Miriam Kunz, postdoctoral student at the Universite de Montreal Faculty of Dentistry, conducted the study on 20 men and 20 women between the ages of 18 and 30.
In the study, she placed a heating device on their leg to provoke the painful stimulus, and then asked the test subjects to push a button when the heat became moderately painful, and meanwhile she filmed their facial expressions.
"Individuals who react to pain with intense facial expressions are in fact feeling more pain if we rely on quantitative verbal measures independent of the painful experience," said Kunz.
However, they were found to have a lower tolerance for pain.
"All test subjects with an intense facial reaction to pain estimated that the sensation was "moderately painful" between 45 and 47 degrees Celsius, while others had a higher threshold," she said.
People possess a non-verbal mode of communication influenced by culture, education, age, sex, etc. This mode relies on innate and universal programming. Thus a blind child knows how to smile, even if he has never seen his mother smile.
"Pain, just like joy, sadness, fear, surprise, anger and disgust automatically activate certain muscle groups that make the expression appear on the face," said Kunz.
The study is published in the November issue of Pain.