Do you get squeamish at the site of blood and guts? Does your stomach turn on seeing rotten food riddled with maggots? Visceral responses to disgusting sights are common, but the secret of how we experience such repulsion has long left scientists scratching their heads. 

However, a new study by Cambridge University researchers reveals the key to disgust is quite literally all about our "gut instinct" – by paying participants to stare at horrendous images, scientists have found that we look away from revolting sights not because of our brains, but because of the changes in our stomach's rhythm. 

And now, thanks to the research and a fairly common anti-nausea drug, they have found how to allow humans to look at disgusting sights for longer. Why would anyone want to do this? 

As Cambridge researcher Edwin Dalmaijer tells CGTN Europe, the discovery could have an important real-world impact for treating people struggling with psychopathologies such as obsessive compulsive disorder (OCD). Beyond the clinic, the findings are already giving us a deep insight into the mysterious power of the body over the brain.

 

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Settling the stomach

The key to the study carried out at Cambridge's MRC Cognition and Brain Sciences Unit was getting people used to disgusting sights through the use of the anti-nausea drug domperidone. 

"One of my co-authors, Camilla North, knew of this brilliant drug that is essentially something that settles your stomach," says Dalmaijer. "The idea is that this specific drug really only works on the gut, it doesn't really work on the brain."

Domperidone works by stabilizing the rhythm of the electrical signals in our stomach muscles. These signals that usually help the stomach contract and expand to ensure food moves through our digestive tracts. However, they become abnormal when we are nauseous, and when the rhythms are heavily disrupted – for example, when we see something particularly disgusting – it can lead to our stomachs quite literally turning. 

 

 

"There are core disgust components," explains Dalmaijer: "They include things like feces, vomit, basically anything that if you encounter it, you probably want to avoid it because these tend to be the things that ... potentially make you ill."

The other prevalent core disgust is what the researcher describes as gore, things like blood and organs that shouldn't be on the outside. As the researcher explains, when see something disgusting, "you won't necessarily feel it, but we can measure it in your stomach."

"We were hoping that, because of that settling of the gut [via the drug], maybe the approach to these disgusting images would also potentially be altered," says Dalmaijer, and that's indeed what the researchers discovered.  

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Testing ad nauseum

The 25 volunteers, aged between 18 and 35, were put into to two groups: one group to take domperidone, the second a placebo. Before administering the tablets, Dalmaijer and his colleagues showed both groups a selection of neutral images – pictures of things including scarves and buttons – alongside ones picked specifically to trigger innate disgust responses. 

As they looked, the researchers tracked their eye movements to see on which image – neutral or disgusting – they lingered. Without encouragement, participants naturally looked away from the unpleasant ones.

Thirty minutes after taking their tablets, the participants were shown the images again. The researchers discovered that initially, taking domperidone had little effect on the time spent looking at a particular image, which Dalmaijer chalks up to the fact people don't really habituate to disgust: "I can show you the same picture of a particularly disgusting image and you'll just try to avoid it and you'll continue to do so, even though you've seen it countless times over and over and over."

And as Tim Dalgleish, also from the MRC Unit explains: "Just using the drug itself isn't enough: overcoming disgust avoidance requires us to be motivated or incentivized." 

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Paid to look

Next, the researchers gave the volunteers an incentive: for every four to eight seconds that they looked at a revolting image, they would get 35 cents – and hear a "kerching!" sound. The volunteers then viewed the images for a final time, but this time with no incentive.

As was to be expected, the dwell time went up dramatically when they were paid to look, but Dalmaijer explains that "paying people to look at poo doesn't actually help them at all." 

Adding: "They look at the disgusting images while you pay them and immediately flip back to normal behavior directly when the payment stops."

However, in the final round – when the volunteers were no longer being incentivized – the team discovered those who had received domperidone spent much longer than the placebo group looking at the disgusting images. 

 

 

Those on the placebo looked at the neutral image around 5.5 seconds longer than the disgusting one, but with domperidone, the difference was only roughly 2.5 seconds.

"We've known for some time that when you see something disgusting, your stomach muscles' electrical signals become dysregulated," said Camilla Nord, Dalmaijer's colleague, "which in some cases causes people to feel sick or their stomach to turn. You're then likely to avoid that thing.

"What we've shown here is that when we steady the stomach's electrical signals, people become less avoidant of a disgusting image after engaging with it. Changes in the stomach's rhythm led to reduced disgust avoidance in our study – and so the stomach's rhythm must be one cause of disgust avoidance in general."

 

 

Disgust as treatment 

While Dalmaijer admits "paying people to look at poo" may seem "inherently silly," he underscores the importance of the findings to treating a wide range of anxiety disorders.

"The clearest example would be obsessive compulsive disorder, he says: "Where in some people, they develop compulsions to do a lot of cleaning and they can be driven by a fear of disgusting things."

Psychopathologies such as arachnophobia (the fear of spiders) and post-traumatic stress disorder (PTSD) can also be similarly rooted in our disgust reflex, he explains: "Sometimes people have really particularly gory experiences and they can leave a really big mark on them and that can form into PTSD.

"To get over that initial traumatic experience that was really rather disgusting, this can potentially also help to chip away at that central disgust that is core to these psychopathologies."

One of the main problems with treating such patients has been the lack of habituation to disgusting sights. "This is one reason why treating pathological disgust by exposure is often unsuccessful," he says. "Our research suggests domperidone may help."

 

 

Moral disgust

The question is whether such treatment would work for more moral understandings of repulsion. "We have all sorts of more fanciful disgusts," says Dalmaijer. "Where you might hear someone say, 'Oh, what an absolutely disgusting idea by the politician to ban immigrants or allow gay marriage.'"

Whether metaphorical disgust actually triggers similar reactions to things like feces and gore is unclear. "In science we try to kind of define our words a bit more narrowly," he says. "But they might." 

He adds: "Specifically things like eating insects, which is really common in some parts of the world and can elicit a disgust-like response in other parts of the world – those things might be a bit more linked to stomach responses."

And with relatively little research on the topic, Dalmaijer says he's dying to delve into the topic further: "That's on the top of the list of stuff that I'm going to do next."

Whatever the outcome, by proving our reactions to unpleasant sights are based in our stomachs, not our brains, the researchers have gone a long way to unpicking the powerful relationship between our body and our behavior. 

"We have this strong tendency of thinking the brain, the mind, this is where all of our things are regulated and the body is just a puppet that listens to the brain," says Dalmaijer. 

"This [study] is a really positive example of how sometimes the state of your body can impact your thinking," he adds. "And that's just a really neat little thing."

Video editor: Terry Wilson