Cab drivers' grey matter enlarges and adapts to help them store a detailed mental map of the city, according to research.

Taxi drivers given brain scans by scientists at University College London had a larger hippocampus compared with other people. This is a part of the brain associated with navigation in birds and animals.

The scientists also found part of the hippocampus grew larger as the taxi drivers spent more time in the job.

"There seems to be a definite relationship between the navigating they do as a taxi driver and the brain changes," said Dr Eleanor Maguire, who led the research team.

She said: "The hippocampus has changed its structure to accommodate their huge amount of navigating experience."

http://news.bbc.co.uk/1/hi/sci/tech/677048.stm