Cricket commentator Jonathan Agnew's description of Ian Botham's freak dismissal, falling over his own stumps – "He couldn't quite get his leg over" – was all it took to send himself and the late Brian Johnston into paroxysms of laughter. Laughter is truly contagious, and now, scientists studying how our brain responds to emotive sounds believe they understand why.

Researchers at UCL (University College London) and Imperial College London have shown that positive sounds such as laughter or a triumphant "woo hoo!" trigger a response in the listener's brain. This response occurs in the area of the brain that is activated when we smile, as though preparing our facial muscles to laugh. The research, funded by the Wellcome Trust, Action Medical Research and the Barnwood House Trust, is published today in the Journal of Neuroscience.

"It seems that it’s absolutely true that 'laugh and the whole world laughs with you'," says Dr Sophie Scott, a Wellcome Trust Senior Research Fellow at the Institute of Cognitive Neuroscience, UCL. "We've known for some time now that when we are talking to someone, we often mirror their behaviour, 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."

The research team played a series sounds to volunteers whilst measuring their brain's response using an fMRI scanner. Some of the sounds were positive, such as laughter or triumph, whilst others were unpleasant, such as screaming or retching. All of the sounds triggered a response in the volunteer's brain in the premotor cortical region, which prepares the muscles in the face to respond accordingly, though the response was greater for positive sounds, suggesting that these were more contagious than negative sounds. The researchers believe this explains why we respond to laughter or cheering with an involuntary smile.

"We usually encounter positive emotions, such as laughter or cheering, in group situations, whether watching a comedy programme with family or a football game with friends," says Dr Scott. "This response in the brain, automatically priming us to smile or laugh, provides a way of mirroring the behaviour of others, something which helps us interact socially. It could play an important role in building strong bonds between individuals in a group."

So, if you want Christmas with the extended family to go swimmingly, maybe you should switch off Eastenders and dig out your Only Fools and Horses DVDs.

From Wellcome Trust