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Introduction to Brain and Behavior [NOTES] Part 12 -- I got a 92% in the course

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PSB 2000
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Sexual Development  Sex hormones • Classes of sex hormones  Organizational effects of hormones • Reproductive organs, Brain, Behavior  Activational effects of hormones • Reproductive behavior, Menstrual cycle  Sex hormones • Steroid hormones • Sex hormones are released mostly by gonads (ovaries and testes), and to a lesser extent by adrenal glands • Affect brain, genitals, and other organs • Classes: → Androgens (Testosterone, DHT)  mostly males → Estrogens (Estradiol) mostly female → Progestins (Progesterone)  mostly female  Organizing effects vs. activating effects of sex hormones • Organizing → Occur mostly during sensitive periods in development (well before birth in humans) → Effects are generally permanent → Determine whether brain and body will develop male or female characteristics • Activating → Occur any time in life, when a hormone temporarily activates a response (physiological or behavioral) → Effects last as long as hormone is present…thus generally temporary → Includes menstrual cycle in women, sexual excitement in men (and in women… there is some data…)  How do hormones affect behavior? • Alter activity in certain brain regions  change the way the brain responds to certain stimuli → A few examples ⇒ T and probably E decrease pain and anxiety ⇒ Decreases in T and E associated with memory problems ⇒ E stimulates growth of dendritic spines in hippocampus ⇒ E increases production of dopamine and serotonin receptors in NA, PFC, olfactory cortex, and other cortical regions → In terms of sexual behavior, hormones change activity in some brain regions and change sensitivity of penis, vagina, and cervix  Development of male or female reproductive tracts • Default is female; presence of the SRY gene signals male development • SRY gene is turned on  gonads begin to develop as testes  testes secrete anti- mullerian hormone to cause regression of mullerian ducts and testosterone to promote development of Wolffian ducts • No SRY gene  regression of Wolffian ducts; development of mullerian ducts  female  Feminization/demasculinization of genetic male • The “default” development pattern is female • w/o androgens or the ability to respond to androgens (androgen receptors), the individual develops as a female • SO, things that block androgen activity during a critical period of development can be feminizing/demasculinizing in a genetic male → Castration → Lack of androgen receptors → Drugs that block effects of testosterone (including marijuana, alcohol, haloperidol, and cocaine) • To a much lesser extent, estrogens (including environmental estrogens) can alter the male pattern of development → Prostate gland (which stores sperm and releases it during intercourse) is especially vulnerable  Sexual differentiation in hypothalamus • Testosterone during sensitive/critical period will masculinize the hypothalamus of genetic females • Males and females masculinized with T have larger sexually dimorphic nucleus (in preoptic area; much larger in males due to growth in neurons because of high levels of testosterone) • Also, female hypothalamus generates cyclic pattern of hormone release (causing menstrual cycle). Male hypothalamus and masculinized female hypothalamus do not. • Behavior is also masculinized… if masculinized, female is given T again as an adult  Sex differences in the brain • Parts of the brain larger in males: → Especially white matter, Corpus callosum, Small part of prefrontal cortex • Parts of the brain larger in females: → Other areas of prefrontal cortex, Motor cortex, Portions of emotions, Occipital lobe good for visual processing • Sex differences in the cerebral cortex and cognition → Men tend to have more white matter than women, Women tend to have more neurons in language area in temporal lobe → Men outperform women in some visuospatial tasks ⇒ Mental rotation of 3-dimensional objects, Throwing accuracy, Navigation or route finding → Females outperform males in other visuospatial tasks ⇒ Route finding with landmarks, Memorization of location of objects, Rapid and fine manipulation of objects  Those were the organizational effects • Development of reproductive tracts and external genetalia, Differences in the hypothalamus and other regions of the brain, Differences in cognition  Men • Sexual excitement highest when T is highest (15-25 yrs. Old) → Higher T levels  more “partner-seeking” even if married → Decrease T  decrease sexual activity → Decrease T to control sex offenders ⇒ But T alone doesn’t cause these behaviors ⇒ Sex offenders have average T levels, except child molesters whose T levels are especially high • Fun fact: Viagra works by prolonging effects of nitric oxide (NO) → T increases release of NO → NO facilitates hypothalamus neurons important for sexual behavior and increases blood flow to penis  Women • Hypothalamus + pituitary + ovaries = menstrual cycle → Depends on 4 hormones ⇒ From anterior pituitary: luteinizing hormone (LH) and follicle-stimulating hormone (FSH) ⇒ From ovaries: estrogen and progesterone • Certain behavioral changes when periovulatory → Periovulatory means that E is high, P is beginning to rise, T is as high as it gets in females; this is the few days surrounding ovulation → More likely to initiate sexual behavior, Find erotica more pleasant and arousing → For a “short-term sexual relationship”, prefer more masculine looking men and men who seem “athletic, competitive, and assertive, and who did not describe self as having a nice personality” → Lap dancers earn the most tips during this time (b/c they feel/act sexier?)  Oxytocin • Released from posterior pituitary • Stimulates uterine contractions during and after delivery of baby • Stimulates mammary glands to release milk • Released by sexual pleasure, especially orgasm • Decreased anxiety after orgasm due to oxytocin → Could also be the source of reported anxiolytic effect of breastfeeding as well • Important in pair bonds between mating partners • Important in pair bonds between mother and infant  Hormones and parental behavior • E, prolactin (milk production, gathering wandering young) oxytocin prime mother before birth • Hormone receptors also change their expression patter during pregnancy to prepare for motherhood → Increase in areas important for maternal behavior; decrease in areas important for sexual behavior…go figure! • In moms, experience is important too, and eventually parental behavior is accomplished by experience without the need for additional hormones → This is in rodents; in humans, hormone priming isn’t even needed • Vasopressin: important in paternal behavior → Male prairie voles have high VP levels and pair bond with female and help rear young (so considered “monogamous”) → Male meadow voles have low VP levels, and ignore female after mating (so considered “promiscuous”) ⇒ Unless you genetically engineer them to make more VP, in which case they become monogamous  Differences in sexual behavior • b/t males and females → number of partners, what is sought in a mate, importance of olfaction, psychological components: jealousy, trending differences in sexual orientation • w/I sexes → heterosexual, bisexual, homosexual • Sexual terminology → Gender (more to how you identify) versus sex (chromosomal, physical) → Gender identity versus sexual orientation → Categorical vs. continuous ⇒ Sexual orientation is mor
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