Researchers have discovered that two areas of the brain are directly affected by city living, leading to a greater risk of anxiety and mood disorders.
It was already known that city living is associated with poorer mental health - but not how or why. The new study provides some clues.
"The risk for anxiety disorders is 21 percent higher for people from the city, who also have a 39 percent increase for mood disorders," says co-author Jens Pruessner, a researcher at McGill's Douglas Mental Health University Institute in Montreal.
"In addition, the incidence for schizophrenia is almost doubled for individuals who are born and brought up in cities. These values are a cause for concern and determining the biology behind this is the first step to remedy the trend."
The team looked at the brain activity of healthy volunteers from urban and rural areas. In a series of functional magnetic resonance (fMRI) experiments, they showed that city living was associated with greater stress responses in the amygdala, an area of the brain involved with emotional regulation and mood.
An urban upbringing was also found to be associated with activity in the cingulate cortex, a region involved in regulation of negative affect and stress.
"These findings suggest that different brain regions are sensitive to the experience of city living during different times across the lifespan," says Pruessner.
"Future studies need to clarify the link between psychopathology and these affects in individuals with mental disorders."
Interestingly, it didn't seem to make much difference whether individuals lived in a concrete jungle or a city with a lot of green space. The implication is that it's population density, rather than any other factor, which causes the changes in the brain.
Almost 70 percent of the world population is epxected to live in a city by 2050, according to United Nations projections.