It isn't easy being a London taxi driver. But does it change your brain? As well as avoiding pedestrians and dodging double-decker buses, London cabbies must pass a rigorous test called the Knowledge, for which they have to memorize the layout of all 25,000 higgledy-piggledy streets within a six-mile radius of Charing Cross, in the centre of the city.

Cabbies' swelling brains Learn more about the latest results as Kerri jumps in a cab with Eleanor Maguire for a chat about the research. You may need a more recent browser or to install the latest version of the Adobe Flash Plugin.

Eleanor Maguire and Katherine Woollett, neuroscientists at University College London, wanted to know whether all this learning changes the part of the brain that deals with memory, called the hippocampus.

In a previous brain-scanning study, Maguire and her team had showed that cabbies have larger hippocampi than non-taxi drivers1. But they tested the drivers at only one point in time. It still wasn’t clear whether the training boosted the hippocampus size, or whether people with larger-than-normal hippocampi might just be more likely to become cabbies.

To investigate further, Maguire and Woollett scanned the brains of novice cab drivers before, during and after their training, and compared the scans with the drivers' success on the Knowledge2. There was no difference in hippocampus size before the training started. But after training, those that passed the test had bigger hippocampi.