Have you ever had the experience of smiling to be sociable at a party, even though you don’t feel especially chipper, and finding that the smile actually makes you feel happier? Or of making a frown, perhaps when you’re in a meeting where layoffs are announced (even though your job is safe), to show that you are in sync with others, and even though you did not feel angry before you frowned the facial expression makes you feel mad? The phenomenon was first noticed by Charles Darwin, giving rise to his “facial feedback hypothesis”—but Darwin didn’t know anyone who’d had Botox.
Scientists therefore ran a cool little study in which they compared people before and after they had Botox treatments that immobilized their frown muscles. One mystery that still surrounds the facial-feedback effect is whether the feeling of happiness or anger induced by smiling or frowning is due to the brain activity that causes the muscles to move, or to the actual muscle movement that, presumably, sends feedback to the brain. If only the brain activity sending the command “smile!” or “frown!” matters, then the fact that the immobilized muscles don’t move shouldn’t matter; people should still feel the emotion.
In a paper in the March issue of the journal Cerebral Cortex, scientists led by Andreas Hennenlotter and Bernhard Haslinger of the Tcchnische Universitat Munchen and the Max Planck Institut für Kognitions (Human Cognitive and Brain Sciences), both in Germany, note that when people imitate facial expressions, their brain’s emotion regions become more active. To tease apart whether the actual muscle movement is causing the effect, they studied 38 women who received Botox (botulinum toxin) injections to their frown muscles (to reduce lines in their forehead).
Before Botox, imitating pictures of sad or angry facial expressions caused a large increase in activity in the amygdala, a key emotion region for, especially, anger and anxiety. But after Botox, imitating the angry expressions caused a much lower level of activity in the left amygdala. (The British Psychological Society did a nice write-up of the study here.) This suggests that making an angry face affects the amygdala through feedback from the facial muscles and skin (the latter being absent for the botox-injected women). There was no difference in amygdala activation pre- and post-Botox when the women imitated sad expressions, reinforcing the idea that muscle movement is key to inducing the emotion; their Botox shots did not immobilize muscles that make a sad face.
The scientists conclude that “during imitation of angry facial expressions, reduced feedback due to [Botox] treatment attenuates activation of the left amygdala . . . . These findings demonstrate that facial feedback modulates neural activity within central circuitries of emotion during intentional imitation of facial expressions.” Any thoughts on whether immobilizing the smile muscles takes away the ability to feel happiness when you make yourself smile—or, in the case of Botoxers, try but fail to smile?