What A Rodent Brain Shows Us About Love–And Loss

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Remember that famous song Love Potion No. 9? That little bottle of elixir that smelled like turpentine, looked like India ink? Well, is there something in our bodies that turns on love, like in the song?

You know, love is a hard thing to study. My next guest works to understand the neurobiology behind love, and she does so with some unusual subjects– prairie voles. Dr. Zoe Donaldson, Associate Professor of Behavioral Neuroscience at the University of Colorado in Boulder, welcome to Science Friday.

ZOE DONALDSON: Thank you. I’m thrilled to be here.

IRA FLATOW: Can science really quantify what love is?

ZOE DONALDSON: You know, I think scientists typically dodge this question by coming up with other terms. So we talk about pair bonding, which is the scientific word for falling in love. And I think this is because, when we talk about love, it’s really this human emotion that we can talk about in literature, we encapsulate in art. And it’s pretty hard to ask how those things– literature or art, et cetera– have an equivalent in other animals.

IRA FLATOW: OK, so tell me why prairie voles are a good species to use for understanding these bonds.

ZOE DONALDSON: So prairie voles are these little tennis ball sized rodents. And they live in the prairie states– so basically from Colorado over to Western Pennsylvania, from Canada down to Oklahoma. And what makes them notable is that, whether it’s in the wild or in the laboratory, they will form these lifelong mating-based bonds.

And this is incredibly rare. Fewer than 10% of mammalian species are capable of this. We are definitely capable of this. And your more traditional laboratory rodents, like mice and rats, they fall in this more traditional category of mate and leave.

IRA FLATOW: OK, so tell me how this works. How do you study it? What do you look for in the body of the voles?

ZOE DONALDSON: So a good place to begin with this question is, how do you ask a vole if they’ve formed a bond with their mating partner?

IRA FLATOW: Very, very difficult to do that.

ZOE DONALDSON: So we try to simplify things as much as possible. And the way we do this is in a way that’s sort of equivalent to what I think of as dating. So if you go to a bar with your partner, you’re probably going to spend most of your time talking to them and not talking to someone that you don’t know.

And so we set up an equivalent scenario for the voles, where basically they can choose to go interact with their mating partner, or they can go and choose to interact with some opposite sex vole that they don’t know. And what’s really striking is that when they have formed these bonds, they just want to go over and they want to huddle with their partner. We test this for three hours, and they do this for the vast majority of the test time. It’s quite adorable. And it looks totally different from a mouse or rat, where if it’s a male and they’ve already mated with one of the females, they actually don’t even like that female anymore and they want to spend most of their time with the female they’ve not yet made it with.

IRA FLATOW: You don’t characterize this as a romantic attachment here, do you?

ZOE DONALDSON: I think that there are a lot of parallels between our romantic attachments and what we’re studying in the voles. And so a really simple one is that your attachments, especially your romantic attachments, make you feel good.

IRA FLATOW: Right.

ZOE DONALDSON: And we know that these bonds also make voles feel good. They find them highly rewarding and highly motivating.

IRA FLATOW: Is it, though, a different kind of bond you would see in voles, for example, versus a bond between a parent and child?

ZOE DONALDSON: So we don’t know the exact answer to this. But the short is that there’s a lot of overlap, and there’s some things that are different. So at the end of the day, there are certain things that we share across all of our bonds. So one of the scientific terms that we use a lot is “proximity seeking.” And that just basically amounts to we like to be around that individual.

And so this applies to pretty much all of our bonds. If we’re a toddler, we really like to be around our parents. If we have friends, we like to be around them. We like to be around our romantic partners.

But there’s also some differences. Obviously, there’s behaviors we engage in with romantic partners that we don’t engage in with parents and with friends. And so I think a big open question is, what’s shared in the brain? What’s shared across these bonds? And then what enables these distinct differences in behavior that characterize different types of bonds that we form?

IRA FLATOW: So neurologically then, what is shared across the neurons?

ZOE DONALDSON: So we think that some of what is shared is probably the basic underlying structure. So all the behaviors that we share across these bonds, like the facts that we find them rewarding, we’re motivated to seek out these individuals, we want to be near them– that’s probably a pretty common underlying architecture within the brain.

IRA FLATOW: Is there a certain neurotransmitter that you see more of?

ZOE DONALDSON: Yeah, so there’s sort of a suite of neurotransmitters, but the most famous one is oxytocin. And so this is a small hormone. It’s produced by your brain, but it actually does a whole bunch of different things. One of the things that it’s best known for is actually inducing labor.

IRA FLATOW: Wow.

ZOE DONALDSON: Yeah. So they give pitocin, which is a synthetic version of oxytocin, which induces labor. And that was one of the first things that was learned about oxytocin as a hormone was its function in reproduction.

And then a few scientists thought, hey, you know what? Rats do this weird thing where when they’re a virgin and they’ve never given birth before, they don’t like pups. But as soon as they’ve given birth, there’s this switch in the brain where they just desperately want to take care of their pups.

And there’s this great series of experiments. We call them the “puperator experiments,” where they give a female rat who’s just given birth, they give her a little lever. And she can press the lever, and they’ll deliver a pup to her. And she’ll just keep pressing this lever until she has a mountain of pups so big that she couldn’t possibly take care of all of them.

IRA FLATOW: No kidding.

ZOE DONALDSON: She’s super motivated. And it’s this shift in behavior, and that shift in behavior to wanting to take care of pups is mediated by oxytocin.

IRA FLATOW: Is this love potion number nine, oxytocin?

ZOE DONALDSON: It’s part of the love potion. I would say that the love potion is actually really complex. So in addition to oxytocin, you also have dopamine. You have another hormone called vasopressin. There’s probably a role for serotonin.

So it’s a really complex mixture of things that’s happening in the brain. Oxytocin is essential. But you can’t just throw oxytocin at someone and have them fall in love with you.

IRA FLATOW: Wow. This is really interesting. I know you also studied prairie vole breakups. Do they have broken hearts?

ZOE DONALDSON: They do, yeah. So prairie vole broken hearts look a lot like human broken hearts. They show a lot of different types of behavioral distress when they’re separated from their partner. They show behaviors that are reminiscent of depression.

And then one of the areas that my lab has been really actively working in is trying to figure out what is special about these breakups, or even the loss of a partner, compared to these other things like depression? And we think the key to this is actually yearning. So yearning is something you see only after a breakup or after the loss of a loved one, and it’s something that differentiates those losses from, say, just general depression.

So one of the things we see in the voles is that they’re actually a little bit more motivated to seek out their partner if they haven’t seen them in a while. So this is the whole “absence makes the heart grow fonder” idea.

IRA FLATOW: Wow. Who would think that animals had the same kind of feelings that humans did? Did you? Is this surprising to you when you studied this?

ZOE DONALDSON: This is actually why I fell in love with the voles.

IRA FLATOW: Really?

ZOE DONALDSON: Yeah. This is what motivated me to become a social neuroscientist and to start studying attachment. Because as humans, if we think about the most important things in our lives, we usually start talking about having kids, getting married, loss of a parent or someone else who’s incredibly important to us. And so I thought, I want to study these things that we find fundamentally important.

And then I started thinking how we could do this, and it was clear that mice and rats have some real limitations since they don’t form these bonds. And the more that we learn, the more I’m impressed by the conservation of how our brain works. There is a blueprint for the brain, and so it’s not totally surprising that these complex emotions that we feel as humans have some basic representation, even in other species.

IRA FLATOW: So you think there’s a correlation between what’s going on with the voles’ brain and what’s going on in our brain?

ZOE DONALDSON: Yes, that’s the premise to all of our research. Because the idea is that what we discover in the voles may help guide us to develop new therapies. And so there’s a couple of directions this could go. One is that the vast majority of neuropsychiatric disorders throughout the life course can affect our attachments. And this begins even early in life, and manifests in things like autism spectrum disorders.

Also, if you think of things like schizophrenia and depression, you can have a reduction in your attachments and how much social reward you feel. And later in life, you have things like neurodegenerative disorders, which have huge impacts on relationships. And also, people start displaying sort of inappropriate behaviors in relationships, or even just social withdrawal.

IRA FLATOW: So why are we spending so much time studying rat brains about what’s going on in our brains, and not vole brains?

ZOE DONALDSON: So rats and mice are excellent models for many, many things, and there’s parallels with humans. If you want to understand how the brain makes your arm move, or if you want to understand just basic anxiety states, or hunger, or thirst, we share those with rats and mice. What we don’t share with rats and mice is our really complex socioemotional behaviors.

IRA FLATOW: All right, so what is there yet to be studied in the vole brains, comparing them to us, that you would like to study? And I’ll give you my blank check question I give a lot of scientists. If you had all the money in the world and you could spend it on anything to learn more about what you want to know, what would you spend it on? What do you want to know?

ZOE DONALDSON: So I really want to know, fundamentally, how are these bonds encoded in the brain– but also, how are they plastic at the same time? So what unique features of our brain make it so that we can form these bonds, but we can also lose these bonds and we can adapt to that loss. And I want to fundamentally understand, what is it about our neurons– and their firing properties, and the different inputs they get from hormones, et cetera– that enables this incredible complexity?

And this complexity is something that defines us as humans. If anything, we take what voles can do and we just basically add steroids to it. We have terminology like “frenemy.” I doubt the voles have frenemies. But the complexity of the social behavior that we can study in voles compared to other models, I think, really just gives us a lot to work with and a lot that can tell us something about the human condition.

IRA FLATOW: Very interesting. One last question for you. So after this study, do you believe in life after love, as Cher would ask?

ZOE DONALDSON: Oh, absolutely. So the vast majority of us will lose someone in our lifetime. And for about half of us, we will lose a spouse. And so the idea that there isn’t life after love is a pretty depressing idea.

This is the plasticity that I mentioned. This is why I’m so fascinated with it, because we do have the ability to integrate these losses. It’s not like we forget the people that we lost, but we have to rework the memories that we have with them and what they mean to us. And so one of my favorite terminologies is actually from a clinician that I work with who says that those memories have to go from painful to bittersweet.

IRA FLATOW: Yeah. Wow. What a way to end our conversation. I have learned so much today. Thank you for this lesson on love. Dr. Donaldson.

ZOE DONALDSON: Thank you for having me.

IRA FLATOW: Dr. Zoe Donaldson, Associate Professor of Behavioral Neuroscience. That’s at the University of Colorado in Boulder.

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