In case you aren’t familiar with this term, 'the Knowledge' is the map of London streets that every local taxi driver must memorize. If you live in a planned community, this might not seem so daunting. However, if you’re a London taxi driver, you must deliver your customers through streets that have been cobbled together, in some cases literally, over the past two millennia. The result is a mass of information that takes three or four years to master, if you’re in the 50% of trainees who make it that far.
What does this have to do with brains? A lot. London cabbies, who by definition have passed a test on the Knowledge, have larger posterior hippocampuses than the rest of us mere mortals. To test whether this intensive learning actually altered people’s brains (perhaps successful London cab drivers simply have larger hippocampuses to begin with), Katherine Woollett and Eleanor Maguire of University College London got their hands on a group of 79 would-be taxi drivers and 31 controls.
All participants were given brain scans and memory tests both at the start of the Knowledge training and four years later. By then, 39 of the trainees had passed their tests and become cab drivers. Before training, there was no difference between the three groups (fully trained, partially trained and not trained). After training, only those people who had fully acquired the Knowledge and qualified as taxi drivers had larger posterior hippocampuses.
Interestingly, the qualified taxi drivers performed worse at other types of memory tasks, such as recalling complex visual information, than either the disqualified trainees or the controls.
By the way, if you think the Knowledge is soon to be replaced by satellite navigation (GPS systems), here's a dissenting view:
For more on this story, check out Ed Yong's blog, Not Exactly Rocket Science.