We smile because we are happy, but do we feel happier when we smile? A spate of recent studies suggests that our emotions are reinforced - perhaps even driven - by their corresponding facial expressions.

No one yet fully knows why our facial expressions influence our emotions. Nevertheless, our faces do seem to communicate our states of mind not only to others but also to ourselves.

More than 150 years ago, Charles Darwin proposed that emotional responses influence our feelings, writing 'The free expression by outward signs of an emotion intensifies it.' The pioneering 19th century psychologist William James went further. He said that if someone does not physically express an emotion, he or she has not felt it at all. Although few scientists today would go this far, there is plenty of evidence that emotions involve more than just the brain. The face, in particular, appears to play a big role, acting as a feedback loop. The theory is that the facial changes involved in smiling have direct effects on certain brain activities associated with happiness.

So the moral is, smile even if you don't feel like it. The results may just surprise you.