In order to drive a traditional black cab in London drivers have to gain "the knowledge" - an intimate
acquaintance with the myriad of streets in a six-mile radius of Charing Cross.
It can take around three years of hard training, and three-quarters of those who embark on the course drop out,
according to Malcolm Linskey, manager of London taxi school Knowledge Point.
"There are 400 prescribed runs which you can be examined on but in reality, you can be asked to join any two
points," he told BBC News Online.
"Most people learn by visualisation but we do have a few tricks which we teach them, for example 'little apples
grow quickly' gives you the order of the theatres on the north side of Shaftesbury Avenue: Lyric, Apollo, Gielgud,
But 'the knowledge' is definitely worth learning - black cab drivers are self-employed can earn significantly
more than minicab drivers. A black cab fare from Shepherd's Bush to Heathrow might cost £50, compared with £28 for
The hippocampus is at the front of the brain and was examined in Magnetic Resonance Imaging (MRI) scans on 16
The tests found the only area of the taxi drivers' brains that was different from the 50 other "control"
subjects was the left and right hippocampus. You want to go where?: London's toughest taxi routes
Palladium, Soho to Liverpool Street Station: complex one-way system at both ends
Chelsea to Tower Hamlets Town Hall: crosses and recrosses the Thames
Spaniards Road, Hampstead, to Bromley-by-Bow: requires knowledge of 48 streets
Dr Maguire said: "One particular region of the hippocampus, the posterior or back, was bigger in the taxi
"The front of the hippocampus was smaller in the taxi drivers compared to the controls.
"This is very interesting because we now see there can be structural changes in healthy human brains."
The posterior hippocampus was also more developed in taxi drivers who had been in the career for 40 years than
in those who had been driving for a shorter period.
David Cohen from the London Cab Drivers' Club said he was surprised by the findings: "I never noticed part of my
brain growing - it makes you wonder what happened to the rest of it.
"You do have to have a retentive memory but you also need a placid temperament to drive in London traffic," he
The UCL researchers think evidence that the brain is able to change physically according to the way it is used
could have important implications for people with brain damage or diseases such as Parkinson's.