Attraction. Desire. Devotion. Dedication – just some of the vital characteristics needed to create a long-lasting love. However, unlike the ‘sugar, spice and everything nice’ ingredients required to create a girl (thanks for that super accurate recipe Powerpuff girls), aspects of loving feelings can be described by actual real-life chemicals. You constantly hear of two individuals having “good chemistry” when entering into a blossoming romance, but have you ever thought about what these chemicals are and how they act to induce a love-struck state? The chemicals underpinning love have the ability to make you weak at the knees, delusional and irrational, but also promote unwavering trust and commitment. Technically, a similar mix of emotions could be artificially induced by the administration of a concoction of ‘love chemicals’. Some companies have even developed a ‘liquid trust’ spray to blindside consumers into signing their money away and instil confidence in big business. But can something so deep and meaningful really be mimicked?
The neurological mechanisms which summate to L.O.V.E have been extensively studied in the monogamous mammal; the prairie vole. That’s right, there are cute lil voles out there who hold lil hands and have lil families and live happily ever after (like a real life Sylvanian family). The prairie vole forms a ‘pair bond’ with their partner and this normally lasts for life (actual relationship GOALS). Prairie voles with a pair bond will co-parent by raising their pups together and will rarely move on if their original partner dies. So legit, how do they have this dedication? What is their recipe to a long-lasting relationship?
Some of the chemicals found to be fundamental to prairie vole commitment are oxytocin, arginine vasopressin and dopamine. These neuropeptides are also found in humans and it is thought that their interactions with their neuronal receptors in specific brain regions and with each other augment that all-consuming love the great play-writes describe. So, in order to learn about why Romeo died for Juliet, let’s get down to how these particular love chemicals act in your brain.
Oxytocin is a neuropeptide produced in a brain region called the paraventricular hypothalamus, a region important for regulating autonomic functions, and it is released by the pituitary ‘master hormone’ gland. Oxytocin acts at oxytocin receptors (OTR) on neurons. In the praire voles, these receptors are found in high numbers in the caudate putamen, nucleus accumbens and prefrontal cortex; areas associated with the release of the ‘reward’ hormone dopamine (more below).
Oxytocin is implicated in both maternal and romantic love; being released during breast feeding to enhance the mother-infant bonding as well as during sexy time with a partner, especially in women. This is unsurprising as both parental and romantic relationships require the formation of a strong bond which enables you to take risks for the sake of your partner. In the prairie vole, infusion of oxytocin into the brain of a female prior to mating leads to quicker formation of the pair bond with their partner, suggesting this hormone plays a pretty important role in solidifying the long-term aspect of romantic relationships. If OTR’s are blocked in the prefrontal cortex and nucleus accumbens of female prairie voles, the pair bond cannot be made and oxytocin knock-out mice (containing no oxytocin) fail to recognise individuals they have previous met. This info suggests oxytocin's reaction with specific brain regions augment the development of a loving bond whereas the general action of the hormone across other brain regions is important for recognising the individual with whom you have made that bond. Because, let’s be honest, it would be pretty hard to identify your partner fo’ life if you couldn’t tell them apart from all the other ‘fish in the sea’.
Arginine vasopressin (AVP) is another neuropeptide and hormone with peripheral effects such as reabsorption of water from tubular fluid and artery constriction. However, in the brain, this neuropeptide plays a role in pair bonding and ‘male’-aggressive behaviours. AVP acts on AVP receptors, V1aR, found in high levels in the ventral pallidum (part of the reward system), medial amydala (fear/fight or flight) and mediodorsal thalamus.
In those well studied, monogamous prairie voles, AVP is vital for pair bond formation in males. In fact, the role of this hormone is so strong that male prairies infused with AVP in the brain form a pair bond with females without mating. If the V1aR AVP receptors are blocked in the ventral pallidum only, the formation of a pair bond during mating is inhibited and when all V1aR receptors are blocked using a drug, male prairie voles cannot recognise their mates. So similar to oxytocin, specific brain regions mediate pair-bond formation in the male brain and this happens to be a region associated with reward. In humans, AVP levels are found to be elevated in men during arousal but it is unclear how these levels distinguish a life-long love from a one-night stand.
Dopamine is a neurotransmitter synthesised in neurons in the ventral tegmental area and substantia nigra. Dopamine is the major neurotransmitter which activates the ‘reward circuit’ in the frontal cortex and its release is associated with goal-directed behaviour, promoting learnt-motivation for certain actions by making you feel gooooode. Dopamine acts at D1 (signal promoting) and D2 (signal blocking) receptors, found in different populations of neurons in the prefrontal cortex. It is thought that activation of prefrontal D1 receptors leads to risky decision making whereas activation of D2 receptors in this region promotes more flexible thinking; considering the reward-risk benefits of an action.
During mating in prairie voles, dopamine systems are activated as these regions contain varying levels of OTR and V1aR, linking copulation and reward sensations. During mating, it has been reported these mammals experience a 51% increase in extracellular dopamine levels and if D2 receptors are activated by drugs, partner preferences are accelerated without the need for mating. In the male prairie vole, the levels of D1 receptors, mediating 'risky' decision making, are actually reduced in the two weeks following mating and pair bond formation; potentially preventing the formation of new pair bond. Even in non-monogamous mammals such as rats, individuals prefer to spend time with partners they have 'done the deed' with over new potential partners due to activation of D2 receptors in the nucleus accumbens when near their previous partner. In humans, fMRI studies on individuals looking at images of their partner vs other faces have revealed dopamine-rich regions are activated by their love interest only. It is thought dopamine acts in tandem with oxytocin or AVP to form a strong, rewarding bond with those you romantically love. In praire voles, bond formation requires D2 activation in the nucleus accumbens in both sexes with concurrent activation of OTR in the nucleus accumbens and prefronatal areas in females and V1aR in the ventral palladum in males. These signals occur alongside olfactory cortex (smell detection) activatino in order to link the hedonic properties of mating to one specific individual.
Can we make a fully-functioning love potion?
So, what would happen if you mixed oxytocin, AVP and dopamine and gave it to your love interest? Would they automatically fall head over heels for you? Well, like all neuroscience, it would most probably be a bit more complicated than that. All of these neuropeptides have receptors across many different brain regions and are responsible for different functions, not just playing cupid. It is also very likely that the timing of the release of these hormones in specific brain regions is vital for catching the love bug. For example, the hypothalamus is reportedly activated in sexual arousal and romantic love but not maternal love. And undoubtedly, there will be many other specific interactions and chemicals involved (I feel you, adrenaline). So much more research needs to be done on the human elements of love in many types of relationships (not just the love between men and women) for us to pin down a more solid mechanism for our monogamous desires. As for the potency of liquid trust? Well, while a squirt of oxytocin up your nose may dampen your suspicions of someone for a few hours, this will soon wear off and you will probably be super freaked out somebody has tried to chemically win you round. While it seems that we might understand some of the key ingredients for the most powerful love potion of all time, the secret recipe of how to mix these ingredients remains locked up inside your brain. And I don’t think it will be release on BBC good food anytime soon.
Happy Palentines everyone! All the info for this article was gathered from the following sources:
Love: Neuroscience reveals all.
The Neurobiology of Pair Bonding
Prefrontal Dopamine D1 and D2 Receptors Regulate Dissociable Aspects of Decision Making via Distinct Ventral Striatal and Amygdalar Circuits