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The phrase ‘making my stomach turn’ has usually been taken as simply metaphorical.
Now, UK scientists have proved that changes in our stomach’s natural muscle rhythms can quite literally prompt us to turn away from disgusting sights.
In experiments, the experts successfully used domperidone, a commonly-prescribed anti-nausea drug, to stabilise the rhythm of the electrical signals in stomach muscles.
This made them less prone to turn away when presented with pictures of faeces – but only after they were sufficiently exposed to the pictures while under the influence of the drug, the experts found.
Researchers at the University of Cambridge reveal that changes in the rhythm of our stomachs prompt us to look away from disgusting images. They showed volunteers either neutral images of clothing or disgusting images – of faeces
Scientists have already known that electrical signals help stomach muscles expand and contract, helping move food through the digestive tract.
But the signals’ rhythms can become abnormal when we are hungry or full of food, feeling nauseous or experiencing a strong pang of revulsion.
When they are strongly disrupted – for example, when we feel strong revulsion towards something – they can cause us to throw up the contents of our stomach.
Disgust has evolved to help us survive, encouraging us to avoid things that might spread disease, but for some disgust can become pathological, affecting mental health and quality of life.
‘We’ve known for some time that when you see something disgusting, your stomach muscles’ electrical signals become dysregulated,’ said study author Dr Camilla Nord at the University of Cambridge.
‘[This] 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.’
For their study, 25 volunteers aged between 18 and 35 were randomly assigned to one of two groups – one that received domperidone and the other that received a placebo.
Before taking their pills, volunteers were shown a series of unpleasant images of faeces along with neutral images, such as a scarf or buttons, while the researchers tracked their eye movements to measure where they or not they were avoiding looking at the image.
Half an hour after taking their tablets, the volunteers were again shown the images while their eye movements were tracked again.
Next, the researchers offered an incentive to the volunteers – for every four to eight seconds that they could look at a disgusting image, they would receive 25p and hear a ‘kaching!’ sound.
The money was a way to encourage people to look at the disgusting images for longer, according to study author Dr Edwin Dalmaijer at the University of Cambridge.
Domperidone, which is also known by the brand name Motilium, stabilises the rhythm of the electrical signals in our stomach muscles
‘People are naturally disinclined to look at disgusting images (which is what we measure), so we needed something that would get them to look anyway,’ Dr Dalmaijer told MailOnline.
‘While people receive money for it, they look at the disgusting images even if they would normally avoid them.
‘It is during this time that, under the influence of domperidone, their body likely starts to notice that the disgusting images maybe aren’t quite so bad.’
Lastly, the volunteers viewed the images again for a final round, but this time with no monetary incentive.
The volunteers were also asked to rate how disgusting they found the images at the start and end of the trial.
Volunteers were shown a series of unpleasant images of faeces along with neutral images, such as a scarf or buttons. Half an hour later, the volunteers were again shown the images while their eye movements were tracked again
Participants were then tested again while they were receiving a monetary reward – and one final time without the reward
The researchers found that initially, taking domperidone made little difference to the time the volunteers spent looking at a particular image.
As was expected among both groups, the dwell time increased dramatically when they were paid to look at the images.
But in the final condition when the volunteers were no longer being incentivised, volunteers who had received domperidone spent significantly longer than the placebo group looking at the disgusting images.
By the end, people in the placebo group looked at the neutral image roughly 5.5 seconds more than they did the disgusting image, but under the influence of domperidone, the difference was only about 2.5 seconds.
‘[We saw] a reduction in disgust avoidance after using money to encourage exposure in the domperidone condition, compared to the placebo condition in which people switched back to their normal disgust avoidance after the monetary incentive,’ Dr Dalmaijer explained.
Domperidone made no difference to how disgusting the volunteers rated the images to be, meanwhile.
But the study presents evidence that the drug reduces avoidance to disgusting stumuli following a long period of exposure, provided they’ve been motivated to look at it.
‘We’ve shown that by calming the rhythms of our stomach muscles using anti-nausea drugs, we can help reduce our instinct to look away from a disgusting image,’ said study author Professor Tim Dalgleish, also at the University of Cambridge.
‘But just using the drug itself isn’t enough – overcoming disgust avoidance requires us to be motivated or incentivised.
‘This could provide us with clues on how we can help people overcome pathological disgust clinically, which occurs in a number of mental health conditions and can be disabling.’
The study has been published in Current Biology.
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