Translated by Rumia Bose
This post is a revised version of “Oxytocine en Lego Technic” published on 22-6-2017.
Oxytocin makes you happy. Or so you read in newspaper headlines and websites. When you cuddle a baby, oxytocin is produced. Oxytocin induces trust. Oxytocin is good for improving social interactions. Oxytocin plays a central role in maternal attachment, friendships and romantic interactions, as it does with sexuality. Oxytocin the cuddle hormone, oxytocin the love hormone. Oxytocin makes for monogamy. And it works for autism, anxiety disorders and schizophrenia by enhancing social interactions.
How does oxytocin work?
Impressive, but too good to be true. How does oxytocin work? Oxytocin is present in all vertebrates and plays a role in reproduction and mating. The oxytocin neurons in the hypothalamus that are responsible for this are also present in humans. These neurons allow release of oxytocin into the bloodstream. That brings about its actions such as uterine contractions after delivery and the let-down reflex which releases milk for breastfeeding. Oxytocin from these same neurons is released into the cerebrospinal fluid which bathes the brain and is stored in cavities (ventricles) within the brain. This influences mating behaviour. It plays the same role in primitive vertebrates with very small brains, such as fish and amphibians.
In the course of evolution other neurons developed in mammals; most extensively in humans. These neurons also originate in the hypothalamus and have dendrites extending to various parts of the brain. Examples are the amygdala which plays an important role in emotions, and the frontal cortex which has an important role in social behaviour. Therefore, oxytocin has a role in mating behaviour in humans similar to that behaviour in lower vertebrates, but in addition it has a role in much more complex behaviour than that seen in lower vertebrates. Complex behavior involves hundreds of substances and scores of brain areas. This is why you can never link complex behaviour to one single substance. Each substance associated with such behaviour plays only a small role in bringing about the behaviour. Otherwise stated: complex behaviour can only be explained by the elaborate interaction of hundreds of chemicals
This means that one particular hormone cannot give rise to cuddling, bring about love, happiness or maternal attachment or social interactions. If this were true, it would be heaven on earth: we would only need to find a way to stimulate oxytocin production in the whole population and that would be it! How then do these wonderful properties of oxytocin make it to the news? You would expect that scientists had found evidence for all of this. Well, scientists have shown that oxytocin does play a small role in bringing about these processes – under certain circumstances. I will use a metaphor to show what this means.
Oxytocin is an ” eight”
My grandchildren play with Lego Technic (as does my 40-year old son). Imagine a Lego car with an advanced steering system. Apart from all sorts of complicated blocks this system contains the classic, simple bricks with 8 knobs, let us call them the “eights”. If you remove the “eights”, then the car does not steer very well. So the “eights” are the steering blocks! The driver’s seat in the car stands on four Lego blocks, of which one is an “eight”. If you remove the “eight” then the seat sags and is crooked, and the driver cannot sit comfortably. So the eight is the seating block! Are the eights now steering blocks or seating blocks? Everyone can see that this is a ridiculous supposition.
Calling oxytocin the love hormone is just as ridiculous. Because a hormone is a molecule, and it functions in the human body just as an “eight” does in a Lego car. It is a necessary component in various functions, but is not THE component for carrying out that function.
Even though the role of oxytocin in a certain behaviour is small, would it perhaps still be possible to influence this behaviour by administering oxytocin? Could we make people happier, less aggressive, more social? Oxytocin can indeed reduce aggression towards others. But it turns out that while this holds true regarding people who belong to the same social group, it does not apply for those outside this group. On the contrary, it seems to increase aggression against people not belonging to one’s own social group. So the effect of oxytocin depends on external circumstances.
Oxytocin has also been extensively investigated for use in people with autism, anxiety disorders and schizophrenia. Sometimes an effect has been found, but such effects are too small to be of practical relevance. What’s more, almost all of these studies have been replicated without finding any positive result. That is not difficult to explain, because oxytocin is delivered using a nasal spray. It is doubtful whether enough oxytocin can enter the brain that way. It certainly does not access the brain areas which control complex behaviour, such as the amygdala or frontal cortex.
Oxytocin in autism?
So are we better off forgetting about treatment with oxytocin? No, I do not want to imply that. It is quite possible that oxytocin plays a role, for instance in autism, and that accurate and detailed research will demonstrate that in some cases tweaking oxytocin at some moments works beneficially. To continue with the metaphor: you first need to know the exact position of the wrongly placed Lego “eight”, and how you can set it just right at precisely the right place. And we are still a long way away from this point, as far as oxytocin and autism are concerned, even if we do get there at all.
Claims in advertisements
The moral of the story is: one molecule in our body is never solely responsible for complex behaviour. This is true not only for oxytocin, but for all molecules. Advertisements often propagate the alleged health benefits of one particular chemical – a food supplement, a hormone, a vitamin. That one chemical can never help for your health problem, unless you just happen to have an isolated deficiency of that specific substance in your body. But in that case you should get yourself checked by a doctor first, because in that case we are talking about a specific and rare medical condition.
Jirikowski GF (2019): Diversity of central oxytocinergic projectionsCell Tissue Res 375:41–48.
Hurlemann R, Grinevich V (eds.) (2018): Behavioral Pharmacology of Neuropeptides: Oxytocin. Springer International Publishing. ISBN 978-3-319-63739-6
Chini B, Verhage M, Grinevich V (2017): The Action Radius of Oxytocin Release in the Mammalian CNS: From Single Vesicles to Behavior. Trends in Pharmacological Sciences 38:982–991.
Grinevich V, Knobloch-Bollmann HS, Eliava M, Busnelli M, Chini B (2016): Assembling the Puzzle: Pathways of Oxytocin Signaling in the Brain. Biological Psychiatry 79:155–164.
Lane A, Luminet O, Nave G, Mikolajczak M (2016): Is there a Publication Bias in Behavioural Intranasal Oxytocin Research on Humans? Opening the File Drawer of One Laboratory. Journal of Neuroendocrinology 28. DOI: 10.1111/jne.12384.
Guastella AJ, Hickie IB (2016): Oxytocin Treatment, Circuitry, and Autism: A Critical Review of the Literature Placing Oxytocin Into the Autism Context. Biol Psychiatry 79:234–42.
Shen H (2015): Neuroscience: The hard science of oxytocin. Nature 522:410–2.
Nave G, Camerer C, McCullough M (2015): Does Oxytocin Increase Trust in Humans? A Critical Review of Research. Perspect Psychol Sci 10:772–89.
Knobloch HS, Grinevich V (2014): Evolution of oxytocin pathways in the brain of vertebrates. Front Behav Neurosci 8. DOI: 10.3389/fnbeh.2014.00031
Shalvi S, De Dreu CK (2014): Oxytocin promotes group-serving dishonesty. Proc Natl Acad Sci U S A 111:5503–7.
Quattrocki E, Friston K (2014): Autism, oxytocin and interoception. Neurosci Biobehav Rev 47:410–30.
Guzman YF, Tronson NC, Jovasevic V, Sato K, Guedea AL, Mizukami H, et al. (2013): Fear-enhancing effects of septal oxytocin receptors. Nat Neurosci 16:1185–7.
Ioannidis JPA (2013): Implausible results in human nutrition research. BMJ 347:f6698.
Churchland PS, Winkielman P (2012): Modulating social behavior with oxytocin: how does it work? What does it mean? Horm Behav 61:392–9.