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Scientists are getting a glimpse of how jokes are processed by the human brain.

Brain scans show that puns and other types of joke are deciphered in different regions.

But to actually appreciate a joke, and have a good laugh, requires the use of a central pathway in the brain.

The finding could explain why some people lose their sense of humour following damage to a particular part of the brain.

To investigate the biology of humour, researchers based at York University in Toronto, Canada, and the Institute of Neurology in London, UK, carried out brain scans on 14 volunteers while their subjects listened to jokes.

'Funniness' scale

They chose two types of joke: so-called semantic jokes, such as "What do engineers use for birth control?...Their personalities" and puns like "Why did the golfer wear two sets of pants?...He got a hole in one".

Laughing was discouraged while scanning was in progress but afterwards each volunteer rated the jokes on a funniness scale of one to five.

Separate regions of the brain process different jokes

Areas of the brain known to be involved in the processing of language were active while the subjects processed semantic jokes.

Different areas of the brain, involved in speech production, lit up when the subjects deciphered puns.

But for both types of jokes, the authors found activation in an area of the brain called the medial prefrontal cortex, which controls reward-related behaviour.

Furthermore, activation in this region correlated with the subjects' funniness ratings.

The authors conclude that separate systems in the brain process different types of jokes. But the pleasure associated with "getting" a joke involves shared circuitry, they say.

The research, published on Sunday in the journal Nature Neuroscience, throws light on the biological nature of humour, and could explain why some types of brain damage affect humour appreciation.

Humour has a complex role in thought, communication and social interactions, and it may be unique to humans.