Donders Wonders

Oxytocin: a real neuro-hype

This post is also available in Dutch.

According to psychological research from the beginning of this century, oxytocin is responsible for love and happiness. Currently, science is a lot more sceptical. How is this possible?

In 2005 a team of Swiss scientists published a famous paper on a simple experiment. The neural hormone oxytocin was administered to their participants via a nasal spray. Subsequently the participants played a ‘Trust Game,’ a type of economic simulation to measure mutual trust. What came out of it? After inhaling the oxytocin, participants trusted each other more!

In the years thereafter psychologist Paul Zak, who contributed to the project, became known as ‘Doctor Love.’ He had done a lot more research about the effects of oxytocin and was convinced that it was the source of friendship and love. His enthusiastic TED talk from 2011 can be seen here:

‘Dr. Love’ Paul Zak in his TED-talk. Source: YouTube.

Of course the media were going crazy over the love hormone. Imagine: just one simple molecule in a nasal spray and love will come your way! It is no surprise that all kinds of businesses emerged where you could order your oxytocin online.

You can probably already see it coming: oxytocin was a hype. By now science is a lot more sceptical about the functionality of the substance. Many oxytocin studies were performed badly, for example by testing it on a small number of people. Also it is questionable how much oxytocin actually reaches the brain when administered via the nose.

As a final blow three leading researchers published an overview study in 2015 in which they concluded that there is no link between oxytocin and mutual trust in humans. The finding from the abovementioned Trust Game had probably been coincidental. The myth had lasted a decennium.

Publication bias
There is probably no link between oxytocin and trust, however there was still this famous study in 2005 that found a connection. How is this possible? A part of the explanation is the phenomenon of ‘publication bias’ in scientific literature.

Scientific journals almost exclusively publish ‘positive’ results, meaning studies that found a connection between two things. Such studies support the existence of a relationship between variable A (for example: administering oxytocin) and variable B (more mutual trust). It could be that twenty other researchers did the exact same study as Zak, but did not find any relationship between oxytocin and trust and therefore never wrote the study out in a paper. Zak’s coincidental finding thus was the only positive result and the only one to make it to publication. This however led to everybody suddenly believing oxytocin benefited trust.

Publication bias and other problems make it so that you should take the content of psychological journals with a grain of salt. But that should actually not be news, especially not for science journalists. Science is continuously updating the knowledge of our world, so it is a bad idea to mindlessly believe scientific results or to present them as indisputable facts.

However, Zaks’ research does not have to be discarded altogether. Although oxytocin might not create a ready-made solution for trust in the Trust Game, the much-discussed substance does play other important social roles in mammals. For example, a few weeks ago the role of oxytocin in social bonding in mice came once again to the attention of the leading scientific journal Science. Nuance is therefore needed in both accepting and rejecting scientific knowledge.

This blog was written by Jeroen. Editor: Annelies. Translation: Rowena.

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