"When you're smilin'....keep on smilin'
The whole world smiles with you"
-Louis Armstrong

"When You're Smiling" - as tiny infants, we learn the truth behind the lyrics to this great song. With our first smiles, we receive encouraging smiles back from the people around us. But the song lyrics actually tell us something more, something fundamental about the workings of the human brain.

Using brain imaging, scientists have explored the areas of the brain that are activated when we see another person smile. Of course, you'd expect the visual areas of the brain to light up. But other areas of the brain light up too, including the premotor cortex, an area that helps activate our own smiling muscles and the somatosensory and insula cortices, areas that report what it feels like physically and emotionally to smile. Neurons that fire both when we observe and when we take part in an action are called mirror neurons. When we see someone smile, mirror neurons simulate our own smiling. Does this simulation or reenactment help us to understand what another person is feeling?

In 2007, scientists described an experiment in which they asked their subjects to view photographs of other people's faces and evaluate their facial expressions. In some trials, the participants had to bite down hard on a pen while looking at the photos. When biting down hard, the participants could not use their facial muscles to smile. Under these conditions, the participants were much poorer at recognizing happy expressions in the photographs.

Just this month, in the Journal of Neuroscience, scientists reported further evidence of the connection between mental simulation and facial recognition. They used in their experiments participants with "mirror-touch synesthesia." When mirror-touch synesthetes observe another person being touched, they actually feel the touch sensation on their own body. They may possess a more active mirror neuron system than most. If so, the scientists speculated, they may be better at mentally simulating and thus evaluating facial or emotional expressions. Their tests revealed that the mirror-touch synesthetes, though no better than control subjects at identifying individual faces, were indeed superior at recognizing facial expressions.

One of the greatest experts on facial expressions is psychologist Paul Ekman. In the 1980's, while he and his colleagues were studying and thus making faces that signaled sadness and distress, they began to feel terrible. So they monitored their own body changes as they practiced the expressions and discovered that the sad expressions created marked changes in their autonomic nervous system, changes that would have developed if they were truly sad.

When we see another person smile and then mentally simulate that smile or respond with one of our own, we feel happier. A simple view of another person smiling triggers a whole series of changes in our brain and autonomic nervous system. We can never really know what it feels like to be someone else, but our mirror neuron system and ability to mentally simulate another's actions may bring us closer to understanding each other.

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