Why living in cities raises stress

You lie down with your head in a noisy MRI brain scanner. You agreed to take part in this experiment, and at first the psychologists in charge seemed nice.

They set you confusing maths problems to solve against the clock, and you do your best, but they aren't happy. "Can you please concentrate a little better?" they keep saying. Or: "You are among the worst performing individuals to have been studied in this laboratory." It is a relief when time runs out.

Few would enjoy this, and indeed volunteers who underwent it were monitored to make sure they had a stressful time. Their minor suffering, however, provided data for a major study. The researchers, led by Professor Andreas Meyer-Lindenberg of the Central Institute of Mental Health in Germany, were trying to find out more about how different people handled stress. They discovered that city dwellers' brains, compared with people who live in the countryside, seem not to handle it so well.

While Meyer-Lindenberg stressed out the subjects, he looked at two brain regions: the amygdalas and the perigenual anterior cingulate cortex (pACC). The amygdalas are known to be involved in assessing threats and generating fear, while the pACC helps regulate the amygdalas. In stressed city-dwellers, the amygdalas appeared more active; in people from small towns, less so; in people who lived in the countryside, least of all.

And something even more intriguing was happening in the pACC. Here the important relationship was not with where the subjects lived, but where they grew up. Those with rural childhoods showed the least active pACCs, those with urban ones the most. In the urban group, there seemed not to be the same smooth connection between the behaviour of the two brain regions observed in the others. An erratic link between the pACC and the amygdalas is often seen in those with schizophrenia. And schizophrenic people are much more likely to live in cities.

When the results were published in Nature, in 2011, media hailed the study as proof cities send us mad. Of course it proved no such thing - but it did suggest it. The results offered a tempting glimpse at the kind of urban warping of our minds that some people have linked to city life since Sodom and Gomorrah.