4. Postcopulatory behavior 12 Reproductive Behavior Can Be Divided into Four Stages Four stages of reproductive behavior: 1. Sexual attraction 2. Appetitive behavior 3. Copulation 4. Postcopulatory behavior Figure 12.1 Stages of Reproductive Behavior (Part 1) 12 Reproductive Behavior Can Be Divided into Four Stages Sexual attraction brings males and females together–may be synchronized with: Physiological readiness to reproduce, indicated by odors reflecting estrogen levels in females Learned associations, such as appearances 12 Reproductive Behavior Can Be Divided into Four Stages Appetitive behaviors establish, maintain, or promote sexual interaction. A proceptive female rat may approach males or perform “ear-wiggling.” Male behaviors include staying near the female, sniffing, singing, and nest-building (depending on the species) These are “species-specific” behaviors 12 Reproductive Behavior Can Be Divided into Four Stages Copulation involves one or more intromissions in which the male penis is inserted into the female vagina. Following stimulation the male ejaculates sperm-bearing semen into the female. 12 Reproductive Behavior Can Be Divided into Four Stages In rats  multiple separate intromissions prior to ejaculation – also necessary because repeated stimulation of cervix and vagina is necessary for brain to release hormones that support pregnancy Rats  also engage in multiple rounds of intromissions 12 Reproductive Behavior Can Be Divided into Four Stages After first copulation, a refractory phase follows–length varies with species – can be months The Coolidge effect refers to the faster resumption of mating behavior, with a different partner. If a female is willing to copulate, she is sexually receptive, or in estrus – most species  female only willing to mate if offspring are likely (e.g. around time of ovulation) 12 Reproductive Behavior Can Be Divided into Four Stages Postcopulatory behavior varies across species. In a copulatory lock, occurring in dogs and some mice, the penis swells temporarily and cannot be withdrawn from the female. Postcopulatory behavior may include parental behaviors to nurture offspring. 12 Reproductive Behavior Can Be Divided into Four Stages Internal fertilization takes place inside the female’s body. The fusion of gametes–sperm and ova–produces a zygote, or fertilized ovum. External fertilization takes place outside the female’s body, as with fishes and frogs that release gametes into water. 12 Reproductive Behavior Can Be Divided into Four Stages Learned a lot about rats’ reproductive behavior – let’s take a look at how that works 12 Reproductive Behavior Can Be Divided into Four Stages In rats, females ovulate, or release eggs, every 4–5 days. During estrus, a female will display proceptive behavior and adopt a posture called lordosis, allowing intromission. Figure 12.3 Copulation in Rats 12 Reproductive Behavior Can Be Divided into Four Stages In some rodents, pair bonds form between animals – live together before and long after copulation E.g. prairie voles HOWEVER, prairie voles may be socially monogamous but they are not quite sexually monogamous 12 Reproductive Behavior Can Be Divided into Four Stages Sex-steroid hormones are important in mating behaviors A castrated male rat  testosterone is no longer produced -- loses interest in mating Behavior is restored with testosterone treatment–the activational effect–hormones briefly activate behavior (Hormones can also have organizational effects that we’ll talk about later) Next graph – 3 male guinea pigs castrated Figure 12.4 Androgens Permit Male Copulatory Behavior 12 Reproductive Behavior Can Be Divided into Four Stages Note that the amount of testosterone did not determine copulatory score The guinea pigs just needed *enough* testosterone 12 Reproductive Behavior Can Be Divided into Four Stages Estrogens produced at the beginning of the ovulatory cycle are important for female proceptive behavior. Progesterone  more increases in proceptive behavior and make female receptive A female without ovaries will respond to a combination of estrogen and progesterone treatments  make her proceptive and receptive Figure 12.5 The Ovulatory Cycle of Rats 12 The Neural Circuitry of the Brain Regulates Reproductive Behavior In female rats, the ventromedial hypothalamus (VMH) is crucial to the lordosis response through steroid actions. Estrogen  increase in dendritic trees of neurons in the VMH Estrogen  production of progesterone receptors, which in turn contribute to lordosis through protein production. 12 The Neural Circuitry of the Brain Regulates Reproductive Behavior The VMH sends axons to the periaqueductal gray in the midbrain, which projects to the medullary reticular formation. This in turn projects to the spinal cord via the reticulospinal tract. As the male mounts, sensory information via the spinal cord evokes lordosis Figure 12.6B Neural Circuits for Reproduction in Rodents 12 The Neural Circuitry of the Brain Regulates Reproductive Behavior Note the interplay between hormonal stage, neural systems, and sensory information from male Now, let’s look at the male 12 The Neural Circuitry of the Brain Regulates Reproductive Behavior In male rats, the medial preoptic area (mPOA) coordinates male copulatory behavior The mPOA sends axons to the ventral midbrain, then to the basal ganglia to coordinate mounting Axons also project through brainstem nuclei to the spinal cord. 12 The Neural Circuitry of the Brain Regulates Reproductive Behavior Paragigantocellular nucleus (PGN)  normally inhibits the erection response–mPOA signals counteract the inhibition The vomeronasal organ (VMO) detects chemicals called pheromones, which activate male arousal VMO information is sent to the medial amygdala, and in turn to the mPOA Figure 12.6A Neural Circuits for Reproduction in Rodents 12 Pheromones Guide Reproductive Behavior in Many Species So, hormones and pheromones are key in determining sexual behavior in both males and females 12 The Hallmark of Human Sexual Behavior Is Diversity Humans differ from other species in reproductive behaviors – highly variable in sex-related behaviors Humans can report subjective reactions, such as orgasm. The four phases of response are excitement, plateau, orgasm, and resolution During the excitement phase, the phallus (penis in males, clitoris in females) becomes erect and there is increased blood flow to vagina, leading to production of lubricating fluid 12 The Hallmark of Human Sexual Behavior Is Diversity Men and women differ in sexual response: Women have a greater variety of responses, with three typical patterns Men, but not women, tend to have an absolute refractory phase following orgasm Figure 12.9 Human Sexual Response Cycles (Part 2) 12 The Hallmark of Human Sexual Behavior Is Diversity What happens in the human brain during sexual arousal? Next slide  shows activation of brain regions in men who viewed slides with images related to cocaine or sexual images HOWEVER  the slides were “unseen” cues – too fast to be aware of on a conscious level See activation of ventral striatum (nucleus accumbens), the amygdala, and the insula 12 The Hallmark of Human Sexual Behavior Is Diversity Orgasm in humans involves activation of a variety of brain structures, as indicated by fMRI E.g. amygdala, cingulate cortex, nucleus accumbens, hippocampus  also see activation of hypothalamic areas responsible for release of oxytocin, which occurs after orgasm fMRI activation of a woman having an orgasm 12 The Hallmark of Human Sexual Behavior Is Diversity Interestingly, women with spinal cord injuries in which sensory information from pelvic region cannot reach brain  can still have orgasms Evidence suggests that vagal nerve detects stimulation  leads to same activation of brain structures as seen in non-paralyzed women 12 The Hallmark of Human Sexual Behavior Is Diversity Much research devoted to understanding sexual behavior and differences between sexes (e.g., males have stronger sex drives than females on average) Problem: Research may describe differences but does not reveal source of differences – Socialization/culture? Biology? Combination? Moreover, differences between sexes are almost always smaller than differences WITHIN sexes 12 The Hallmark of Human Sexual Behavior Is Diversity Another possible problem in identifying differences between sexes: Very difficult to identify and rule out potential confounds Example: Evidence indicates women are more selective in choosing someone for potential romance Why? Evolution? Or something more mundane? 12 The Hallmark of Human Sexual Behavior Is Diversity What is the role of hormones in human sexual behavior? A low dose of androgens can stimulate interest and activity in males who do not increase testosterone at puberty  as with rats, additional testosterone does not do anything  No correlation between androgen levels and sexual activity in a man 12 The Hallmark of Human Sexual Behavior Is Diversity In some women, estrogens and androgens may be beneficial to postmenopausal women  most research, though, has not identified easy “fix” for pre-menopausal women with low sexual interest  A LOT of mixed results – and a lot of potential confounds 12 The Hallmark of Human Sexual Behavior Is Diversity Pheromones and humans Pheromones may affect human reproductive behaviors–menstrual cycles of women living together may synchronize The major histocompatibility complex (MHC) is a group of immune-related genes with many alleles Women prefer the smell of men with MHCs not too similar or dissimilar to their own