By The Economist
http://www.economist.com/node/18864354

“HELL is a city much like London,” opined Percy Bysshe Shelley in 1819. Modern academics agree. Last year Dutch researchers showed that city dwellers have a 21% higher risk of developing anxiety disorders than do their calmer rural countrymen, and a 39% higher risk of developing mood disorders. But exactly how the inner workings of the urban and rural minds cause this difference has remained obscure—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 (fMRI) to examine the brains of city dwellers and country bumpkins 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 doomed to fail (the researchers had designed success rates to be just 25-40%). To make the experience still more humiliating, the team provided negative feedback through headphones, all the while checking participants for indications of stress, such as high blood pressure.

The urbanites’ general mental health did not differ from that of their provincial counterparts. However, their brains dealt with the stress imposed by the experimenters in different ways. These differences were noticeable in two regions: the amygdalas and the perigenual anterior cingulate cortex (pACC). The amygdalas are a pair of structures, one in each cerebral hemisphere, that are found deep inside the brain and are responsible for assessing threats and generating the emotion of fear. The pACC is part of the cerebral cortex (again, found in both hemispheres) that regulates the amygdalas.

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. Not that surprising, to those of a Shelleyesque disposition. 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 whereas 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 correlated with changes in the amygdalas, because of its role in regulating them. fMRI allows such correlations to be measured.

In the cases of those brought up in the countryside, regardless of where they now live, the correlations were as expected. For those brought up in cities, however, these correlations broke down. The regulatory mechanism of the native urbanite, in other words, seems to be out of kilter. Further evidence, then, for Shelley’s point of view. Moreover, it is also known that the pACC-amygdala link is often out of kilter in schizophrenia, and that schizophrenia is more common among city dwellers than country folk. Dr Meyer-Lindenberg is careful not to claim that his results show the cause of this connection. But they might.

Dr Meyer-Lindenberg and his team conducted several subsequent experiments to check their findings. They asked participants to complete more maths tests—and also tests in which they mentally rotated an object—while investigators chided 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 exertion.

As is usually the case in studies of this sort, the sample size was small (and therefore not as robust as might be desirable) 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.