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The ancient tale of the Country Mouse and the Town Mouse was only the first to emphasize rural folk's supposed simplicity when compared with more sophisticated urbanites. However, neuro-scientists announce that, in fact, it is city living that can dull the wits.

The new study led by Dr. Spiers at Nantes University describes how they used a dataset from 4 million people of a computer game, which tests navigating skills by asking players to memorise a map showing the location of checkpoints and then measuring how well players can find them, guided only by their mental map. Dr. Spiers and his colleagues examined the 4 million people from 38 countries, and found that the strongest indicator of a high score was a player's age-older people performed relatively poorly, which agrees with what researchers know about age-related cognitive decline. But the benefit of rural living was strong enough to offset some of that. Data showed that a 70-year-old who grew up in the countryside had the navigational abilities of an average 60-year-old across the dataset.

There is a huge gap between the navigation skills of rural and city people, and the researchers think they know why. Dr. Spiers says that the brain's navigational abilities probably weaken in the less challenging city environment because they are not being used as much. Although cities may appear more elaborate, they also feature more clues to help residents find their way, such as numbered streets. In the countryside, however, one field tends to look much the same as another, so there are fewer external landmarks to help guide the way.

Neuroscientists already know that living and working in more complex environments can influence the function and structure of the brain. Brain scans of London taxi drivers, who have gained an encyclopedic memory of the city's streets, show that they tend to have an enlarged hippocampus-a region of the brain acting as a neural GPS, sensing position and path on an internal map of the environment.

The harmful effect of city living on navigation is probably most serious in people under 16-18, Dr. Spiers says, because their still-developing brains respond and change the most according to external stimuli. And while people who live in cities with young children should not be alarmed, the study does raise some interesting ideas for urban planners: keep their city designs not so simple perhaps. And for everyone else, it might be an idea to turn off maps on the phone.