15. Human Sexual Behavior I

[Music] Stanford University is this on yes well congratulations everybody has survived the midterm uh including the TA so far who recently have been let out of their inment with thousands of pages of uh exam Pages uh so those are rolling along and everybody is still awake so that's good okay so we have now officially entered the second Half of the course and organizational things uh readings will now be read hopefully okay so that's not useful um books books now is a good time to actually go and start reading those books uh and again if you

are not up to all of both of them some recommended chapters have come along and pay attention to those and again a subset of you you may not know it yet but about 25% of you will have your life transformed by that chaos book whereas 25% will resent the purchase price and by forcing you to do this also another major major transition here which is as far as I can tell so far I have run out of steam turning the extended notes into actual expository writing so they're just going to take the form of really

poorly organized outline mind and so that happens okay what else what we now transition to is going to be our strategy for the rest of our course which is to look at various subjects and Coming down the pike after the lectures today and Friday on sexual behavior will be aggression competition cooperation empathy uh potentially language use schizophrenia somewhere in there there's going to be a week or so on that chaos stuff but for all of these subjects we are now going to follow the general strategy we will start off looking at what the behavior is

and what we're going to try to do there in addition to looking at in lots of different species Is to be as objective as any good old ethologist in considering the fixed action patterns of a particular behavior that established with the promise that in lots of cases what we think comprise some of these behaviors turn out not to be the case that established what we will start is our inexorable March to the left the timeline that constitutes everything we learn now stepping back and saying okay one millisecond before that behavior occurred what was going on

In the brain what parts of the brain what neurotransmitters all of that stepping back before that a second before a minute before whatever what was it in the environment that triggered the brain to produce that behavior what was the acute releasing stimulus stepping back what do hormone levels that hour that day some such time span of that what acute hormonal exposure had to do with sensitizing you to the Environmental stimulus which released the nervous system into generating Behavior marching all the way back throwing in cultures someplace or other perinatal effects early developmental hormonal stuff eventually

considering what do the genetics of the individual of the population of the species Evolution kicking in there someplace or other what do all of these things and something having to do with ecology thrown in there just for good measure Working our way back in each of these cases understanding what was the biology of 1 second before one minute one hour one million years before that gave rise to it back to our two major themes from day one we are now about to be Unbound found unfettered by our buckets our categorical buckets and instead explore their

interactions the other being that notion from the very first class which is at any given point if we're talking about chronic hormonal effects on this Behavior what we're talking about is the way those hormone patterns were shaped during this period the way genes contributed to the enzymes that make the hormones The receptors the second you're talking about genetics all of this is becoming Apparent at every one of these points whatever point we are talking about is going to be the end product of everything to the left and just a temporary sort of footing before going

to the things on the right so this will Be our strategy Forever After now so we start off doing this with looking at sexual behavior the neurobiology the endocrinology and the early experience etc etc so to inaugurate the second half of the course and the fact that it's starting off with lectures on sexual behavior it has to start off with a stupid obligatory sex joke okay so the Martians come to Earth and they turn out to be great guys they're really terrific they get along wonderfully with Earthlings all of them like each other a lot

they're all becoming great friends they pass their hours learning about each other's planets what's the weather like there what are sports like here what are recipes everybody's getting along to L and eventually the earthlings and the Martians are getting along well enough that they get around to asking the question that everybody's really interested in which is well how do you folks go about Reproducing so the decision is made the Martians are going to go first so they clear out a big space and a whole bunch of martians come in there and they stand on top

of each other's heads and their noses flash different colors and steam comes out of various orifices and there's clanking noises and whatever and out pops a new little Maran and the earthlings say wow that was great and love the concept and I got great video of that and that's terrific all of that Okay so that's worked out and now it's the humans turn so a willing couple is found and some space is cleared out and the Martians sit down there with their video cameras as well and clicking away and this couple goes at it and

they finish the whole thing in a sweaty mess at the end and the Martians say that's wonderful that's so interesting you earthlings are just and the fascinating things you do but we have one question though and which is so where's the new Human and he said oh that takes nine months they said well why were they in such a rush at the end so our first question here is uh why were they in such a rush at the end okay three possible answers Choice number one vote for it why were they in such a rush

at the end number one because they were acting with this fervent desire to do something for the good of the species just seeing if any hands go up that's a good thing option number two Doing that because you want to maximize the number of copies of your jeans passed on to the next Generation option number three because it feels good okay one hand goes up and I'm not sure what that indicates about everyone but I will uh remind you from the survey in the first class there that a far greater percentage of you want to

learn about depression than about sexual behaviors so there you have it with the Stanford Experience okay because it feels good and what we deal with here right off the start is this important dichotomy between proximal and distal explanations for Behavior explanation a distal explanation for sexual behavior parentheses why were they in such a rush at the end passing on copies of your genes the effects of hormones and certain reward Pathways in the brain all of that proximal mechanism being that it feels good and starting off right off The bat the thing to make sense of

with sexual behavior is it is driven by this amazing little Loop here of sensory stimuli and feedback and immediate Sensations that drive the Behavior coming out and all this stuff down here is for the doctoral thesis somewhere down the line that's not what the motivation is probably more than any other of the behaviors we will look at the driving forces are very proxim ones nobody sits there and figures out how Many copies of genes they are passing on and thus are willing to speed up to produce a new human 9 months later it instead in

species after species it is proximal motivating mechanisms for generating the behaviors okay so beginning to look at the actual behaviors there is a funny Duality to making sense of sexual behavior across different species a funny sort of contrast the first one being that well all species go about sex or all Vertebrate species go about sex in a roughly similar way yet you don't want it to be too similar to the species next door there's an interesting sort of dichotomy there all sorts of vertebrate species are doing things with pelvic thrusting and orgasms and pay stay

tuned that's coming and ejaculation and lordotic reflexes and things of that sort highly conserved fixed action patterns across lots and lots of different species nonetheless amid that You've got this other problem which is you want to have these fixed action patterns being specific to your species you do not want to mess up so there's this strange simultaneity of very very conserved basic building blocks of the fixed action patterns of sexual behavior but along with that a lot of selectivity within species now how does that selectivity begin to work what you get is this very interesting

interplay this intercalation between the releasing Stimuli and the fixed action patterns what you get is this chaining of behavior in other words the fixed action pattern of one of the individuals constitutes the releasing stimulus for the other individual's fixed action pattern which constitutes the releasing stimulus for this individual's fixed action pattern this chaining of transitions there of interplay between these two which is where you get the species specificity from okay so in Terms of making sense of that of course any of this in terms of looking at the general features of how to think about

sexual behavior across species of course what you have to have out the Woo is your basic ethology Credo of interviewing an animal in its own language about its sexual behavior wonderfully summarized in this quote by Martha mclintoch researcher I think I've used this quote already which is in her particular case studying female rat Sexual behavior which turns out to be this very ornate process involving a lot of running around on the part of the female studying female rat sexual behavior in a cage is like trying to study swimming behavior of a dolphin in a bathtub

you need to get it in the natural setting or else you are going to lose all sorts of insight in the particular realm of female rat sexual behavior the standard picture for decades and decades the centuries where Our finest Minds have looked at rats having sex the standard Dogma has been that the female role is a very passive receptive one and it turns out it's a very passive receptive one if she doesn't have enough room to run around and do all sorts of cording stuff on her own all sorts of proceptive sexual behaviors which you

can't see if you're studying an animal in a setting where they can't speak in their own language so a big big sort of vote for eth olical Principles when it comes to this all right so just to get some jargon under our belt right from the start here in terms of how the professionals talk about sex when they're talking about sex and trying to sound like professionals here are some of the terms old outdated term Freudian term that nonetheless has entered the general sort of no world of referring to sexual arousal and motivation libido libido

as we will see that commonplace everyday usage term Uh is perhaps more technically described as horniness but can also be described as one term within a trio of the terms that people in the business really use most frequently attractivity proceptivity and receptivity quick get to work on poems about those three terms but what you've got here is attractivity how attractive an individual is to someone else receptivity how recept that individual is to the interest of the other Individual proceptivity the active behaviors that are carried out in response to being attracted to and thus you could

say because of the attractiveness of this organism this other organism began proceptive behaviors which did or did not prove to meet with receptive fixed action patterns and responses the very words any of us would use to describe what goes on at a party Okay so we've got that Triad there the terms that are much More in common than terms like libido or arousal or motivation these are the more common ones what is another realm and terms that are much more used these are much more zoology terms what's used far more often in clinical medicine is

a description of dichotomy between motivation and performance and that is never used more frequently than in the realm of making sense of sexual motivation in men as dissociable from erectile function versus dysfunction Motivation being very very different from performance so that's another realm of distinctions other Realms as well desire orgasms arousal all sorts of commonplace terms the performance versus motivation dichotomy and the proceptivity receptivity and Activity one are the major terms that are used next issue in terms of getting to this how do people find out information about sexual behavior one option is to sit

there with night viewing goggles and That's very useful for nocturnal species but how do people find out about human sexual behavior all sorts of ways over the years starting with Anonymous questionnaires but a really clever technique was worked out in the 1980s a biological mathematician named Joel con getting at how to get people to tell you about very embarrassing things about their sexual lives and this was prompted in the 80s when AIDS first swept in and it was wildly wildly uh Taboo at the time in virtually every corner of this country to admit to having

a less than standard whitebred sexual orientation take a look at the extended notes to see the trick that Joel con came up with a very clever device in order to figure out what percentage of people are doing what sexually without asking anybody to give an answer that they would find perhaps to be embarrassing or grounds for all sorts of persecution okay so beginning To look at aspects of behavior and other features of the sort of rightmost end of all of this we start off with the most Central puzzle in making sense of any of this

stuff which is so what's up with female orgasms and we've got right off the bat the simple problem of making sense of this biological phenomenon and one where fertility is not dependent on it one does not need to have organisms to become pregnant to give birth to pass on Copies of one's genes so what's the deal with orgasms first off a question we will wind up asking with a whole lot of the Behavior coming down the line is are we the only species and all sorts of careful Studies have shown that we are not the

only species other Apes other primate species as well monkeys and apes show orgasm among the females and that is uh detectable by all sorts of physiology we'll hear about in a while we are not the only species one of the Really bizarre pathetic things about trying to do research in this area was one of the first papers that ever demonstrated something which physiologically was identical to female orgasm in reesus Monkey females which wound up being a paper in this journal science down there in the footnotes the authors had to indicate this was not this did

not make use of any Federal grant money to carry the study just to give you a sense of where some of the Stuff sits okay so what's up with female orgasm it is not necessary for conception it is not necessary to increase the number of copies of your genes in future Generations despite that there is some evidence that it facilitates fertilization and the technical term that's always been given for that is bizarrely enough facilitation the notion is something about the vagal fluid something about the biochemistry of Increases sperm motility sperms swim faster and harder and

jump Upstream back to spawn or whatever it is the sperm are doing with more avidity with more energetic displays in an environment of more vaginal secretion and orgasm greatly increases that so the argument there being that orgasm facilitates fertilization through the sperm facilitation process evidence for that has always been a little bit indirect it is not airtight that that happens Another argument for why this increases fertility and this is sort of an interesting one and the notion here is that what an orgasm does is among other things exhausts you enormously causing you to be far

more likely to be horizontal than vertical shortly thereafter and thus facilitating fertilization because the sperm don't have to swim straight up Against Gravity I kid you not this is one of the leading models out there then there's the orgasm Facilitates female conception out of reinforcement Theory which is back to the it feels good and thus you are more likely to do it again and increasing the likelihood of passing and copies of your genes all of this is wonderful all of these possible mechanisms where even though female orgasm is not necessary for conception it nonetheless increases

the likelihood of that's great ever what most of the Studies have shown though is there is no relationship between the Fertility of a woman and her propensity towards orgasm it does not seem to play out in so far as any of this facilitation or horizontal swim enhancement techniques or whatever actually occurs these are not big enough of an effects to actually make a difference in terms of reproductive success so what else what else is known about it there is a certain degree of heritability of propensity towards orgasm in females and this is shown with All

our standard Behavior genetics techniques in terms of comparing dizygotic versus monozygotic twins we know what to do in terms of not overvaluing findings like those nonetheless they are there so if a basic puzzle is why do females have orgasms if it's not necessary for conception and in fact the evidence is not great that it even facilitates it why on top of all of that why such things as clitoral orgasms which the studies generally show are More easily brought about than our vaginal ones what's up with that even more of the same questions now somewhere in

there is lurking the heartbreaking possibility and making sense of why female orgasm exists the Dreadful possibility that what we're dealing with here is a spandrel that it is a spandrel it is simply baggage brought along that those guys have to go through this orgasm physiology to do any stuff with sperm And pass on copies of genes and all of that and it's simply baggage that the same physiology occurs in females that orgasm is simply a spandrel in women and the counter sort of scenario that's always given is this is exactly equivalent to the notion that

nipples are spandrels in men and that women female mammals need to go about all this lactation business and that's part of the whole package deal and you know just as it would be way too much work to Evolve females without orgasms it would be way too much to get rid of those useless nipples on men okay let's have a quick survey yes um could a lot of those questions also be applied to why why do males have orgasms ejaculation can OCC without orgasm okay so why do males have orgasms ejaculation can occur it is far

more voluminous in the face of an orgasm so that's easily framed in terms of uh an Adaptive mechanism okay quick survey here how many people okay how many guys Who have those useless nipples how many of you go for the nipple as spandrel and guys Theory whoa is that slow in the hands okay should I raise my hand should I not raise it okay uh women in the room how many go for the female orgasm is merely spandrel theory if I recall there was one other question somewhere a few weeks back that only got one

person fessing up to it and it came somewhere around there also so I Don't know if that's the lighting or if people tend to sit in the same places okay so not a whole lot of enthusiasm for the spandrel concepts here nonetheless that means needs to be seriously entertained okay so now looking at other features of the fixed action patterns and adid oh all these different species doing lordotic stuff and orgasms and ejaculation all of that what are some of the Realms of sexual behavior that are Relatively unique to humans first off one that used

to be thought to be absolutely unique was non-reproductive sex this is a world of difference than those species where the female ovulates for like two and a half hours every year and everybody mates at that point or species where somebody comes into heat a female is an estris humans have non-reproductive sex and that was viewed as absolutely unique what is now clear is it is not completely unique there are Lots of other species that do probably most famously bonobo chimps and various cations like dolphins nonetheless it is certainly a specialty among humans what else foreplay

that used to be in the category of human Specialties and it is clear by now that bonobo chimps for example have vastly more patients with foreplay than average humans do we are not the only species with that either huge huge controversy how unique is homosexuality to human behavior human Sexual behavior and what's clear increasingly is we're not the only species with that either the original view when people would view homosexual Behavior male male female female in other species it would be animals in captivity and it would be the wi why is there so much homosexuality

in prisons argument lack of Alternatives this was not normal natural behavior what is clear from ethological field studies is we are by no means the only species to Have homosexual Behavior what else one of the things that we do seem to be fairly unique about is having egalitarian sex which is to say that there are no human cultures where as part of the central sort of tenets of that culture people are restricted only a subset of individuals are allowed to reproduce and this is a world of difference from various species for example New World monkeys

marac sets where it is only one male and one female In a group that does the reproducing instead humans in every culture ever seen have egalitarian sex what else what else is highly human people used to think exclusively so this Endless Quest for variety and again just take a look at these the noo chimps and you'll see how small-minded we are when it comes to this but something else that is indeed unique to human sexual behavior is the notion that this is something you do in private there is no other species where The majority of

sexual behavior is conducted intentionally outside the sight of everybody else that is rather unique to humans what else about human sexual behavior seems to be specializations one that is fairly unique if not enti enely so is the subset of humans who psychopathologically confuse sexual behavior with violence and that seems not to have a whole lot of Precedence so immediately one asks other domains Masturbation that is not remotely a human specialty that is all sorts of other species as well and that used to get the well what else is there to do when you're sitting in

a zoo uh for the animals what else is there to do it is not natural it is a default whatever but looking at out in the real world and there is plenty of that and one of the most like implausible suggestions for an Adaptive just so story thing is why do male primates masturbate to the point of Ejaculation they tend to eat the semen afterward whoa great source of protein go the adaptationist everything has an Adaptive basis this one does not ring terribly true to me what else fantasy fantasy in humans is that unique to

humans obviously we hav a clue but here's one suggestion to me that this is not actually the case and this was years ago where I was watching my baboons and there was this one low ranking kid this snively adolescent kid with the nearest Thing he has ever gotten to a female in his life with some high ranking female in a bad mood beating on him and he's sitting there minding his own business and along comes I think by any baboon male standards the hottest female in the troop who has a peak estris swell is no

doubt ovulating that day comes walking along followed 2 feet behind by the huge menacing male who was in the concert ship with her an our guy just sits there and doesn't even quite look at what's Happening every now and then his eyes go up watching them go past and as she walks past he gets an erection and then goes off and masturbates okay the Charming I don't know if this is even the word you can use in this setting but the Charming notion is that we've just seen evidence for some sort of internal Fantasy Life

going on in this guy okay you could be a kill Joy instead and say no no she was giving off waffs of pheromones and that Was what was responsible for it nonetheless this is about as far as we can get at asking this critical question are we the only species that does this fantasizing stuff marriage clearly we've heard about monogamous parab bonding species in terms of the formal structure of marriage it is universal all human cultures have some version of it a across all human cultures more than 90% of people wind up in that culture's

equivalent of a permanent stable Relationship and this is the case in polygamous cultures we've already heard that business even though historically the majority of human cultures have been polygamous nonetheless amid them the vast majority of individuals have been in monogamous relationships amid that nonetheless what is also clear is amid that highly highly prevalent pattern of monogamy relationships there's a lot less monogamy going around than you would Think and this was first sorted out people like Alfred Kinsey when first working out that questionnaire approach to people's sexual behavior what became clear was there's a lot less

Faith within parab bonding within human spe within humans in this country andison shown in all sorts of other societies than one would originally assume there is social monogamy but not necessarily anywhere near as high of rates of sexual monogamy and what the paternity Studies have shown is in most Western European countries the rate at which children have been fathered by an individual other than the person claiming you know marriageable credit for doing so ranges between 10 and 40% of children how's that for a number okay what else what else tends to be a feature of

human sexual behavior what you have is of course not only intrinsic in the fact that there's a difference between social and sexual Monogamy you have cheating that is a human specialty in every culture what else is absolutely wildly human this notion of romance and romance is by most sort of estimates a relatively new invention in most cultures maybe a couple of centuries old and what is an even newer invention is the notion that romance passion Etc should persist should last throughout the entire higher duration of a lifetimes marriage that is an utterly novel concept that

is perhaps 30 40 50 years old in most westernized countries that's a new one as well what that of course ushers in is looking at issues of divorce across all cultures the average duration of marriages are 2 to four years and people have made the argument that that is the typical duration of children being dependent on a high degree of parenting of both parents being around that is the average interbirth interval 2 to four years in most traditional human cultures what's The term being described then if that is the natural point at which most marriages

dissolve and turn into other monogamous relationships the term that is given is that humans tends toward tend toward being serial monogamists moving from one monogamist relationship to another with on the average a lag time roughly corresponding to the inter birth interval so that's Charming what else what else do you have all sorts of other aspects of human sexual variety But ultimately when you look at human sexual behavior versus other species we are so boring we are so limited when you look at the range of unlikely things going on out there species that are regularly hermod

hermaphroditic and people in fact have done studies on how is it that a hermod animal does not try to have sex with itself and these are usually worm type things and that some version of an incest avoidance at the same time there are other species where Individuals change sex opportunistically all sorts of fish species where that happens lots of species that are parthenogenic where an individual reproduces without the benefit of anybody else's genetic input even stranger there's a bunch of snake species that are paragenetic but the females cannot reproduce paragenetically unless they mate with males

they do not actually get any sperm from the males and they get no genetic contribution but Something about that is necessary for the parthenogenic event to occur okay so all sorts of bizarri that make our fixed action patterns look really pretty dull but nonetheless these are the backbones of the human fixed action patterns and some of them wildly unique one some of them far less than people used to think some of them very very unprecedented okay so what this allows us to do now is make our first big step what's going on In the brain

what is the neurobiology of sexual behavior producing those fixed action patterns and what you better BET right off the bat is we are talking about the limic system this is all lyic system until we see ways in which it's not just all the lyic system but it is heavily centered no surprise in the limpic system and this was being noted first around the 1930s 1940s with the first experiment ments where there were lesion studies done damaging different Parts of the lyic system in animals and what would be noted was animals sexual behavior would change and

this was eventually termed a profile termed after The two scientists who pioneered this stuff called the clu buus syndrome which is when you damage some of these strange mysterious Rhino philonic sort of structures in there you change the sexual behavior you change for example in monkeys whether they are attempting to mate with another monkey as opposed To an animate object they change aspects of the fixed action patterns of the behavior and such and out of it this was one of the main driving forces on people saying nose brain well that's great but actually what we're

looking at is a part of the brain that has lots to do with emotion and emotionally related behaviors that was one of the driving forces on the lyic system being pulled together as a concept okay so what areas within the lyic system are relevant First pass there are different hotspots in there depending on gender among females probably the most important area is a subsection of the hypothalamus called the ventromedial hypothalamus involved in female sexual behavior what's the evidence for that just go back to last Friday's lecture lesion studies stimulation studies recording studies destroy the vmh

you do not get sexual beh Behavior anymore from a female stimulated and you will get the Same behaviors that you would normally only see in an ovulating female rat for example all the sorts of tools we heard about reinforcing this even more is this is the hot spot in the hypothalamus for receptors for estrogen and progesterone so that makes lots of sense meanwhile another region of the brain that is typically involved in sexual behavior in females a region the midbrain the midbrain which seems to have something to do with some of the hormonal aspects Of

sexual behavior that are specific to females finally back to that lordosis reflex you got to have a spinal cord to full pull off the full array of typical mamalian female sexual behavior so spinal Pathways which do not exist in males lordotic reflexes the back arching reflex is exclusively a female one meanwhile over on the other side of things there are regions in the brain that tend to be more specialized for sexual behavior in males than in females A different part of the hypothalamus called the medial preoptic area and the exact same sort of evidence is

for the ventral medial hypothalamus in females lesion studies stimulation recording studies all that sort of thing and you guessed it whopping great amounts of testosterone receptors Androgen receptors within the medial preoptic area very interestingly something we will hear more about next week or so is another region of the brain is involved In male sexual behavior which is the amydala HM that's kind of interesting the amydala we've already heard about amydala fear anxiety all of that but the amydala also plays a very major role in aggression and there's a little bit a small domain of amygdaloid

fun in males that's involved in sexual behavior involved in sexual motivation medial preoptic area is much more about sexual performance in males amydala is much More about SE sexual motivation and all sorts of people have speculated fairly reasonably I think that this may have something to do with the fact explaining why among humans it is far more likely to be males than females who go about confusing sexuality with aggression that it's got something to do with this weird role of the amydala in male sexual motivation male sexual arousal what else okay males have penises thus

they're the only ones who Can have penile erections and to do that autonomic nervous system and what we will hear about what you already heard about in the introduction to the autonomic nervous system but also in the zebras book is that whole business in order to manage that to pull that off initially it is parasympathetic nervous system that is establishes the erection the process of arousal involves the transition to sympathetic full blast sympathetic nervous system needed for Ejaculation that's what all of that is about exclusive to males but then it turns out it's not exclusive

to males because it's virtually the exact same physiology underlying clitoral erections in females the same exact sort of thing which of course brings up the dangerous possibility of another spandrel in our laps here in terms of making sense of that I didn't say that just now did I say spandrels in your lap okay bringing up that possibility that is not specific To male physiology what is specific of course is stuff that's going on with penises in terms of blood flow there's generally a dichotomy between species between whether or not males get vascular erections or muscular

erections vascular erections you increase blood flow into the penis and you stop it from going out the other end and thus you get vascular driven engorgement as DH Lawrence would no doubt have described it alternatively in lots of species There are muscular erections there is a muscle for example found in rodent penises called the erector Levy muscle well that's not too surprising that it's called that and a whole bunch of cell body neurons in the spinal cord responsible for pulling up the sail or whatever it is you do there and what you get are differences

in general the muscular driven erections occur a lot faster the vascular ones the hemodynamic ones last a lot longer take your pick But it's essentially the exact same autonomic physiology in both cases finally one other thing factoid a useful one we heard last week which is in so far as there's very similar physiology to orgasms in both sexes there's that difference in recovery time how long it takes for the sympathetic nervous system to go back to Baseline postorgasm and on the average a substantial sex difference in that yes everybody managed to guess it last week

Which direction it went a far slower recovery time in females than in males in terms of underlying neurobiology something that was a major finding in the field were brain regions that differed in size depending on your gender in including in humans and this ushered in a whole world of sexual dimorphism in the brain and there have now been shown to be all sorts of brain regions where on the average you get differences in the size of nuclei you Get differences in the number of axons going through a bundle a fiber all of that and we

will hear about some more of those down the line but the one that has gotten the most attention in terms of sexual behavior is a cluster of tiny nuclei in the hypothalamus called the in cluster the internuclear interstitial nucleus of the anterior hypothalamus do not write down what that stands for but it's a little nucleus in there a little subset of neuronal cell bodies where you Get a very substantial sex difference in the size of this area where on the average it is about twice the size in men as in women and back to the

other weeks sort of rant about statistical significance versus magnitude this is a big effect it is almost almost in the range where you can identify the sex of somebody by looking at the size of this nucleus in their brain postmortem in rodents you pretty much can a very reliable two-fold difference males Larger than females as we'll hear in a while one really interesting exception to that okay so either some areas of the brain that are preferentially involved and activated by sexual behavior depending on your gender or regions that differ in size substantially by your gender

but then at the end of the day there's all sorts of things that are absolutely in common again the physiology of orgasm exactly the same what clinically the picture is is males Having problems with the whole system the problem tends to be too rapid of a transition from parasympathetic to sympathetic in other words the world of premature ejaculation the more typical medical problem in women is failure of the transition from parasympathetic to sympathetic inability to reach orgasm and it is of course a huge sociocultural political philosophical argument whether that counts as a pathology or normal

human variability I'm not going anywhere near that one but nonetheless that is the more common pattern neurobiology that's absolutely Ely in common between the Sexes which is all of that stuff at the very beginning of why are they in such a rush at the end the neurobiology of pleasure and the neurobiology of reward and of anticipation and this is this whole world of as we know already dopamine the role of dopamine in sexual behavior is virtually identical in both sexes which Is to say it plays a huge role you find circumstances where you deplete dopamine

from the relevant brain regions back to last Friday lyic system you remember that ventral tegmental area which sends that big dopaminergic projection to the nucleus accumbent which then passes it on to all sorts of places in the brain deplete that pathway of dopamine and you're not going to get a whole lot of interest in sexual behavior you are not going to get a whole lot of libido Proceptivity what's the class classic circumstance where you see depletion of dopamine there and loss of proceptive libido clinical depression that's one of the defining symptoms of depression amid the

various numerous forms of pleasure that go down the tubes loss of sexual interest one of the defining symptoms so the dopamine system the general term given for this is the mesolimbic dopamine system to distinguish it from some of the other Ways the dopamine is used in the brain the mesolimbic dopamine system is absolutely Central to the reinforcing aspects of sexual behavior so what's the evidence for that first off back to that distinction that I think I brought up last week I wasn't paying attention but I think I talked about which is the dopamine system there

is not so much about reward it's about the anticipation of reward did I talk about that in monkeys pressing levers yes okay I Should probably read the extended notes at some point look at the film of this okay what you see there is the dopamine is about the anticipation of and the dopamine as we heard is about also fueling the behaviors needed to achieve the reward dopamine in this mesolimbic pathway as driving goal directed behavior and that is certainly the case with sexual behavior by now there is a whole literature involving humans where You stick

them in brain scanners and you do something or other sexually arousing or interesting or something or other to them and then you see what parts of the brain activate and it's these dopamine Pathways consistently way up there showing just how subtle this can be how's this you take men there's been a whole literature by now showing that you present people in brain scanners with pornography and that must have been a really interesting human subject's Release for you worked out but showing in both sexes what you tend to see is activation of dopaminergic regions we will

hear in a little while a sex difference in that domain that will probably not surprise anyone but how's this for subtle you take a guy and you show him the picture of someone of the opposite sex if he is heterosexual and you show him the picture of this individual and if it is someone who he assesses as being attractive you don't Necessarily get this dopaminergic path way to activate it depends what this study showed was if the person is making what would pass for eye contact if they are looking straight out the dopamine system activates

and if they're looking elsewhere it doesn't activate how's that for classic male sort of responsiveness if it looks as if this attractive person is looking at you it activates even more distressingly from this study when you show men on the average blah blah Pictures of women who they would rate as being unattractive it's when they're looking away that the dopamine system activates oh my God what is going on here this is pitiful what also has been shown is the exact same eye contact phenomenon of gay men looking at pictures of attractive men another theme we're

going to see over and over which is sexual orientation being pretty much trivial in terms of how it influences some of this Neurobiology just switch the gender of the other individual and it works exactly the same now when you look at this business about dopamine rising in anticipation of a reward rather than in response to the reward itself it brings up one of the doesn't bring that up it brings up one of the all-time interesting studies that was published about a decade ago okay so the Paradigm I described last week you put on the light

which tells the monkey that okay We're starting one of those sessions where if you press the levers adequately you will get a reward and they now carry out this behavior and as a result they get the reward here and as we saw dopamine doesn't go up after the reward it goes up at this point this is the I know how to do this this is going to be great this is terrific here's where you get the rise and dopamine this is not only the anticipation but if you don't have this rise you don't get the

Behavior the goal directed Behavior now in This brilliant study what they did was transition from a paradigm where okay the monkey presses the lever 10 times and gets the reward now what you do is the monkey works and it gets the reward only half the time it gets only a 50% reward rate reward rate unpredictably and what happens to dopamine okay got your choice what's your vote it doesn't rise as much it rises the exact same amount It rises even higher okay you guys all understand anticipation and gold it does this it's one of the

biggest Rises you will find dopamine in the brain short of cocaine what have you just introduced into there this is I'm all over it I know how this works this is going to be great I have Mastery and control I am the captain of my own lever pressing this is all about that what's this about this is what dopamine does when you have introduced The word maybe into the equation and that is incredibly reinforcing and people will work like mad in contexts of maybe far more so than they work in contexts of certainty psychologists have

known this forever this is intermittent reinforcement you never get more Behavior out of an organism than when you have introduced a maybe into it and part of the Brilliance of the study was what they then did now animals either Got reward 25% of the time or 75% of the time on a certain level these are diametrically opposite manipulations in one you're getting more rewards and the other you're getting less what's the thing they have in common they both had smaller Mayes than the 50% version and what you see is it would look like this 100%

25 or 75 50% maximize the maybe and one of the most brilliant things that various social Engineers do with humans is convince people that there's a 50% Maybe when it is not 50% in the slightest that's what Las Vegas is about that's an entire world of very smart psychologists making people think in circumstances where there's like one tenth of 1% of a maybe going on there that is actually a 50% and when you do that you get dopamine like crazy and you get go directed Behavior as a result really really powerful and this is so

strongly the case that this explains an extremely cynical uh thing that a guy I Knew in my dorm back when used to say all the time how's this for like a dispirited view of what life is like but possibly absolutely accurate which is a relationship is the price you pay for the anticipation of it how's that for a grim world viiew go figure this guy had what a string of disastrous relationships but what you see here is introduce a maybe and it is very very powerful one final piece of the dopamine system here that is

pertinent which is As you might expect from all of our molecular biology stuff there's all sorts of different dopamine receptor subtypes and two of them are pertinent to this world of sexual behavior and reward what is called the shockingly the D1 dopamine receptor and the D2 dopamine receptor and what studies show is in monogamous species what happens is right after mating when a pair bond is first formed the second that's over with levels of the D2 receptor go way down You down regulate the levels of the receptor and you upregulate the levels of the D1

receptor what's that about if you drive down the D2 levels before they even mate they don't form a parabond if you prevent the decline in the d2s after they've made it and parab bonded or if you prevent the rise in the d1s they'll parir Bond and then 8 and a half minutes later they'll go and pair bond with somebody else the d2s seem to mediate the rewarding anticipatory Aspects of pair bonding the d1s on a certain renti level seem to mediate the pleasure of the monogamist the truly monogamous features of the parabon so very interesting

interaction between the two okay one last thing now about dopamine and this one is like even more depressing than relationships or the price you pay this was a study which was really like someday may come to haunt you majorly and in this study what they did it was another one of those brain Imaging study ones and what they did was they took people in two categories in both cases these are people who had found their beloved their beloved the person who was their soulmate the person in whose arms they were going to die someday the

person and they divided between these two groups one was a group where they had known the person in whose arms they're going to die for like two and a half weeks and the other is when they had been together for more than Five years so you pick you put somebody in the brain scanner and you start flashing up at speed subliminal speeds of pictures of individuals they know important control in the study and embedded in there is a picture of their beloved and suddenly somewhere along the way up flashes the picture of their beloved be

in a short-term relationship and the dopamine system goes crazy and activates like mad now you come back Five years later into that same relationship with the Beloved and you do the exact same thing and you flash up their picture and the dopamine system doesn't activate what activates instead was that anterior singulate thing we heard about on Friday having to do with empathy and comfort and all of that in other words what we see here is the neurochemical transition from one's beloved from causing like your blood to run scalding hot to your beloved being Like a

comfortable old armchair this is one depressing study so let's take a f minute break to contemplate that one okay and then we will resume lots of good questions just now during the break uh disappointingly few along the lines of I've got a friend who so not a bunch of those but let's see a number of questions first one can I repeat what I said about the D1 and the D2 receptors okay these are different types of receptors for dopamine in other Words they all respond to the same neurotransmitter dopamine but in different ways and these

receptors are found on different neuron types you're getting into all sorts of different Pathways what you see is in rodents in pair bonding rodents they better have elevated levels they better have D2 receptors on neurons being fed by this mesolimbic reward dopamine pathway they have to have D2 receptors to form the parabond for the attachment to Occur the second that happens you need to have low levels of D2 and high level levels of D1 to remain faithful in your parir bonded relationship so what you see in these vs is right after the parir bond occurs

there's down regulation of the d2s and up regulation of the d1s and if you prevent that from happening the pair bond that's been formed does not prove lasting so that's what I was saying there somebody brought up the great Question which I was going to say something about and forgot which is well how about like D2 D1 ratios in humans and their sexual behavior stuff and there's been one study showing that a higher ratio of D2 to D1 predicts more stable relationships small effect not replicated yet but nonetheless that's kind of interesting so on a

certain level then D2 seems to be required at least shown in rodents who knows about us D2 is about the formation of the Attachment D1 is about the maintenance of it the faithfulness of it if you will next somebody bringing up the issue in terms of female orgasm maybe what female orgasm is about is a mate selection mechanism as in individuals who uh increase your likelihood of having orgasms or ones you are more likely to lower your D2 receptors for but the one problem with that one that makes wonderful sense what the studies tend to

show though is Likelihood of orgasm is much more a function of who the female is than who the male is that they are with arguing against that let's see finally no not that okay so we already covered that and there was one additional question okay so what's the driving force in terms of the proximal reinforcing pleasurable aspects of sexual behavior what's up with why only some species us predominantly have non-reproductive sex you can have sex all the time versus Other species that only do for reproduction what that means is in other species the Endocrinology of

ovulation is the thing that makes sex pleasurable and we will see shortly what that's about in females it's the hormones associated with ovulation that sensitize various tactile receptors to respond in ways that mediate proximal pleasure and in males it's the female giving off for example the right pheromones the right releasing stimuli driven by the right Hormone levels that constitute the proximal signal of pleasurable anticipation and what you find in humans is it doesn't work that way you do not need for example in women the elevated levels of estrogen typical of ovulation in order to have

tactile responsiveness to sexually arousing stimuli stay tuned though it's easier though when estrogen levels are higher okay final brain region relevant to all of this this is the frontal cortex we already got a First pass at the frontal cortex last week and frontal cortex regulating your behavior impulse control all that sort of thing gratification postponing this plays a large role in sexual behavior what's the easy immediate explanation that one can come up with what the frontal cortex does is it makes you be appropriate in your sexual behavior it teaches you the appropriate context it teaches

you what aspects of proceptive sexual behavior is not a good idea it Keeps you from doing things you would regret vastly afterward that's a very easy version of it and commensurate with that you see lots of circumstances of individuals with frontal cortical damage doing highly inappropriate sexual behavior one example of it one of those horrifying things that can happen this was a case that actually happened in a nursing home in inas in the East Bay a number of years ago this was a man in his 80s who had had stroke damage to his Frontal cortex

who was found to have raped a woman there another 80-year-old with Alzheimer's disease damaged the frontal cortex and all sorts of the this is not sexual behavior that you do constraints go down the tubes just as importantly though what the frontal cortex with all of it's giving you the discipline to do the right thing some of the time with that Tak takes the form of is getting you to do proceptive sexual behavior for example you are trying to Do some courtship of some other antler ulet that you are courting and this is terrifying because there's

another individual challenging you and it is the frontal cortex that is getting you to carry out those sexual behaviors at that point even if it is a terrifying circumstance nonetheless what the frontal cortex mostly is about is reigning in sexual behavior Fe it's not changing the fixed action patterns of sex it's changing the context in which The fixed action patterns occur so now we are ready to look at one more feature of the neurobiology which is when somebody is having sex what hormonal responses are triggered notice this is not here this is not what hormones

have to do with bringing about sexual behavior this is what are the hormonal responses to sexual behavior starting off in females including human human females having sex increases secretion of progesterone derived Hormones and that has something to do with reinforcing the pleasure interestingly in females the world over having sex increases the level of testosterone related hormones in the bloodstream androgens women females generate androgens Maybe 5% the levels you see in males and they come out of the adrenal glands and they play they seem to play a very Central role in mediating sexual motivation sexual arousal

in females how is that shown Obvious experimental studies with Lab Rats how is that shown in humans when women have any of a number of types of diseases where you have to take out the adrenal glands sexual motivation sexual arousal goes down give them placement androgens and sexual arousal sexual proceptivity returns so Androgen they playing a role probably most importantly in terms of hormones triggered by sexual behavior in females is the release of Oxytocin oxytocin is really interesting we've heard about oxytocin twice already one is when it's coming out of the posterior pituitary and the

second is that minor business the other day last Wednesday of oxytocin being another one of those hypothalamic hormones that helps to release act from the pituitary remember it doesn't directly release it's a modulator of CR action if then claw Etc but those are the two ways we've heard about oxytocin oxytocin also Works in the brain as a neurotransmitter and neuromodulator and what does it do there it appears to play a very Central role in forming attachments a very Central role in forming of parir bonds and it along with dopamine and the D2 receptors are critical

for female vs of monogamous species to form parir bonds female humans when having sex secrete lots of oxytocin and activate oxytocin Pathways in the brain and it appears to play a Role in the formation of attachment interestingly how is this a whole body of research now showing that if you introduce oxytocin into the brains of humans experimentally they become more trusting amazing body of research where you take aerosolized oxytocin and you Spritz it up people's noses and what they showed in the studies were number one one type of study you then Play a clip of

somebody making an argument for Some stance and some debate and people believe the person more they find their argument more convincing they trust the person more or the other version that's been shown is you Spritz oxytocin up the noses of people and you make them more Cooperative in their game theory play the ways at which they go about playing prisoners dilemma and other games we will hear about later on as well this has given rise to A Whole New Field I kid you not called Neuromarketing the notion that if only you could Spritz oxytocin up

the noses of people right before your television ad comes on they're going to believe you when you say it will make you happy to buy our thing and they will fall for it there are actually neuroendocrinologists making a living now selling their wees to neuromarketing people you know self proclaimed ones no doubt they are spritzing oxytocin up the noses of those you know capitalists to Get them to hire them to do this but oxytocin playing a role in this so that's kind of interesting because what's oxytocin mostly doing in the body the vast majority of

oxytocin is not the stuff up in the brain in these Pathways some of them impinging on dopamine releasing neurons the vast majority is not the oxytocin sitting there in the hypothal is doing something or other to act in the pituitary the vast majority is the stuff coming out of the posterior Pituitary and what does oxytocin have to do there it has to do with milk let down it has to do with nursing and suddenly instead it's playing a role in forming sexual parab bonding and the argument is made that attachment monogamous attachment sexual attachment is

in some way evolutionarily a descendant of the neurobiology of mother Offspring attachment that that's where it is originally being driven by so oxytocin playing a role there as well meanwhile Over at the male and of things upgo testosterone levels during sex in a surprisingly linear way the more sexual behavior in a male the higher testosterone levels are found afterward critically critically stay tuned for a little while these are elevations of testosterone in response to sexual behavior as we'll see the evidence that high testosterone levels make males more sexually active is basically non-existent so critical critical

Proviso here this is sex increasing testosterone secretion not the other way around what else meanwhile back to the posterior pituitary was that a question nope okay that was a head scratch okay back to the posterior pituitary the other hormone coming out from their vasopressin and oxytocin is to females as vasopress is to males and we've already heard something about this back in the molecular genetic stud and those if then Clauses and unlikely ways in Which you get mutations vasopressin vasopressin also is found in the nervous system where it serves a neuromodulatory role and vasopressin is

critical for forming a parir bond back to that business about when you look at monogamous versus polygamous species what's going on what you have uniquely in the monogamous species is Express of the vasopressin receptor gene on neurons that release dopamine another words males secrete Vasopressin and if you are of a species where vasopressin now goes and stimulates dopamine neurons you decide you really really really liked having sex with this other V and you come back for more and that's the driving force on the formation of the parabond incredible studies showing that if you take male

vs from the polygamous species and do to Gene transfer techniques I've mentioned the study already but you now stick vasopressin receptors into those Dopamine neurons those polygamous males now become parir bonding males they now become monogamous so really interesting what you then see in these studies is you look at these monogamous species where the males have vasopress receptors on these dopamine neurons and you look at individual males and the ones who have more receptors there are forming parir bonds faster it takes fewer rounds of mating with a female to form a Parabond so what about

primates so you start off looking at two different primate species one parab bonding maret Monkeys new world Marmet monkeys and then one classic tornament species polygamous primate spe species Rees monkeys and what you see is you've got the variant the monogamous V vasopressin receptor Gene variant in the parir bonding monkey species in the marbet and you get the polygamous version of the gene in the uh Reese's Monkeys so it maps on there as well so the more of this receptor in these dopamine Pathways within monogamous species the more rapidly they form form a parab bond

and what you see is differences in the mere presence of them in comparing parab bonding versus non-p parab bonding rodents and monkeys so how about humans first thing that comes up is among the Apes you also find the two variants the monogamous V variant of the Dop of the vas pressent receptor Gene and the polygamous male variant so what species do you see it in in chimpanzees you see the polygamus bow species version that makes lots of sense they are a major polygamous species in their behavior but then this beautiful dichotomy comes crashing down when

you see that you've got the monogamous Gene version in bonobos and as we will hear about in a while bonobos are the most hyper Polygamous Le hyper variety of sexually behaving organisms on the entire planet they are as far as you could get from a monogamous species as you can ever ask for if you ask for such things and you got the wrong type of vasopress receptor Gene whatever is going on it's more complicated than the have the version that winds up on the dopamine neurons and you are going to have 50th wedding anniversaries if

you are a v or you are a maret and it's got to be more Complicated than that so how about humans and what you see is not explicitly as much genetic variability as some people having the monogamous Vol version and some people have the polygamous but nonetheless you get variation the gene basically is about halfway in between whoa we keep having that theme over and over all these different ways of looking at body size and sexual dimorphism and imprinted genes and all that stuff and humans keep Winding up being about a halfway between a classic

monogamous parabond and a classic polygamous tornament species so the basic human version of it is somewhere in between but you get variations you got genetic variations that either look a little bit more like the monogamous V version or the polygamous V version and what studies have now shown two different studies independently showing this have the monogamous V version and with a small Effect you are more likely to get married you are more likely to remain married and both you and your partner are more likely to rate the marriage as stable and happy that's kind of

interesting finally in terms of the role of vasopressin in terms of attachment and males all of that and in terms of social connectiveness a large body of studies now have shown mutations in the vas oppress receptor Gene okay anybody Want to get what guess what disorder you find it have people I put that in the extended notes haven't I people have read it already I know I fell for it last time I am not falling for that stupid trick again of asking you to prove he sniffed some oxytocin so does anybody want to guess swich

the okay what you now all know is there's now been a lot of demonstrations of mutations in the vasopress receptor Gene in family pedigrees with autism a Disease of very very little attachment to other humans so we've got written all over the place here is some sort of role of oxytocin in female attachment formation and vasopressin and we've already gotten interesting hints that this applies to humans and we've already gotten interesting hints that individual differences in the molecular biology of these genes predicts something about individual differences and the stability of relationships in Humans okay so

everything we've been hearing about with the neurobiology and we're still living in this part in this bucket here temporarily has been built around heterosexual relationships what's known about the neurobiology of sexual orientation what has been found is most strikingly one Landmark study one that got on the cover of Time Magazine one that had a gigantic gigantic impact which was looking back at that hypothalamic nucleus that inah in ah yes Where what we saw before it was very reliably on the average men their size of it is about twice the size as in women and in

other species males about twice the size as in females and a study was done in the late 80s by a neuroanatomist named Simon L LA is one of the all-time great neuroanatomist he was trained by huil and visel was a professor at Harvard Med school for a while before moving to the sock Institute and what he did was look Postmortem at the brains of a bunch of individuals where he knew the sexual orientation men and what he showed was gay men on the average had this nucleus on the average was half the size that you

saw in heterosexual men on the average it was about the same size as you saw in heterosexual women amazing Landmark study everybody learned about the homosexual brain from the study hugely widely reported and this is kind of interesting okay what's interesting About it first off the question you need to ask is how much variability fair amount it wasn't all that reliable of the difference on the average it was about a half the size next thing you would want to know is has anybody replicated it since then yes next thing you would want to know is

where did L get the brains from and these were predominantly from gay men who had died of AIDS is that a confound is that going to perhaps atrophy this Part of the brain nobody knows so that remains as a caveat in that study what was striking though was everybody learned about this finding this became famous L became extremely famous for this and what was also very interesting about it was the political context of this finding a few years before that another group had reported another difference in the hypothalamus based on sexual orientation and this [Music]

Was there it is and what you found was in this part of the brain on the average it would tend to be bigger in women than in men and what these guys reported was in gay men it tended to be big bigger than in straight men what was puzzling about this study was this was a part of the hypothalamus having to do with regulation of like your kidneys and it was totally ignored and completely bizarre except there was one thing that was done with it which Was this was viewed as a totally offensive study in

the gay community this was viewed as an attempt by scientist to pathologize sexual orientation to say you see we found something wrong in the brains of homosexual men this part of the brain is bigger than it should be it's bigger than it's supposed to be there's probably two reasons why that occurred the first one was that scientists who did it were straight and the second Reason being that they were a Dutch group and I am willing to bet unconsciously there was something central European Nazi Echoes of Germanic sounding authors producing this finding which there is

no shortage of history in the gay community for being skittish about Nazi Notions of what normality is in human behavior and human brains this finding got widely condemned in the gay community out came L with his finding and he became the most beloved Neuroanatomist ever in the history of gay communities one probably important feature reason for it is that L was gay very openly so another reason was the part of the brain he found made sense it had something to do with sexual behavior as opposed to this totally puzzling thing so what was this about

very interestingly the explanation almost certainly is that this was the part of the hypothalamus next door to the area that L studied and if this part was Smaller in gay men simply because of just physical constraint stuff this part could get bigger in gay men because this one was taking up less area that's probably what was going on what's really fascinating though is the political context that this research was done in and this was that first group the senior author of it a man named dick Schwab and he got death threats because of that study

reporting ooh here is easily interpreted as something wrong in the Brains of gay men and Simon L became the hero in the community this was utterly embraced by the community because in large part how it was interpreted as this is biology this isn't choice this is biology look at this this is ridiculous as saying oh my God if we have gay teachers in the classroom we will turn the Boy Scouts of America into gay men oh my God if we have blue-eyed teachers in the classroom the usual argument that this is absolute gibberish To demonize

sexual orientation as a choice look at this there's a neurobiology of it and this was embraced sufficiently that I've have seen people in the Castro District in San Francisco this is disappeared somewhat showing the half-life of neuroanatomical knowledge but during that time people in the Castro District up in the city there which is a very gay community I have seen people with t-shirts saying the other term people never really wanted to Embrace this inah so its nickname was the sexually dimorphic nucleus of the hypothalamus and I've seen people with t-shirts saying the only small thing

about me is my sexually dimorphic nucleus they were actually selling T-shirts that would say this during gay pride parades around 1990 or so isn't it great when people learn neuroanatomy out in the general public there okay so an interesting brain difference confounded by people who died of AIDS it's still Not clear what that means in terms of possibly negating the finding at least independently rep licated fascinating piece of not science but the political context of of science this Politically Incorrect to an extreme this very very widely embraced one interesting thing is that paper by L

was published in the journal science again constantly mentioned as probably the most influential science journal in this country and it was published what year Was it 88 8892 90 okay I'm getting the year wrong but it was just before the Clinton Clinton election against Bush where one of the big issues was gays in the military that was the first thing that Clinton turned to after he was elected I happened to know the man who was the editor of science at the time and they timed the publication that paper came out in late October that year

and they held it for that time because they knew That this was going to be an issue in the election which was kind of cool that they did that although some people may disagree okay but we hurdle on so what other biological neurobiological differences as a function of sexual orientation another one that comes through over and over and over again which what do you make of this is apparently there is a reliable gender difference in the length of the second finger versus the fourth finger the Ratio of the two and just to show how B

whoa did a lot of hands just go up in this Auditorium and just to show how biologically compelling the explanation is for it I don't actually remember which like who's got the greater 4 to2 ratio which sex or whatever but it is a very now people are checking each other's hands okay the first wave and now all this chimp hand inspection stuff happening in here and what has been shown quite reliably since then is on The average gay men tend to have the finger length ratio of straight women rather than of straight men a small

effect there another even more bizarre finding which is there is something called the auto acoustic reflex and what that is is if you sit there and plug your ears up with your fingers you will hear a noise that's just coming from the intrinsic vibration of something rather in your ears and that's the auto acoustic reflex Generating some low Herz sound in there and the rate of the oscillation differs by sex in humans which no doubt explains everything about the tragic Wars of the Sexes and why people just don't understand each other by gender because of

their ears vibrating at different speeds but what these Studies have also shown was gay men having the auto acoustic reflexive vibratory speed more typical of straight women and straight men again a very small effect What are all of these about the assumptions are it's got to do with something with prenatal hormone environment stay tuned we will be coming back to this now some somewhere in there you may ask okay well what about the neurobiology of sexual orientation in women vastly smaller literature far far less studied what has been showed so far are only two endpoints

one is the same deal with the fourth to Second finger ratio on the average gay women have the Ratio more typical of straight men than straight women the other thing that's been shown is the same Auto acoustic reflex thingy going on there final realm of neurobiology rather than issues of gay versus straight what is the neurobiology of transsexuality and that used to be considered to be purely a domain of Psychopathology if being gay used to be a certifiable psychiatric disorder up until the early 1970s the American Psychiatric association in their textbook the diagnostic statistical manual

you could be psychiatrically certified as ill a psychiatric disorder was being [ __ ] ual or lesbian and then in what had to have been one of the more all-time blowout committee meetings ever they decided that no actually it's not a psychiatric disorder and overnight about 40 million Americans were cured of a psychiatric disease the notion of transsexuality as a psychiatric disorder Has had much much longer shelf life what's the neurobiology of that to date there have been a handful of studies and they show essentially the same thing really really interesting another region of the

brain that shows a sex difference in its average size don't even worry about the name of this it's called the bed nucleus of the stria terminalis it's where the amydala begins to send its projection into the hypothalamus another one to those gender differences there's One type of neuron in there with a certain type of neurotransmitter where very very reliably it is about twice the size in males than in females sufficiently so that even in human brains you could pretty confidently determine the sex of somebody by seeing the number of these neurons you'll see I'm not

even saying the name of the neurotransmitter it's irrelevant it's just another one of those differences a dimorphism in a region of the brain a Really really reliable one and this was a study done by some superb neuroanatomists looking at transsexuals and what they showed was very interesting which was very very reliably and a very powerful effect what you would see in their large large sample size of transsexuals brains postmortem was people would have this part of the brain the size not of their sex that they were born with but rather of the sex they insisted

they always Actually were wow immediate questions one must ask okay well maybe this is due to the fact that when people change gen gender transsexual procedures there's a whole lot of hormones involved and maybe that's doing something to this part of the brain critical control that they had was this was looking both at transsexuals who had made gender changes and those who went to their deathbed saying this is not the sex that I am I Got the wrong body but never made the change it wasn't a function of having actually gone through the transition and

the endocrine manipulations with it another control they had which was looking at men who would get a certain type of testicular cancer where they would have to be treated with certain feminizing hormones in other words very similar to some of the endocr treatments of male to female transgendered individuals and postmortem you didn't See the changes there it has nothing to do with the hormones it had to do with the person insisting from day one that they got the wrong body and this was a landmark study fabulously well done and controlled and replicated once since then

showing that what transsexualism used to be thought of is that people who think that they're a different gender than they actually are what this study suggests is what transsexual is about is people who got the wrong gendered body And these are people who are chromosomally of one sex in terms of their gonads they're of that sex in terms of their hormones they're of that sex in terms of their genitalia and their secondary sexual characteristics they are of that sex but they are insisting that's not who I really am this part of the brain agrees with

them also very interestingly that study was done by the same Dutch scientists who did this one again this is very Complex Terrain in terms of what these things wind up implicating interestingly that study was published right around the time that the city of San Francisco did something very cool which was for city employees now medical insurance will cover transgender operations however there's no evidence that the Obscure endocrine Journal published at a lvia or something did that like the afternoon before you know the San Francisco Commissioners had their Meeting on that one but nonetheless this is

a subject with all sorts of Realms of implications one additional study about transsexualism okay how many of you know about Phantom limb syndrome okay you are are a guy with a penis and you get a certain type of penile cancer and what's often done is your penises exis that is cut off and about 60% of men who have had to have their penises removed because of cancer there wind up getting Fant of P Phantom Penile Sensations which I don't want to know about what you see though is when you take transgendered individuals who go from

male to female in other as part of it having their penises removed 0% rate of penile Phantom sensation suggestion being that there is something much more normal in that case than when a penis is being removed for cancer a whole new area of research very novel very challenging okay so this has given us a Sense now of this bucket and we are now ready to move on to what in the environment releases some of these fixed action patterns of sexual behavior what in the environment is doing this or that to the medial preoptic area or

the amydala or vasopressin receptor levels or any such thing what are the sensory triggers for the neurobiology of sexual behavior okay right off what is obvious is we are in ethology Ville here it's going to depend on the species which Sensory modality is most important and this is once again the crushing of the limpic system equals nose brain concept lyic system equals nose brain if you are a rat it's once again going to be interviewing an animal in its own language you've got species where the releasing stimuli are all Visual and we've heard one example

of that already which were the pathetic male turkeys getting faked out by the styrofoam female turkeys with the feathers Pointing the wrong way visual stimuli other species are quite visual as well primates non-human primates it's monkeys for example and what Studies have shown is how's this remarkable okay here we have um nah forget it okay you will take a rees's monkey a rees's monkey from a social group and he is sitting there and he can lever press for various rewards and he will press a lever a certain number of times to uh get some juice

as A reward he will press a lever a certain number of times to see a high-ranking male from his social group no doubt to keep an eye on the guy he will not lever press to see a male who is lower ranking than him but he will lever press the most to see pictures of female rees's monkeys who are in heat whoa is that weird or what and the bigger the estris swelling on the female the more lever pressing the male will do to be able to see This so that's kind of interesting in this

close relative ours in terms of visual stimuli what is also known is humans are highly visual in their sexual responsiveness as well visual stimuli as releasing stimuli what is no surprise whatsoever is on the average males are more responsive to visual releasing stimuli than are females among humans and this has been shown in various ways for example now studies using brain Imaging showing that for visually Sexually arousing material that not only are men on the average subjectively more responsive but you get more of an activation of dopamine dopamine Pathways in men than in women what's

interesting also is that in men you uniquely get activation of that area of the amydala as well and again that weird world of the structure of the brain heavily involved in aggression also being involved something about male sexual motivation what else then there of Course is the world of tactile stimulation and what you've got is a whole domain where not surprisingly stimulate the ra the right tactile receptors and it is sexually arousing are they sure have they done enough research on this and you will activate dopamine regions all of that making perfect sense what also

makes perfect sense is some types of tactile receptors in some part of the body activate dopamine more than other types and we Are now in the whole world of erogenous zones and that whole deal what is also clear is that these receptors these tactile receptors their responsiveness to stimuli will change depending on your hormone levels and what you see is in women tactile responsiveness the extent to which tactile stimulation of skin throughout the body but especially of genitals tactile stimulation evokes more dopamine activation when somebody is ovulating in other words birds at Ovulation women's skin

is more sensitive to sexually arousing touch in men it requires testosterone men who are castrated tactile responsiveness to stimuli goes down in terms of finding them pleasurable sexually arousing final domain of tactile stuff the specialized version we've heard of already that lordosis reflex business again that's a spinal reflex but this is not a spinal reflex bopping somebody on the knee and their leg goes flying out this is spinal Reflex where you only get the lordotic arch backing and females Arch backing back arching okay you don't get either but you especially don't get the arch backing

when you don't have elevated estrogen levels only when females are ovulating are those tactile receptors sensitive to pressure on the flanks of the rear end and out comes the reflex there so tactile stimulation at the end of the day though without question as agreed upon by every scientist on Earth The coolest sensory modality for sexual releasing stimuli are olfactory cues pheromones and thus we enter the Magnificent wonderful world of pheromonal communication and pheromonal sexual arousal all sorts of interesting findings there first at the end of generating pheromones that are sexually arousing what is required in

both species in every in both species whoa that was an interesting slip what's required in both Sexes okay what's required in both kinds um is uh right hormones in order to generate pheromones sexually arousing pheromones and all the different species look that's where the Species part was coming into that sentence what you see is males do not generate sexually arousing pheromones if they lack testosterone levels ovarectomized females women rats monkeys Etc whove had their ovaries removed do not produce pheromones that are sexually Arousing that what that of course brings up is what are some of

the chemical constituents of Thermon and this is very interesting because it brings up another one of those weird domains of neuromarketing pheromones that have sexually arousing components there's all sorts of fatty acids that play a role in it but a lot of what is sexually rousing about pheromones and different species are breakdown products of sex hormones Breakdown products of androgens in males of estrogens in females and that winds up providing some of these sexually arousing aspects of those odors what does that immediately tell you your old factory receptors have all sorts of receptors there that

could pick up on remnants of testost estone and estrogen things of that sort that makes a lot of sense what doesn't make any sense at all is the following finding which is perfume perfume in its classic form is Made out of the sweat of various animals okay except we're going to get into even worse domain here which is perfumes traditionally before getting the synthetic versions were typically made from the sweat of May animals H what's that about musk things of that sort Chanel Number Five is made from the sweat of whipped male abian cats I

kid you not and this even produced protest some years ago animal rights groups about how we should not be Perfuming ourselves with a sweat of whipped male abian cats suddenly you've got a real puzzle Along Comes synthetic perfume and the majority of them are made of synthetic versions of androgens wait a second perfume is made up of all sorts of breakdown products of male sweat isn't perfume supposed to like smell good to guys we have a deep abiding puzzle here and there is an answer for it let me survey people first off okay guys in

the Room how many of you basically think that most perfumes smell kind of appealing okay how many of you don't okay females how many of you think your basic off the rack perfume smells appealing okay well that proves something okay just to complete it how many of you don't oh okay the vast majority of perfumes are not purchased by men the vast majority are purchased by women in other words most of the Marketing decisions about what to stick in your perfumes are being marketed for people who are going to decide if it's peeling or not

people who have lots of estrogen in their bloodstream rather than androgens that is thought to be the explanation for how it is that most perfumes are derived from male pheromones yeah other thing is if I were to wear perfume it would be more so that girls think I smell good than for me think I smell good okay yes Um the strategizing starts okay so A Whole New World of potential neuromarketing here but this Taps into what are the chemical constituents of feromon what sort of information is carried by pheromones Al Factory communication between genders it

will tell you the species of the individual it will tell you their gender it will tell you whether they are gonadally intact whether they've been castrated or not it will tell you Something about their health it will tell you whether they are terrified or not have the sweat from some one or something that is terrified and as we already know it will smell differently to the amydala it will have a lot more glucocorticoid breakdown products in it and it will tell you as we know already if it's the right species if this person is related

to you final point before we then go into the specifics of what pheromones are doing to the neurobiology Of all this finally not only do you need to have hormones intact in order to generate the pheromones you need to have the right reproductive hormones on board in order to perceive them men who are castrated no longer find the smells of female ovarian um okay I'm getting ahead of myself here okay if you don't have the hormones on board if you have no estrogen and you're female or if you have no testosterone and you are male

you will not be able to distinguish the Sweat of women and men gonadally intact people can at above the chance level finally with women become far better at detecting the smell of distinguishing the smell of men versus women when they are ovulating finally finally that's not what you see when you have gay individuals gay men are better at detecting the smell of gay men than either straight men or straight women so we've gotten the first pieces of here With the pheromonal system you have to be hormonally intact to generate pheromones that are sexually informative and

to detect them what we will then transition to is what sort of information is being carried in the pheromones and what effect does it have on the neurobiology of depending on Whose pheromones you are sniffing okay so we will for more please visit us at stanford.edu