THURSDAY, Dec. 14 (HealthDay News) -- Laughter is contagious, and U.K. scientists say they've identified how your brain is "infected" by mirth.

Researchers at University College London (UCL) found that hearing laughter and other positive sounds trigger a response in the area of the brain that's activated when we smile.

"It seems that it's absolutely true that 'laugh, and the whole world laughs with you'," Dr. Sophie Scott, of the Institute of Cognitive Neuroscience at UCL, said in a prepared statement.

"We've known for some time now that when we are talking to someone, we often mirror their behavior, copying the words they use and mimicking their gestures. Now we've shown that the same appears to apply to laughter too -- at least at the level of the brain."

For this study, the researchers played a series of sounds to volunteers while using functional MRI to monitor their brain responses. The sounds included positive ones such as laughter or cheering and negative ones such as retching or screaming.

All of the sounds triggered a response in the premotor cortical region, which prepares the facial muscles to respond accordingly. However, the response was greater when the volunteers heard positive sounds, which suggests that they're more contagious than negative sounds.

The study was published Dec. 12 in the Journal of Neuroscience.

"We usually encounter positive emotions, such as laughter or cheering, in group situations, whether watching a comedy program with family or a football game with friends," Scott said.

"This response in the brain, automatically priming us to smile or laugh, provides a way of mirroring the behavior of others, something which helps us interact socially. It could play an important role in building strong bonds between individuals in a group."