London cab drivers' brains physically grew to hold 'The Knowledge'

Neuroscientist Eleanor Maguire scanned London taxi drivers who had spent years memorising the city's 25,000 streets and found their posterior hippocampus, a brain region tied to spatial memory, was measurably larger than in non-drivers. The longer someone had driven a cab, the bigger that part of their brain was.

— Eleanor Maguire et al., Navigation-Related Structural Change in the Hippocampi of Taxi Drivers — Proceedings of the National Academy of Sciences, 2000