“HELL is a city much like London,” said Percy Bysshe Shelley in 1819. Modern academics agree. Last year Dutch researchers showed that city dwellers (居民) have a 21% higher risk of suffering from anxiety disorders than do their calmer rural countrymen, and a 39% higher risk of suffering from mood disorders. But exactly how the inner workings of the urban and rural minds cause this difference has remained unclear—until now. A study just published in Nature by Andreas Meyer-Lindenberg of the University of Heidelberg and his colleagues has used a scanning technique called functional magnetic-resonance imaging (机能性磁共振成像，简称fMRI) to examine the brains of city dwellers and countrymen when they are under stress.

    In Dr Meyer-Lindenberg's first experiment, participants lying with their heads in a scanner took maths tests that they were bound to fail (the researchers had designed success rates to be just 25-40%). To make the experience still more embarrassing, the team provided negative feedback through headphones, all the while checking participants for indications of stress, such as high blood pressure.

    The city people's general mental health did not differ from that of the rural countrymen. However, their brains dealt with the stress caused by the experimenters in different ways. These differences were noticeable in two regions: the amygdalas (杏仁核) and the perigenual anterior cingulate cortex (前扣带皮层，简称pACC).

    People living in the countryside had the lowest levels of activity in their amygdalas. Those living in towns had higher levels. City dwellers had the highest. In the case of the pACC, however, what mattered was not where someone was living now, but where he or she was brought up. The more urban a person's childhood, the more active his pACC, regardless of where he was dwelling at the time of the experiment.

    The amygdalas thus seem to respond to the here-and-now while the pACC is programmed early on, and does not react in the same, flexible way as the amygdalas. Second-to-second changes in its activity might, though, be expected to be connected with changes in the amygdalas, because of its role in regulating them. fMRI allows such connections to be measured.

    In the cases of those brought up in the countryside, regardless of where they now live, the connections were as expected. For those brought up in cities, however, these connections broke down. The regulatory mechanism of the native urbanite, in other words, seems to be out of order.

    Dr Meyer-Lindenberg and his team conducted several more experiments to check their findings. They asked participants to complete more maths tests—and also tests in which they were mentally ups and downs—while investigators scolded them about their performance. The results matched those of the first test. They also studied another group of volunteers, who were given stress-free tasks to complete. These experiments showed no activity in either the amygdalas or the pACC, suggesting that the earlier results were indeed the result of social stress rather than mental effort.

    As is usually the case in studies of this sort, the sample size was small and the result showed an association, rather than a definite, causal relationship. That association is, nevertheless, interesting. Living in cities brings many benefits, but Dr Meyer-Lindenberg's work suggests that Shelley and his fellow Romantics had at least half a point.

Title: Do urban brains behave differently from rural ones?