"For the fearful images, there is a lot going on there in the brain," de Gelder said.
The results may help explain how fear spreads.
"If there is any form of contagion that is adaptive, it is the immediate response to the fear of others," said Frans de Waal, a psychology professor at Emory University in Atlanta, Georgia. "If others are fearful, there may be good reason for you to be fearful too."
This fear contagion is easily observed in the animal world.
"If one bird foraging in a flock on the ground suddenly takes off, all other birds will take off immediately after, before they even know what's going on. The one who stays behind may be prey," de Waal said.
The study also shows that the brain's emotional response to fear is probably simpler and more automatic than some researchers have assumed in the past. At a fearful moment, animals and humans need to be response ready, since they are given only a fraction of a second to evaluate the situation.
"Let's say a fire erupts," de Gelder said. "Very quickly [people] will basically adopt the body posture of the person next to them. Evolutionarily, it's a very effective mechanism."
But in higher organisms like humans, that efficiency is sometimes slowed as people start thinking of what they should do.
"They say, Why should I run? Let me look first if there is a reason to run," she said.
De Gelder and her colleagues are now conducting their experiment using full video images, which some scientists say could generate different responses.
"How much more emotional arousal might we see if we were actually in truly fearful situations, as opposed to [being in] the safety of brain scanners?" said Jaak Panksepp, a neuroscientist at Northwestern University in Evanston, Illinois.
Several teams around the world, including de Gelder's, are conducting experiments in which the brain activity of participants is scanned while they're watching movies. This enables scientists to study how emotional actions are based on movement.
In the future such research may help scientists diagnose mental diseases such as Alzheimer's and disorders such as autism and schizophrenia. It may also used in building robotic human companions, which could be improved by building principles of "emotional movement" into them.
Don't Miss a Discovery
Sign up for the free Inside National Geographic newsletter. Every two weeks we'll send you our top news stories by e-mail.
SOURCES AND RELATED WEB SITES