Taxi drivers in London are an elite bunch: The law requires them to memorize thousands of streets and places and know how best to navigate between them at a given time of day. You'd think this mastery of geographic trivia would go to their heads. Now, researchers have found that it does, in a way. A certain part of their brains is shaped differently than in people who don't need such detailed mental maps.
The brain region involved in navigation, the hippocampus, plays a starring role in learning and memory. People with damaged hippocampi can't form new memories, while similarly impaired rats get lost in mazes. In some birds and mammals, the hippocampus grows and shrinks with the seasons, expanding when the animal needs to remember where it stored food or travel long distances.
London's taxi drivers arguably face even more daunting navigational challenges. To earn their license, they have to train for about 2 years and pass a series of difficult exams. A previous study had shown that the hippocampus helps out with this job; when researchers imaged drivers' brain activation using positron emission tomography (PET) while the cabbies figured out routes between spots in the city, the back part of the hippocampus lit up.
This time, a team of researchers led by psychologist Eleanor Maguire of University College London used a different brain imaging technique called magnetic resonance imaging (MRI) to map the shape and size of the hippocampus. They compared the brains of 16 male taxi drivers with those of 50 men from a variety of other occupations. The back of the hippocampus, they report in the 14 March online Early Edition of the Proceedings of the National Academy of Sciences, was significantly larger in cab drivers. Furthermore, its size increased with the number of years spent behind the wheel, suggesting that experience, not some preexisting skill at navigation, was responsible. Maguire suggests that the enlarged rear hippocampus may be the spot where cabbies store their spatial knowledge of the streets of London.
"It's a very tantalizing, exciting finding," says psychologist Bruce McNaughton of the University of Arizona in Tucson. But he says the study doesn't prove that the hippocampus is specialized for storing spatial information. People in other professions with heavy demands on memory, such as doctors, might have equally odd-shaped hippocampi that correlate with their years of experience, says McNaughton.