Love: A Cocktail of Chemicals

By Nick Bitterlich

Love is a sensation most people have experienced in one form or another; be it from loving a significant other, one’s parents, or a best friend. An array of feelings is associated with love, commonly including exhilaration, euphoria, a racing heart, anxiety, or “butterflies”. Scientists have been questioning the nature of the process for decades, having reached no precise answer to this day. What does go on behind the scenes is a fascinating interplay of hormonal reactions: a cocktail of chemicals. 

Love comes in a number of forms, including but not limited to lust, attraction and attachment, all of which have different chemical profiles. Nevertheless, the primary neurochemicals (neurotransmitters, sex hormones and neuropeptides) that govern the processes mentioned above are testosterone, oestrogen, dopamine, vasopressin and oxytocin (Fisher, Aron & Brown, 2006): 

Dopamine pathways define our partner preference whereas vasopressin and oxytocin mediate our attachment behaviours via the ventral pallidum and nucleus accumbens respectively. Sex drive is controlled by the behaviour of the mesolimbic dopamine pathway and is heavily dependent on testosterone and oestrogen, both of which modulate its activity (Fisher, Aron & Brown, 2006). Threshold concentrations of testosterone appear to be required as a sexual driving force in both males and females via the release of dopamine and oxytocin. In fact, chemicals triggered during passionate love seem to depend more on the activity both partners participate in rather than the people involved themselves (Seshadri, 2016).  

One chemical frequently associated with the process is dopamine, the brain’s reward pathway produced in the hypothalamus. High levels of dopamine and a related hormone, norepinephrine, are released during attraction and sexual acts, hence the energetic and euphoric sensation many experience (Wu, 2019). A common side effect of the hormone is insomnia, implying an individual can be “in love” to an extent where it prevents them from sleeping. An explanation for this may be the presence of norepinephrine, also known as noradrenaline, which plays a role in the fight and flight response, keeping us alert (Klein, 2013). 

Another hormone often associated with love is neuropeptide oxytocin. In mammals it is crucial in helping expel babies from the uterus and creating lasting bond between mother and offspring. While new-borns depend on their mother’s milk, mammal mothers form strong and lasting bonds with their new-borns immediately after birth to sustain the survival of the baby (Carter & Porges, 2013). Nevertheless, women who give birth via a caesarean section, fathers, grandparents and adoptive parents also form lifelong attachments to children. Some evidence suggests that the presence of an infant releases oxytocin in adults, “persuading” its caretakers to love it. Oxytocin therefore might help to assure that parents and others will engage with and care for infants, to stabilize loving relationships (Carter & Porges, 2013).

To decipher the nature of love, techniques such as fMRI brain scanning, including magnetic resonance imaging, show the regions of the brain activated when someone feels ‘love’. Brain scans of people “in love” indicated an influx of activity within the primary reward centres of the brain including the ventral tegmental area and the caudate nucleus. A 2000 study by Bartles and Zeki (2000) discovered the activation of two particular regions: the foci in the media insula and the anterior cingulate cortex. Conventionally these sections of the brain were associated with instinct and euphoria, suggesting an evolutionary history to the feeling of love. In fact, the evolutionary pathways that led from reptiles to mammals allowed the emergence of the unique anatomical systems and biochemical mechanisms that enable social engagement, and hence feelings such has love. These reciprocal interactions trigger dynamic feedback mechanisms that foster growth and health. Furthermore, a study conducted by Ortigue et al. (2007) suggested triggering memories of a partner triggered emotion and motivational brain regions, including the caudate nucleus, bilateral fusiform regions and bilateral angular gyri, which is associated with integrating abstract representations, hence feelings and potentially love.  

Despite the pleasure centres activated by love, a ‘broken heart’ or a failed relationship can have disastrous effects that may disrupt human physiology and might even cause death. The behaviours and strong emotions triggered by love might leave us vulnerable and its withdrawal effects are often just as severe as those experienced by a drug addict. It’s important to note that heartbreak falls under “social pain”—the activation of pain in response to the loss of or threats to social connection. Dopamine, for instance, surges in a similar manner during love than a drug addict taking cocaine (Wu, 2019). Cocaine maintains dopamine signalling longer than normal, creating a prolonged “high”. In a way, the attraction we experience is much like an addiction to another human being. Addicts going into withdrawal are thus not unlike love-struck people craving the company of someone they cannot see.

Oxytocin follows the same principle of too much is harmful; studies on drugs MDMA and GHB shows that oxytocin may be the hormone behind the “feel-good high” these chemicals produce (McGregor, Callaghan & Hunt, 2008). Furthermore, oxytocin’s role as a “bonding” hormone appears to help reinforce the positive feelings we already feel towards the people we love. As we become more attached to our families, friends, and significant others, oxytocin is working in the background, reminding us why we like these people and increasing our affection for them. Oxytocin has also been suggested to play a role in ethnocentrism, increasing our love for people in our already-established cultural groups and making those unlike us seem more foreign (Carter & Porges, 2013). On the other hand, oxytocin, having anti-inflammatory and antioxidant properties in vitro models of atherosclerosis, can facilitate adult neurogenesis and tissue repair following stressful experiences (McGregor, Callaghan & Hunt, 2008). The heart seems to rely on oxytocin as part of a normal process of protection and self-healing, thus making it a double-edged sword.

Love is not just an emotion; it is a complex combination of biological processes and chemicals that engage with one another in a dynamic manner. Social interactions between individuals trigger cognitive and physiological processes that influence emotional and mental states.  However, there is no precise formula for love. Instead, its composition remains a mystery with many of its questions unanswered. It can bring individuals to their highest, happiest phase while also capable of bringing out the worst. Love is something incapable of being defined by science; everyone’s experience will vary. For better or for worse, if love is solely based on chemical reactions within our body, maybe we can have “chemistry” with just about anybody. 

References:

Bartels, A. and Zeki, S. (2000). The neural basis of romantic love. NeuroReport, [online] 11(17), pp.3829–3834. Available at: https://journals.lww.com/neuroreport/Fulltext/2000/11270/The_neural_basis_of_romantic_love.46.aspx.

Carter, C.S. and Porges, S.W. (2013). The biochemistry of love: an oxytocin hypothesis. EMBO Reports, [online] 14(1), pp.12–16. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3537144/.

Fisher, H.E., Aron, A. and Brown, L.L. (2006). Romantic love: a mammalian brain system for mate choice. Philosophical Transactions of the Royal Society B: Biological Sciences, 361(1476), pp.2173–2186.

Klein, S. (2013). The 3 Major Stress Hormones, Explained. [online] HuffPost. Available at: https://www.huffpost.com/entry/adrenaline-cortisol-stress-hormones_n_3112800.

McGregor, Callaghan and Hunt (2008). From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use? British Journal of Pharmacology, 154(2), pp.358–368.

Ortigue, S., Bianchi-Demicheli, F., Hamilton, A.F. de C. and Grafton, S.T. (2007). The neural basis of love as a subliminal prime: an event-related functional magnetic resonance imaging study. Journal of Cognitive Neuroscience, [online] 19(7), pp.1218–1230. Available at: https://www.ncbi.nlm.nih.gov/pubmed/17583996 [Accessed 20 Apr. 2020].

Seshadri, K.G. (2016). The neuroendocrinology of love. Indian Journal of Endocrinology and Metabolism, [online] 20(4), pp.558–563. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4911849/.

Wu, K. (2019). Science in the News. [online] Science in the News. Available at: http://sitn.hms.harvard.edu/flash/2017/love-actually-science-behind-lust-attraction-companionship/.

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