and toddlers will happily play with their faeces they soon discover that they shouldn’t, suggesting that they only learn disgust through social conditioning. This is reinforced by a study which examined fifty children who had grown up in the wild; none showed any signs of disgust at bodily products. However, toddlers tend to learn disgust at faeces particularly easily, leading some such as Val Curtis, who researches hygiene and disgust at the London School of Hygiene and Tropical Medicine, to suggest that we are born with a propensity to find certain objects disgusting; it’s far easier to convince children to be revolted by faeces than by sweets. Having said that, it is impossible to disentangle the influence of socialisation. Inevitably it would be difficult to train a child to believe that sweets are disgusting because other children would soon undermine this view, whereas disgust at faeces is reinforced by every adult or older child they meet.
As children develop, their responses to disgust become more sophisticated. Imagine you go into a room where you’re given a glass of clean, fresh water. You drink some water and then you’re asked to spit into the glass before taking another sip. Would you do it? It is your own saliva after all and only moments before it was in your mouth. Then you’re given a fresh glass of water and a dead, but sterilised, cockroach is held in tweezers and dipped into the water. There’s nothing physically wrong with the drink in either case but when university researchers gave people these tasks most wouldn’t do it. At the age of four children will happily drink up, but by seven, like adults, they don’t want to. Before this age they might not possess the complex thought processes which would allow them to see contamination in the same (admittedly at times irrational) way as adults. An understanding of contamination requires the ability to follow a long chain of events. In order to feel repulsed by the idea of licking an object which has fallen on the floor, you need to consider that somebody who had previously stepped in dog faeces would have a dirty shoe which then touched the floor, thus contaminating the food, and finally you. By the age of seven or eight children’s thinking skills have developed to an extent where they can not only follow this chain, but can use disgust to their advantage with ploys such as licking the last biscuit and then offering it to their squirming sibling with the words, ‘Go on – eat it then!’
the disgusted brain
The fact that the facial expression for disgust is so striking reflects the significance of our ability both to convey disgust and to detect it in others. If one person tastes contaminated food everyone else needs to know to stay away from it. The disgust face is so central to this communication that the brain has a specific mechanism for detecting disgust in others. Mary Phillips and her colleagues at the Institute of Psychiatry in London asked volunteers to lie in a brain scanner while they were shown photographs of people displaying facial expressions of either disgust or fear. Cleverly, Dr Phillips set them the task of deciding whether the photograph was of a man or a woman in order to distract them from focusing on trying to identify the expression. Despite the fact that the emotion expressed was irrelevant to the task, the scan nevertheless demonstrated activity in different parts of the volunteer’s brain depending on whether the person in the photograph looked frightened or disgusted.
Deep inside the brain there’s a walnut-shaped area called the amygdala which has tended to be thought of as the seat of all the emotions but with disgust this proved not to be the case. Instead, two areas of the brain are stimulated by disgust – the basal ganglia and the anterior insula, which are both very old parts of the brain in evolutionary terms. People with Huntingdon’s disease have difficulty recognising expressions of disgust which is logical since Huntingdon’s damages the basal ganglia. Extraordinarily, even carriers of the Huntingdon’s gene who do not yet have symptoms of the disease have a reduced capacity for spotting the expression of disgust.
If you were to take a brain and peel back the temporal lobe or side of the brain and look deep inside, behind the ear, you would find a large pyramid-shaped structure known as the insula, a name derived from the Latin for island. The front of this pyramid or anterior insula is the area which responds when we taste strong flavours like salt. This neural link between disgust and taste is intriguing because it lends weight to the idea that disgust exists to protect us from contaminated food. The fact that disgust is found in such an old part of the brain might explain why it is an emotion which is so hard to overcome even when you know there’s no reason to find something disgusting. Even infants who have been born without functioning cerebral hemispheres show expressions of disgust at bitter tastes. This type of instinctive disgust involves no thinking, reflected in the fact that the insula is not associated with brain regions involved in thought and reasoning. This suggests that our brains are hard-wired for us to learn about disgust.
individual responses to disgust
Although we all experience disgust at some time, the strength of the feeling can vary considerably. When Paul Rozin, a world authority on this emotion, measures sensitivity to disgust he finds at one end of the scale people who would be happy to eat live locusts, while at the other end there are people who are not prepared to blow their nose on a brand new piece of toilet roll due to its association with dirty toilets. Women tend to be at least 10-20% more sensitive to disgust than men and that sensitivity also changes over the lifespan, peaking in the teens and tailing off gradually towards old age. From an evolutionary perspective it has been argued that disgust decreases with fertility because a person no longer needs to keep themselves or their offspring healthy in order to continue the species. However, it could be simpler than that; perhaps we become inured to supposedly disgusting sights through caring for dependants. Moreover, as people reach adulthood they gradually worry less about other people’s perceptions, so you might expect a corresponding reduction in the fear that other people might find you or your behaviour disgusting.
Ultimately, a little variation in our individual sensitivity to disgust doesn’t seem to matter and it’s unclear whether the most sensitive people do succeed in avoiding disease more successfully than others. An extreme excess of feelings of disgust can result in an obsessive-compulsive disorder (OCD) involving strict washing routines and lengthy rituals. A person might wash their hands in a precise order, even cupping water in the hand and splashing it over the taps to avoid recontamination when they turn the taps off. These rituals can become so time-consuming that they are disabling. A person might spend every morning scrubbing the kitchen to ensure that it’s definitely germ-free and, in time, might become unable to leave the house because nowhere else is sufficiently hygienic.
The American movie mogul Howard Hughes became so obsessed with the avoidance of germs that he employed staff whose job it was to keep him from contamination. He devised precise rules such as using at least fifteen tissues to open the cabinet where he kept his hearing aid. Before handing him a spoon his servants had to cover the handle in tissue, seal it with tape and then wrap a second tissue on top. His obsession with dirt ruled his life, eventually leading him to live as a recluse.
While researching the way the brain processes disgust, Mary Phillips wondered whether the people with this particular type of OCD might show differences in brain activity. She scanned the brains of people with and without the disorder whilst they looked at a series of pictures that most people would find disgusting, such as photos of filthy toilets and mutilated bodies. In amongst these she added some photos which only those with washing obsessions would be likely to find repulsive – a plate covered in tomato sauce, an unmade bed. The results were striking. The insula was activated in everyone when they saw the disgusting pictures, but it also lit up in people with OCD when they saw the harmless pictures of domestic untidiness. What we can’t tell from this experiment is which came first. Do the people with OCD have an overactive insula, causing them to feel the same degree of revulsion on seeing a dirty plate that the rest of us might feel when we see a dead animal? Or is it the other way around? Is the person so anxious about dirt that this is reflected in their brain activity? Dr Phillips’ forthcoming study might bring us closer to the answer. She’s planning to study people’s brains before and after treatment for OCD. Once they have recovered, the activity in the insula
