Making Faces

Primate facial expressions may not be solely reflexive

- Cody Cottier

FACIAL EXPRESSIONS ARE CENTRAL to social life, yet scientists still don’t fully understand how the brain produces them. For decades one influential theory has held that what appears on a person's face is largely an emotional reflex—an honest, automatic readout of what they feel inside. But that view doesn’t explain the fact that we often tailor our countenance to the moment: we've all smiled politely through a dull date or tried not to smile while holding a royal flush.

To find out what’s going on in the brain as facial expressions arise, researchers turned to rhesus macaques, Old World monkeys with face musculature and neuroanatomy that are similar to that of humans. They recorded neural activity in the laboratory while the animals interacted with one another, with human experimenters, with digital avatars and with video of other macaques. The team’s results, published recently in