That Neuroscience Guy - Season 4 Finale - The Neuroscience of Sex

Episode Date: April 12, 2023

Sex is a complicated topic: it's a mix of libido, attraction, social interaction and motivation. To cap off season 4, we're diving into the neuroscience of sex, why we want to have it and what's going on in the brain while we have it. 

Hi, my name is Olof Kregolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. Well, we've had tons of user requests for the neuroscience on this topic, and I have to admit, I'm feeling a little bit anxious about covering it. But for the last episode of season four, I thought, what the heck? We've had people asking for three seasons now. So it's a tough topic to cover, but I'm going to keep this as clean as I can and general rated. But today it's all about the neuroscience of attraction and sex. So the story of the neuroscience of sex starts with sex drive, which is otherwise known as libido or lust.

Libido is one of the oldest human motivations, and it's associated with the natural instinct to reproduce. At a low level, this is where a structure such as the hypothalamus comes in and plays such a crucial role. When we humans reach an appropriate age, hormones are released and we begin to feel the essence of libido. Now, if we think back to what we've learned about the hypothalamus, it's a midbrain structure that helps regulate the sympathetic and parasympathetic nervous systems. So speed up the heart rate, slow down the heart rate, increase sweating, decrease sweating. But it also is tied

to a lot of behaviors that are associated with sex, the desire to reproduce the attraction you feel to someone else. So this crucial midbrain region plays a big part in this story. Now, of course, this is different for everyone in terms of how our brain interprets these signals. And some people never really feel this kind of motivation, but the majority of adult humans experience libido and thus feel the need to reproduce. Basically, it starts with puberty when our bodies begin to change and mature. And these changes are what we call sexual maturity. And that's brought on by the release of hormones. We'll come back to those hormones in more detail a bit later. But when you get to that point, that's when our bodies begin to think maybe we should get there.

And it's triggered by this release of hormones from the pituitary gland, but controlled by the hypothalamus. Now, it's crucial to realize that there's other brain regions that play a role here. Of course, our old friend, the amygdala, adds to this story. We've talked about the amygdala so much. I joked one time we should call this the amygdala podcast. But if you remember, the amygdala is one of the key emotional centers in the brain. And when we start to feel this urge to reproduce, the amygdala is going hyperactive. Strong emotional responses to things, and that plays a key role in shaping our behavior.

And the prefrontal cortex plays a role too. Basically, the prefrontal cortex sort of works to regulate this whole cycle and try to keep it in check and act rationally in our pursuit of a partner. And this is actually why puberty can be so hard for teenagers. Hormones are being released. The amygdala is firing away like crazy. But the prefrontal cortex is not fully developed. And if you remember that the basic way to think

about brain development is from the inside out and the back to the front. So the last region of the brain to develop is the prefrontal cortex. In teenagers, it's typically not quite there. And this is why the behavior we see in teenagers when it comes to sex is there. So we've established this underlying primary drive, this desire to reproduce. Well, what comes next, I guess, is attraction. We need to find a potential partner if the goal is reproduction. We talked about love on a previous episode, so I'm not really going to go through the whole love thing, but I'm going to focus more on attraction. But it's pretty simple. Attraction

basically comes down to the dopamine system and the norepinephrine system and how they respond. Much like on social media, when we encounter someone we find attractive, the midbrain dopamine system fires and these little spikes drive our motivation. This is like akin to when you get those likes on Facebook or Instagram. Those trigger those little dopaminergic responses that make you want to engage in that behavior more. Well, that's the same sort of process that underlies attraction. And basically, the chemicals that are being released, they make us giddy. Like, they make us energetic, euphoric.

They can lead to, you can control your appetite. They can decrease your appetite and even create insomnia so much that you can't sleep because you're just thinking about things so much. Norepinephrine really plays a crucial role. And I want to highlight that we talked a bit about dopamine just now, but it also plays a large part of our fight or flight response. And it basically dials up our brain and keeps it in gear and we're stressed and keeps us alert. And if you actually look at this through imaging, and there is some imaging done on this area, you basically find that this release of dopamine and norepinephrine is associated with the reward

centers of the brain, like the ventral tegbenol area, the caudate nucleus, the ventral stratum. They're just firing like crazy when people are shown a picture of someone that they're attracted to, compared to when they're shown someone that they're not attracted to. So the brain has this sort of system that's driven by neurotransmitters and includes a couple of key brain regions that controls our attractive behavior. Now, it's important to note that what we find attractive is a learned experience. And this is the nature versus nurture thing.

Typically, you could almost say we're brainwashed in modern society about what we're supposed to think is attractive. And luckily, I'd like to think it's slowly changing, but there's still a lot of stereotypes out there. But we learn these things, and then our brain typically responds to something that we feel is attractive. But I can't highlight the role of individual differences enough. What's attractive to one person might not be attractive to another person. Now, when I started doing the research for this, because this is a bit outside my primary research area,

other than a little bit about the reward system, I'm just fascinated how this whole process of attraction and sex is ruled by chemicals within the brain. You know, lust and this sort of desire to reproduce is tied to hormones like testosterone and estrogen. That attraction thing, as we said, is tied to dopamine and norepinephrine. And even attachment, when we find a partner, is tied to the release of oxytocin and vasopressin within the brain. So basically, this desire to reproduce is triggered by sex hormones, okay, released by the ovaries and the testes and that goes up attraction is this dopamine thing and it's tied to the hypothalamus triggering the release of this and norepinephrine as well and like i said the hypothalamus also controls attachment by the

release of oxytocin and vasopressin but don't forget the prefrontal cortex sitting there trying to regulate and the amygdala firing away going, yes, this is what we want to do. And what's interesting is that the release of these neurotransmitters and chemicals are actually tied to when there's too much in the system. So if you have ideal levels of dopamine and oxytocin and vasopressin and serotonin, that's when you get behaviors like lust, which is perfectly natural, this desire to reproduce, attraction itself and attachment.

But if you have too much dopamine flowing through the system and too much serotonin and too much oxytocin and vasopressin, well, that's where you get irrational behaviors, binge eating, possibly alcohol or drug abuse. It's thought to underline adultery even, that the release of too much of these chemicals drives us to be promiscuous and even tied to

jealousy in the sense that when we get jealous of someone else, it's because we have too much of these key neurotransmitters floating around within us. Now, I guess that gets us to sex itself. now i guess that gets us to sex itself it's incredibly hard to study sex from a neuroscience perspective for what i hope are obvious reasons but some studies have generally sexual behavior is regulated by a bunch of subcortical structures such as the hypothalamus which we've mentioned the brainstem and spinal cord and there's several cortical areas activating as well. And basically, this creates a system that is activated during sexual intercourse. Dopamine's still there, norepinephrine, and they're playing a key role as sex is happening. And then there's other systems as well that are releasing things into the bloodstream

and this complex sort of orchestra to control sexual behavior. Now, some studies have actually managed to scan the brain during sex itself. And it's interesting because they basically, like I've just sort of said, found the brain light up completely. The sensory system is activated for obvious reasons because there's a lot of sensation happening. The motor system is activated to control the behavior itself. The reward system is firing because you're engaged in a rewarding activity. The frontal parts of the brain, the prefrontal cortex are engaged. Like I said earlier, the brainstem.

But it doesn't stop there. The nucleus accumbens, the insular cortex tied to emotion and reward, the anterior cingulate cortex, which is tied to action selection, the orbital frontal cortex, which is back to the prefrontal cortex controlling things, the right angular gyrus, the paracentral lobule, the cerebellum, the hippocampus, because memories are being formed, the amygdala, again, the emotional response. So much of the brain is activated during sex. So the process is pretty well established now in terms of these three key steps. What's interesting is there's actually

some fairly recent research that basically suggested a single molecule called kispeptin and the release of kispeptin basically helped coordinate this whole thing together, this whole process of being attracted to someone wanting to reproduce and the act of sex itself. of being attracted to someone wanting to reproduce and the act of sex itself. So the neuroscience and neuroanatomy of sex, the take-home message is it involves most of the brain, some regions more important than the others. The key ones, the prefrontal cortex, controlling behavior, the amygdala, emotional responses, and the hypothalamus causing the release of these chemicals we've talked about, sex hormones in terms of the desire to reproduce, attraction, dopamine and norepinephrine,

and then attachment, the release of oxytocin and vasopressin. So there you have it, the neuroscience of sex and attraction. And that is the last episode of season four. We're going on a break for about a month. It's about the middle of April right now. We're going to be back in the middle of May with season five. We're not going anywhere, but Matt and I have had a long year and we both need a bit of time off. So my apologies, but we're going to be off the air for about four weeks ish. We're hoping for in the interim, send us your ideas for season five. You can follow me on Twitter, at thatnerosagguy, and DM me some ideas.

This episode and so many in season four have been driven by you, the listener. And of course, check out our website. I've been promising new t-shirts forever. I'm actually going to New Zealand tomorrow, and when I'm down there, I'm going to have a bit of free time. And I intend to come up with at least three new t-shirt designs. So if we start season five without three, I don't know.

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All of the money goes to students in my lab. And so you're supporting neuroscience research. I can promise you, you're not supporting me. I won't release my income tax forms, but if you can trust me, I'm not taking any money from Etsy or Patreon for myself. It all goes to students like Matt in my lab. And last but not least, thank you so much for listening. Please subscribe to the podcast. It helps so much and it motivates us to keep going.

So thank you for listening today and for all of the previous four seasons. Like I said, we'll be gone for four weeks, but we'll be back for season five around the middle of May and we'll bring you more of the neuroscience of daily life. My name is Olive Krigolson and I'm that neuroscience guy. I'll see you soon.