Some muscles controlling facial expressions are not common to everyone

Jun 16 2008

Laugh and the world laughs with you, but wrinkle your nose and you could find yourself on your own. A new study by a scientist at the University of Portsmouth who examined the facial muscles in cadavers, has revealed that the muscles which control our facial expressions are not common to everyone.

The Risorius muscle, which experts believe controls our ability to create an expression of extreme fear, is found in only two thirds of the population.

Dr Bridget Waller has published a study in the American Psychological Association Journal which describes the unique variation of musculature structure in the face.

It is the first systematic study into the variations of muscles in the human face and how this relates to facial expression. It has important implications for our understanding of non-verbal communication.

Dr Waller is from the Centre for the Study of Emotion in the Department of Psychology. She collaborated with anatomists at the University of Pittsburgh and Duquesne University in the USA.

They found that all humans have a core set of five facial muscles which they believe control our ability to produce a set of standard expressions which convey anger, happiness, surprise, fear, sadness and disgust. But there are up to nineteen muscles which may be present in the face and many people do not possess all of them.

Dr Waller said: "Everyone communicates using a set of common signals and so we would expect to find that the muscles do not vary among individuals. The results are surprising - in some individuals we found only 60 per cent of the available muscles."

She said that everyone is able to produce the same basic facial expressions and movements but we also have individual variations.

"Some less common facial expressions may be unique to certain people," she said. "The ability to produce subtly different variants of facial expressions may allow us to develop individual 'signatures' that are specific to certain individuals."

She said that there are significant implications for the importance of facial expression in society.

"Facial expression serves an essential function in society and may be a form of social bonding," Dr Waller said. "It allows us to synchronise our behaviour and understand each other better."

Dr Waller has completed studies which examined facial expressions in apes. She said that primates who live within social groups have a more elaborate communication repertoire including more complex facial expressions.

"There is a theory that language evolved to help us bond us together in social groups and we may be able to apply the same theory to facial expressions," she said.

The face is the only part of the human anatomy which has been found to display such a massive variation in muscle structure. In the only other example of muscular differences, the forearm has a muscle which approximately fifteen per cent of the population don't have.

Dr Anne Burrows from Duquesne University was one of the anatomists on the study. She said: "The problems with quantifying facial musculature is that they're not like other muscles. They're fairly flat, difficult to separate from surrounding connective tissue and they all attach to one another. They are very unlike muscles of the limbs, for example.

"The variation we see in the face is absolutely unique," said Dr Waller.

Dr Waller said that actors need not worry because people will compensate for a lack of one muscle by using another to develop a similar expression. And people can learn to develop a facial expression by practising in front of a mirror.

"As humans we are able to change the level of control we have over our facial expressions," said Dr Waller. "There is a great deal of asymmetry in the face and the left side is generally more expressive than the right. But someone who is unable to raise one eyebrow without raising the other could in fact learn to raise just one."

The implication for those actors who have had botox speaks for itself.