Cache Cab: Taxi Drivers’ Brains Grow to Navigate London’s Streets: Scientific American
Maguire wondered whether London taxi drivers also had larger-than-average hippocampi. To earn their licenses, cab drivers in training spend three to four years driving around the city on mopeds, memorizing a labyrinth of 25,000 streets within a 10-kilometer radius of Charing Cross train station, as well as thousands of tourist attractions and hot spots. “The Knowledge,” as it is called, is unique to London taxi licensing and involves a series of grueling exams that only about 50 percent of hopefuls pass.
In her earliest studies, Maguire discovered that London taxi drivers had more gray matter in their posterior hippocampi than people who were similar in age, education and intelligence, but who did not drive taxis. In other words, taxi drivers had plumper memory centers than their peers. It seemed that the longer someone had been driving a taxi, the larger his hippocampus, as though the brain expanded to accommodate the cognitive demands of navigating London’s streets. But it was also possible that The Knowledge selected for people whose memory centers were larger than average in the first place.
To find out which possibility was more likely, Maguire and her U.C.L. colleague Katherine Woollett decided to follow a group of 79 aspiring taxi drivers for four years to measure the growth of their hippocampi with magnetic resonance imaging (MRI) as they completed The Knowledge. For the sake of comparison, Maguire also measured brain growth in 31 people who did not drive taxis but were of similar age, education and intelligence as the taxi trainees. At the start of the study, all of the participants had more or less the same size hippocampi. Maguire also made sure that the aspiring cabbies and non-taxi drivers performed similarly on tests of working memory and long-term memory.