Feb. 26, 2009 -- Disgust over an unfair or immoral social situation is hard-wired into the human body as strongly as the reaction to a foul taste, according to research published today in the journal Science.
By studying the electrical activity of a muscle in the upper lip in both physically and morally offensive situations, scientists determined that disgust is equally strong in both cases.
"People use the term disgust in terms of morally offensive situations," said Adam Anderson, a professor of neuroscience at the University of Toronto and a co-author on the study. "Our study looked at whether this reaction was genuine disgust or just a metaphor."
At its most basic level, disgust is a physiologic response that keeps a person safe by compelling him or her to spit out contaminated material. Over time, the same response has been adapted to various social situations to offer non-verbal cues that a particular situation is also somehow wrong or unclean.
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The new report is the culmination of four studies spanning several years and involving 80 undergraduates from the University of Toronto.
The first two studies measured students' muscle activity in response to typically physically "disgusting" things: a solution of bitter quinine and images of poop and dirty toilets.
In the next two studies, students played the Ultimatum Game. Simplified, a computer presents a player with many ways to split $10, from fairly (50/50) to unfairly (90/10).
In all four studies scientists stuck electrodes onto the levator labii superioris alaeque nasi, the muscle that curls the upper lip and wrinkles the nose in disgust, to measure electrical activity. The more electrical activity, the greater the lip curl, an indication of greater disgust.
When the Canadian scientists compared the amount of disgust between the first two studies of physical disgust with disgust at immoral or unfair situations, they were able to predict whether a person would accept a particular offer from the computer.
For both sexes the most active region was the parietal lobe that deals with visual perception, spatial orientation and information processing, but it was focused on the right side of the brain in men while both sides participated in women.
While there are differences between people as to what is beautiful and what isn't, Cela-Conde said they did not find identifiable differences related to sex.
"Any person can find beautiful a landscape, a building or a canvas that some others will find awful. But sex has little to do with those differences. Perhaps they relate with other variables, such as age or education." he said.
"It is curious that, using different neural networks, the final result is very similar in women and men. But this seems to be the case," Cela-Conde said.
He added: "Human nature is complex and difficult to study and understand. Nevertheless, thanks to scientific tools we are starting to know a bit more about some very important aspects of our nature."
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