We all knew that city dwellers are more susceptible to mental disorders than their rural counterparts – a new study has shown that specific brain structures respond differently to social stress, depending on whether you are an urban or countryside dweller, researchers from the University of Heidelberg’s Central Institute of Mental Health, Mannheim, Germany, reported in the journal Nature.

Andreas Meyer-Lindenberg and team used functional brain imaging to demonstrate that the brain structures of city people and rural folk really do respond differently to stress. Stress is a key factor in triggering psychotic disorders.

The authors say their study has taken a major step towards defining how living in the city can affect the biology of the brain in such a way as to potentially impact on society. They add that approximately 1% of adults have schizophrenia.

Sociologist Craig Morgan at the Institute of Psychiatry, London, said:

“There has been a long history of mutual antipathy, particularly in psychiatry. But this is the sort of study that can prove to both sides that they can gain from each others’ insights.”

Meyer-Lindenberg explains that genetic factors do influence schizophrenia risk, but only by up to 20% – people with the most powerful of these genes only have a 20% higher risk of developing schizophrenia compared to other individuals. However, city-dwellers have twice the risk of developing schizophrenia compared to people who live in the country. Meyer-Lindenberg added that the risk grows according to the size of the city – the bigger the city the higher the risk.

Meyer-Lindenberg and team wanted to determine how and why city life is associated with a higher chance of developing a mental illness. 32 volunteers underwent brain scans while at the same time carrying out arithmetic tests. Through earphones the researchers would give them negative feedback, telling them they were not doing well and had to speed things up – the aim was to stress them, give them a feeling that they were failing.

The stress, which the researchers define as “social stress”, activated several areas of the brain. They managed to identify two areas which were specific for those who lived in cities – the amygdala and the cingulate cortex. The amygdala processes our emotions, while the cingulate cortex helps regulate the amygdala and processes negative emotions. Put simply, the amygdala and cingulate cortex responded more strongly in the city dwellers than the rural ones.

This first experiment demonstrated such clear and compelling associations, that the team wondered whether their findings might not be believed by other experts. So they performed a similar experiment on 23 other volunteers – these were able to see the researcher’s frowns – they were also exposed to visual feedback. The same clear associations were observed.

These two experiments were on students, Meyer-Lindenberg explained. The team would like to do another study in the general population – they believe their urban vs. rural differences will be even more marked. He also believes that other risk factors may influence mental illness risk, for example, being an immigrant probably affects the way stress is processed.

Meyer-Lindenberg said:

“We will use tools from social scientists to help us quantify things like perceived discrimination, social support networks, or stigma.”

The authors wrote:

“Our results identify distinct neural mechanisms for an established environmental risk factor, link the urban environment for the first time to social stress processing, suggest that brain regions differ in vulnerability to this risk factor across the lifespan, and indicate that experimental interrogation of epidemiological associations is a promising strategy in social neuroscience.”

“City living and urban upbringing affect neural social stress processing in humans”

Florian Lederbogen, Peter Kirsch, Leila Haddad, Fabian Streit, Heike Tost, Philipp Schuch, Stefan Wüst, Jens C. Pruessner, Marcella Rietschel, Michael Deuschle & Andreas Meyer-Lindenberg

Nature 474, 498-501 (23 June 2011) doi:10.1038/nature10190

Written by Christian Nordqvist