Ep 105: The Hormones Behind Bonding, Relationships, and Sex
Andy:
Normally it's nice to start by just kind of asking you a little bit about your background and about how you got into this field, how you got into the really interesting research that you're doing, and then also how you got into writing about it.
Dr. Larry:
I'm a neuroscientist interested in the brain mechanisms that give rise to social behaviors, parenting behaviors, love, all kinds of social interactions. And I got started because I grew up on a farm and there were lots of animals around and I could see all of these animals, these different species of animals had different instincts. They weren't taught how to behave, who to partner with, how to take care of babies or things like that. Those kinds of instincts were somehow ingrained into their brain as their brain developed. And I realized that was because they had genes that told their brains how to develop. So I thought it was really cool to be able to try to understand how you can go from like genetic instructions in your chromosomes to the development of a brain, into an organism that knows how to behave in the way that that species is supposed to behave.
Dr. Larry:
And so, after going to college, I went to graduate school and I studied, actually, the sexual behavior in lizards and homosexual behavior in lizards. There are lizards that engage in homosexual behavior and I spent several years just trying to understand, what is different in the brain of a homosexual lizard versus ones that are heterosexual lizards. But that experience, I just learned more about the brain and got more interested in, really, diversity. We don't all behave the same, we don't have the same motivations.
Dr. Larry:
But also like the strength of the parenting motivation, motherhood. That's something you can just look around and all animals as soon as they have babies, if they're mammals (or birds), they take care of those babies. So, I wanted to understand how that motivation arises, but also why is there diversity in different species.
Dr. Larry:
And when I talk about diversity in behavior, if you can think about it in terms of dog breeds. You've got pit bulls, you've got basset hounds, you've got chihuahuas, you've got all these different dogs, they're all the same species, but they have different personality traits. And so you can understand that from the brain. But also from a more practical perspective of, why is this important? Being able to form bonds and relationships and just to be able to read each other's emotions and things like that, is really important for our well-being and being able to survive in society. But those are also the things that go wrong in disorders like autism.
Dr. Larry:
So, it turns out that the work that we've been doing, which we'll talk about later on these little voles, is giving us insights into how we might improve social functioning in diseases like autism. So that's why I'm in the department of psychiatry at Emory.
Andy:
And then why voles? You went from lizards, and you thought that was kind of interesting, and then something attracted you to the vole?
Dr. Larry:
So why voles, well, it's pretty cool. Most mammal species, males and females, mate and then after mating, the male splits and the female goes off and has her offspring by herself. There's no emotional connection between the two.
Dr. Larry:
But in voles they're socially monogamous, which means they're very much like people. When a male and a female prairie vole comes together, the male will court the female. If the female likes that male, she'll let him mate. And when they mate something magic happens in their brain, so that from then on those two guys want to be together. They nest together and they raise their offspring together, generally for the rest of their life.
Dr. Larry:
Not all prairie voles do that, if you look in the wild about 60 to 70% of males have a female partner that they're living that lifestyle. About 30 to 40% of the males just remain bachelors all their life, they decided they don't want to settle down and have a nest.
Dr. Larry:
But even though they're monogamous, very few are completely sexually faithful. Sometimes they do have an affair, an extra pair mating. But they will always come back to their partner. So to me, it just seems like that's a really good model for human beings.
Andy:
Wow, yeah. Sounds familiar!
Dr. Larry:
But the other thing about the voles is that there's a different species of vole that looks just like prairie voles. If you saw them in your backyard, you wouldn't be able to tell them apart.
Dr. Larry:
These guys are loners. They're called meadow voles and they just don't care about being around others. So if you think about kids, some kids are very social, they got lots of friends.
Andy:
Totally, yeah.
Dr. Larry:
Others, they just don't need that or they don't know how to achieve that. Meadow voles are like that and they mate and have babies just fine. But the males does don't stick with the females, the female doesn't like the male after that. She has her babies and she actually abandons her babies two weeks after they're born—they’re able to survive, but, it's just different strategies. And both of those strategies work in nature.
Andy:
They're still alive and kicking as a species.
Dr. Larry:
They're still around. Because of that, these species that are so closely related, look the same, but they have this very different kind of social behavior. I thought this is a great opportunity to try to study in the brain what makes some animals be able to have these close relationships and bond. And others, why that's not so important.
Andy:
So I found a lot of really interesting things in your book based on your research and just on other research that you mentioned from other people, and you have great stories in here. One thing that I kind of wasn't aware of is you talk about this sexually dimorphic nucleus. And so that's somehow is what's differentiating between the male and the female brain, that was like one of the things that they first noticed.
Dr. Larry:
Yeah, I wouldn't say that that is the cause of all the differences between sexes in their behavior. But this was sort of an early discovery probably around 1980 or maybe in the seventies, if you take male and female rats and you stain the brain so that you can see the different brain areas. There is a part of the brain, the sexually dimorphic nucleus that is about four times larger in the male brain than in the female brain.
Andy:
Interesting.
Dr. Larry:
And so that was at the time, kind of astounding finding, that there is a real physical difference in a male and female brains. And that kind of research has continued and there are many now more detailed examples of sex differences in the brain in terms of wiring or different aspects. But it's interesting that this particular one, this is sort of the first one that we'll study the most.
Dr. Larry:
It was found that it's not really that it's genetic, it's that when males are young, if we're talking about rats here. Before they are born, their testes are very small, their testicles are not active. And the female ovary is not active at all, it's not producing any steroids.
Andy:
Sure.
Dr. Larry:
But right around the time of birth in these rats, the brain starts pumping out chemicals that activates the testicles. Testicles starts to creating testosterone. Testosterone is a steroid hormone that then gets in the brain and it organizes the brain at that early stage and it changes the way that that brain responds to hormones for the rest of the male's life.
Dr. Larry:
So it's that surge of hormones that comes from the developing testes in males that helps shape the males brains and that's partly why males, snips and snails, and puppy dog tails. Males have different kinds of behaviors from that early kind of surge. In humans that surge actually happens before the infant is born, but it causes some real sexual differences in the brain. And of course, there's also many cultural differences that add on top of that once a child is growing up, whatever particular society and culture they're in. The cultural differences can add to that, but not all the differences between boys and girls are learned.
Andy:
So this is part of what you refer to as the organizational hypothesis and it's this idea that the brain is bathed in those kinds of hormones in utero. And that is what starts to create these differences in the brain. And then you have some really interesting stories in here about people who are raised as different sexes or have like different situations in their lives that like really help you to understand how important that early phase is, where the brain differentiates, I guess.
Dr. Larry:
That's right. Yeah, so there are cases of ambiguous genitals where clear when the baby is born, whether it is a penis or a clitoris. Because those two structures come from the exact same structure developmentally. At early stage in development, the penis and the clitoris look identical and it's only the testosterone that comes from the testicles, which I already mentioned as going into the brain and changing things in the brain. It also goes to the genitals to turn that organ into a penis.
Dr. Larry:
But in some cases, there's variation in that, it's not like a switch. So if for some reason the infant doesn't see much testosterone, it doesn't grow a robust penis. Then in the sixties or seventies, there was a lot of work where they were doing gender reassignment. Where they would do a surgery and then that child would be raised as a female if it was a boy.
Dr. Larry:
But that child still had testosterone early in its life. And then when they became adults, even though they were raised culturally as a female, when they became adults, then suddenly their identity was male and they wanted to change.
Andy:
It didn't work, yeah.
Dr. Larry:
There's even a disorder in the Dominican Republic where a certain percentage of the children are born as the parents think they are females and they are raised as females, because they have a deficiency in an enzyme that helps make this testosterone and DHT, the active form of testosterone. And so those individuals actually appear to be female, but when they get to be a teenager and they going through puberty, they have so much of this brain hormone that is controlling the testicles that they secrete enough of testosterone, that they then become masculinized. And then they sort of changed their sexual identity. Just think that this is ... can be up to like 10% of the population in this Island population. So as I mentioned earlier, I'm interested in diversity in animals, but you can see the same kind of diversity in humans.
Andy:
Yeah. I thought that story was so interesting in the book about the Dominican Republic and yeah, ultimately where you guys go with it and how you explain it all, then it really makes a lot of sense. And it really helps you understand the concepts, I think, when you see that in context.
Andy:
One thing I also thought was really interesting is this difference in attraction, female attraction at different parts of the menstrual cycle. And you talk about, maybe it might explain why some women become entangled with bad boys. So I guess this is something that I was not aware of when I was a teenager, but that I think I would want to know. And so I guess ... and especially, I'd want to know if I was a female teenager because it's really affects your life, I guess. And so could you talk a little bit about what that is and how that works?
Dr. Larry:
Oh yeah, so if you think for most animals, let's talk about animals for a second before we talk about humans. Because we are an animal and our behavior was sort of shaped in our evolutionary history. But for animals like cats and dogs and rats and mice, females are absolutely not interested in sex until they're ovulating. Sex is for ovulation, so sexual attraction only happens when the egg is ready to be fertile. So if you think about cats, anybody who has a cat in heat, they know how different their sexual motivation changes from when they're not in heat to when they're in heat.
Dr. Larry:
Because what happens is you have these hormones in the female, estrogen and progesterone that is secreted by the ovary, but not secreting very much until the egg is about to ovulate. And at that point, those hormones go into the brain and suddenly change that motivation of that cat. So if she's in heat, she'll do just about anything to get out of that house and to find a Tomcat. And so that's animals.
Dr. Larry:
Humans are quite different, very different from that. We are not totally enslaved by our hormones. Females, their reproductive desire is not totally defined by what stage of their cycle they're on. But human females do have this same oscillations in estrogen and progesterone and it's related to their menstrual cycle. So it makes sense that maybe there are some changes in human females sexual desire or way of thinking that may influence sexual choices. Some of this literature may be not agreed by everyone, so I'm not going to state this is fact, but I will tell you that there are literature that reports this.
Dr. Larry:
That women when they are at the time where they can be fertile, they seem to be more interested in talking to, flirting, more into entice the bad boys. Authors will often say this is a chance to find someone who has so strong genes. But they're not, they're more interested in someone who would be apparently like a good dad or something like that, not the bad boy. And if you think about from the perspective of if we were like animals, then it kind of makes sense, you might choose something different.
Dr. Larry:
And so that's the story and even there are ... we talk in the book about the case of strippers, how they make more money. There was a study that showed that strippers make more money when they're ovulating.
Andy:
Like a lot more money, they get like twice as many tips or something--you reported the dollar amounts in here, it's crazy.
Dr. Larry:
And that's probably not because the men can somehow sense that they're ovulating.
Andy:
They don't know, yeah.
Dr. Larry:
But maybe those women are acting differently at the time they are ovulating. So for example, there are other studies that we mentioned where women at certain times of their cycle are more likely to buy or wear really sexy high-heeled shoes or no clothing, things like that. But like I said, that literature, some people contest that and, I'm not exactly sure how much of that is really true now with several years after writing the book, so I'm not trying to promote that idea.
Dr. Larry:
But there are studies out there showing that kind of thing and maybe parents can make up their own mind.
Andy:
It's definitely interesting and it's definitely something to think about and know about. And yeah, to always be mindful of and consider how things like that can affect us. And I guess it's just an example of like how important biology is and what's happening in our body, and like the whole picture is on our decision-making process.
Dr. Larry:
Absolutely, even in ... well in both boys and girls, pre-puberty versus post puberty, there is a huge difference. And that's not just because someone told them that they should be doing this, that certain topics should be occupying their thoughts. This is real changes that are happening in the body that are just ... these hormones are getting into the brain causing transcription, changes in your genes, in different brain areas. And all kinds of things happening in the brain and it's a real phenomenon.
Andy:
Where do fetishes come from and how do they develop?
Dr. Larry:
Yeah, this is another interesting story that we talked about in the book. And this is really about the linking of the brains sex experiences in reward systems, to other things that are around in the environment. So, as you know, sexual behavior is really, really rewarding, it releases a lot of dopamine and that dopamine activates the reward system.
Andy:
Feels good, yeah.
Dr. Larry:
Yes. And at that time was a lot of seeking of activation of the reward system, during teenage years. But so we talk about a study, and again, this is not my study, I'm not trying to promote this idea. But there are people who have said that maybe fetishes for things like shoes, which why would someone have a fetish for a shoe? That has nothing to do with sexuality.
Andy:
Right. Yeah, yeah.
Dr. Larry:
But one of my colleagues, Jim Pfaus, formerly at Concordia University, made the proposition that maybe teenage boys when they first have their first sexual experience through masturbation, maybe they're in a place where there are shoes, the closet or something like that.
Andy:
Right, just gets kind of linked in there somehow.
Dr. Larry:
Yeah. So basically it's this--and we talked about this later in the book in terms of how we fall in love. We fall in love because we're having a good, rewarding dopamine releasing experience with a person, with a certain kind of hair and a certain kind of face. And that person, we develop a fetish towards that person. And so that's a natural process of bonding.
Dr. Larry:
And maybe a fetish is just a simpler version of that where you--
Andy:
It's when it gets like directed towards something that's not a person.
Dr. Larry:
Right. It's kind of like when drug addict, if they're using a drug with a certain, say glass pipe. Then suddenly that glass pipe gets them aroused--in terms of the drug seeking behavior, not sexually. And there's no reason [the pipe] should [do that], except that in their brain it is now associated that with that dopamine.
Dr. Larry:
And so, Jim has this very interesting idea that fetishes arise because whatever the subject of the fetish is as something that the person has been around during the early sexual experiences from perhaps masturbation.
Andy:
Yeah, even including masturbation. Which I think is so interesting and parents don't want to talk about masturbation with teenagers, it's awkward, I get it. But I think it's such a good example of how it's important at like whatever your teenagers are doing, they're masturbating right now. And how are they doing that? And that actually matters and that could be creating some of these things. There could be a weird fetishes getting created just because they're forced to like masturbate in like in a closet because they feel like embarrassed or ashamed about it because it hasn't been talked about or whatever, I don't know. But I think having the conversation and bringing it out in the open is good.
Dr. Larry:
Certainly, masturbation is a natural process that very large percentage of people do during development. And people should not be made ashamed of it because that creates a lot of confusion in the brain.