A smile can brighten the day of a complete stranger, but have you ever wondered what made that complete stranger return your smile? New research suggests people tend to mimic smiles directed at them based on their feelings of status and power.

The study, which was led by Evan Carr from the University of California, involved 55 participants that were split into two groups. Participants in group one were instructed to write an essay describing a good event in their life, while subjects in group two wrote about a negative experience.

Researchers instructed volunteers to write an essay as a way to inspire feelings of more or less power. Following their essays, volunteers were attached to monitors as a way to measure electrical stimulation of facial muscles. The monitors measured ygomaticus majo, which controls lip movement related to smiling, and the corrugator supercilii, which controls frowning in the brow. In addition, volunteers were instructed to either observe videos of people considered to have high power or individuals who were considered to have low status.

The study revealed that people who were feeling more powerful were more likely to smile in response to another smile if the individual was considered to be less powerful or lower in status. Conversely, if individuals deemed the person to be more powerful, they did not smile back. People who considered themselves less powerful are more inclined to smile back at anyone.

Carr believes people smile back at others as a way to display their own status. People who withhold smiling at someone they perceived more powerful is a way to avoid showing esteem for the individual. While others who considered themselves less powerful smile back as a way to demonstrate submission.

Additionally, Carr found people frown backed when someone they perceived with power frowns at them no matter how powerful the individual feels.

Carr presented his findings at the Society of Neuroscience conference.