A well-known side effect of Botox is the inability to fully express emotions. Now research reveals another side effect: the inability to fully feel emotions.
Don't miss these Health stories
More women opting for preventive mastectomy - but should they be?
Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.
- Larry Page's damaged vocal cords: Treatment comes with trade-offs
- Report questioning salt guidelines riles heart experts
- CDC: 2012 was deadliest year for West Nile in US
- What stresses moms most? Themselves, survey says
- More women opting for preventive mastectomy - but should they be?
That means no unsightly wrinkles, but also no moving those muscles at all — which could have more significant consequences than simply looking frozen, the researchers found.
Scientists think that facial expressions themselves may influence emotional experiences, so a person with a limited ability to make facial expressions may also have a limited ability to feel emotions.
"With Botox, a person can respond otherwise normally to an emotional event, [such as] a sad movie scene, but will have less movement in the facial muscles that have been injected, and therefore less feedback to the brain about such facial expressivity," said researcher Joshua Davis, a psychologist at Barnard College in New York. "It thus allows for a test of whether facial expressions and the sensory feedback from them to the brain can influence our emotions."
Compared with the control group, the Botox participants "exhibited an overall significant decrease in the strength of emotional experience," the researchers wrote in a paper published in the June issue of the journal Emotion. In particular, the Botox group responded less strongly to mildly positive clips after they had the injections than before the Botox.
The findings tie into an idea suggested more than a century ago that feedback from facial expressions to the brain can influence the experience of emotions, the researchers said. The simple act of smiling, for example, can help make you feel happy, while frowning can bring down your mood.
"In a bigger picture sense, the work fits with common beliefs, such as 'fake it till you make it,'" Davis said.
© 2012 LiveScience.com. All rights reserved.