Hey Currency Collective!
Welcome to this weeks newsletter! We’ll be exploring the reasons behind why sex can’t be casual.
The Brain Treats Sex as a Bonding Experience
And evolutionarily, this totally makes sense. In a social species that’s interdependent - relying on others to care for us in times of need - we would want sex, something that produces offspring, to be a bonding experience (1).
And based on the neurotransmitters and brain regions involved in adult sexual relationships, it seems like this evolved from the same system that leads to mother-infant bonding. For example, the ventral tegmental area, responsible for motivational behaviors and heavily influenced by dopamine pathways, is involved both maternal and passionate love. In the same way nature would want to ensure a parent cares for their child, nature also wants to make sure both caretakers are looking out for one another.
For this reason, sexual interactions don’t just feel good, but they trigger reward-based learning and emotional attachment mechanisms.
Sex on the Brain
Sex triggers a potent neurochemical cocktail:
dopamine
In the nucleus accumbens of male rats, dopamine spiked in the lead up to and during sex (2). The nucleus accumbens, located in the ventral part of the striatum, is heavily responsible for pleasure, motivation, and learning. This is part of the system responsible for us learning what results in us being rewarded and what doesn’t. It’s heavily involved in addictions for that reason. This is also why it’s difficult to keep sex casually – sex is literally triggering you to become addicted to that person.
And that spike in dopamine happening before sex is the anticipatory dopamine. We start to anticipate the sex with that person (3). We learn to anticipate it. And when we don’t get it, it can feel disappointing.
oxytocin,
In humans and animals, we see that oxytocin release is increased in men and women during orgasm (4, 5). Oxytocin is known as the ‘love hormone’ or ‘cuddle hormone’ for good reason; it’s heavily involved in attachment and bonding, and critical in early stages of romantic bonding (6). We naturally start to become bonded to someone who spikes our oxytocin, which is what’s happening during sex. Because it’s also involved in social cognition and empathy via interactions with the amygdala, we typically start to have feelings, even if just sympathetic, to those we are sexually involved with (6).
*Important Note: Oxytocin and dopamine interact with each other. This results in the link between the neural representation of the partner with the social reward of relationship and sex (7). This learned association then creates a bond between the pair. Even if the pair is determined to keep the sex casual.
vasopressin,
Vasopressin is increased during sexual arousal but usually returns to baseline before orgasm (8). It’s usually associated with aggression, territoriality, and mating. However, it also facilitates pair bonding, which is thought to be through it’s role in partner preference (9). It seems especially important in male animals to promote sexual activity and parental nurturing (10).
However, the effect of this hormone in relationships isn’t fully established, and differences between the sexes remain unclear. It seems likely that it’s involved in protectiveness, maybe jealousy, and influences the consistency of sexual interest in a relationship (11).
Either way, this hormone is being released during sexual arousal and probably explains why that person you’re ‘just trying to sleep with’ has started to make you feel jealous (11).
Syncing our Nervous Systems
I’ve talked about this concept in a few previous articles - our nervous systems sync with those who are around us. This is why anxiety from your family can feel contagious and make the holidays difficult.
But it’s also why we can take control of a situation and shift the emotions.
It can make us more attractive to others and make us feel more connected with others.
Well, that’s still happening even if you’re ‘just’ sleeping with someone. The whole point of this synchrony is to make us feel more connected. So, naturally, feelings will start to become involved when you’re spending a lot of time around someone.
Sex Activates Your Attachment System
The same neural circuitry that governs attachment in childhood (the amygdala, anterior cingulate cortex, insula, and orbitofrontal cortex) lights up during sex (12). In fact, individuals with different adult attachment styles will have different brain-level responses to sex (13). For example, someone with a fearful attachment style will have lower brain activity in response to sexual images in comparison to individuals with secure attachment styles.
This also leads to a different emotional response after sex (14). Individuals with attachment anxiety typically report lower satisfaction and more guilt following sexual encounters.
Therefore, sex can amplify our attachment style patterns – making us crave reassurance if we’re typically anxious or forcing ourselves to become detached and aloof if we’re normally avoidant.
Post-Sex Cognitive Dissonance
When our brain and body our releasing all the signals for bonding, but we’re still trying to tell ourselves it’s casual, we start to feel internal conflict. This mismatch activates the anterior cingulate cortex (15), which detects “errors” or mismatched expectations. We try to rationalize (“I’m fine,” “It meant nothing”), but our body is telling us something else.
This often leads to rumination, checking your phone, or replaying moments; all manifestations of dopamine-seeking closure.
My final note is that the state of science up until now means a lot of research has only been done on men. We are of course seeing this change, and there are now studies looking at differences between the two sexes. There do appear to be a lot of similarities, especially in the overall wiring of different neural circuits, and chemicals being released. But differences are appearing, which I touched on already with vasopressin, and more will probably come up as we look (16)!
So, this will probably need to be revisited and revised in a few years!
Until next week,
Nic x
References
(1) https://pubmed.ncbi.nlm.nih.gov/37372130/
(2) https://pubmed.ncbi.nlm.nih.gov/2176121/
(3) https://pubmed.ncbi.nlm.nih.gov/1840012/
(4) https://pubmed.ncbi.nlm.nih.gov/3782434/
(5) https://pubmed.ncbi.nlm.nih.gov/3024195/
(6) https://pmc.ncbi.nlm.nih.gov/articles/PMC2748133/
(7) https://pmc.ncbi.nlm.nih.gov/articles/PMC10295201/
(8) https://pubmed.ncbi.nlm.nih.gov/3654918/
(9) https://pmc.ncbi.nlm.nih.gov/articles/PMC3602142/
(10) https://pmc.ncbi.nlm.nih.gov/articles/PMC9213575/
(11) https://www.tandfonline.com/doi/pdf/10.1080/14681990412331297974#
(12) https://pmc.ncbi.nlm.nih.gov/articles/PMC5675825/
(13) https://pmc.ncbi.nlm.nih.gov/articles/PMC4852297/
(14) https://pmc.ncbi.nlm.nih.gov/articles/PMC9916622/
This is a really interesting breakdown of the chemistry. What I'd add is that "casual" is never really about the sex - it's about the relational aspect. Our biology relies on reliable connection, we've just gotten better at pretending that isn't the case because we're not raised on a diet of vulnerability. I think the more honest question isn't "can sex be casual?" but "why do we need it to be?"... Thoughts?
Interesting how the attachment styles impact our experience’s / it feels like some people are incredibly connected during ‘casual sex’ but get to a point where they kind of drop out of being able to meet altogether. It has felt so hard to understand the incongruity between the intimacy and disappearance.