"For those of us who have grown up in the reassuring embrace of grid-patterned streets that run straight and don’t change names every two blocks, Old World cities like London—recently declared the most confusing city in the world by a 12,500-person Nokia Maps survey—present huge challenges. So pity London’s cabbies. Before getting behind the wheel of a black cab, would-be drivers have to pass a test called the Knowledge, which requires them to memorize some 25,000 streets and thousands of landmarks, a task that takes two to four years.
A cognitive map featuring that level of detail, as you might imagine, requires a fair amount of storage space, and, sure enough, University College London neuroscientist Eleanor Maguire found that the back part of the hippocampus in London taxi drivers is enlarged compared with that of the general population. The longer they’ve been driving, the bigger the gap. Maguire also found, though, that the front part of the hippocampus gets correspondingly smaller. “So there is a price to pay for their expertise,” she says."
(h/t Tim O'Reilly)