First published 6/22/11 on The Doctor Weighs In
“Everybody knows” that living in the city with overcrowding, high pressure and anxiety-provoking situations is bound to affect you somehow, and not in a good way. But is it a fact? We don’t know. What “everybody knows” is likely to be wrong, and Intuition is no science.
Physicians practicing in inner city settings know from experience that a large proportion of their patients suffer from chronic anxiety and mental illness. But this, too, does not amount to science.
But there are some studies with tantalizing clues. Some of the best-established effects of urbanization concern mental health. Meta-analyses (statistical analysis that combines data from several studies on a given subject) show that current city dwellers have a substantially increased risk for anxiety disorders (by 21%) and mood disorders (by 39%). For the major brain disorder schizophrenia, incidence is about doubled in subjects born and brought up in cities, with evidence of a dose–response relationship that probably reflects causation. Let’s pause for a second and digest this statement. Schizophrenia has been considered to be a product of genetic predisposition and environmental influences. But doubling the risk of having the disease by living in the city says that environmental factors associated with cities have a strong correlation with the disease. Add to that the evidence that the risk increased as the size of the city increased (a dose –response relationship), and the correlation is becoming pretty compelling. Here is another intriguing fact: the effect is most pronounced if a person lived in the city up to age 15, and the influence fades if one moves to the city at an older age. Since the brain develops and shapes itself from birth to puberty, it suggests that the “city factors”, whatever they are, interfere with proper neurodevelopment.
Urban Stress and the Brain
In a remarkable paper in Nature (June 22, 2011), a group of scientists from the University of Heidelberg in Germany asked the question: can urbanicity cause measurable changes in the brain? For that purpose they placed ads in local newspapers to recruit 32 healthy German adults from cities (with more than 100,000 inhabitants), towns (with more than 10,000 inhabitants), or rural areas. Inside a functional magnetic resonance imaging (fMRI) scanner, they had the subject work on difficult arithmetic problems while a fake “performance monitor” indicated a dismal success rate compared with other subjects. Then the researchers ramped up the stress. As Meyer-Lindenberg, the head of the group, explained: “We would call them in between runs and say, ‘We notice this seems to be very hard for you, but please understand these experiments are very expensive, so if you could just try to at least be above the bottom quarter, we’d really appreciate it.’ “Measurements of the subjects’ heart rates, blood pressure, and stress hormone levels indicated that the stress was indeed getting to them. I don’t know about you, but just reading it raised my blood pressure.
And the results: the fMRI scans showed that volunteers who currently lived in a city exhibited greater activation in the amygdala than did rural dwellers. The amygdala, among other roles, evaluates social threats and is overactive in people with anxiety disorders. But here is the surprise: people who’d been raised in a city, regardless of their current home, showed an additional area of activation: in the perigenual anterior cingulate cortex (pACC). This region is thought to be involved in emotion and social processing, and is implicated in some studies on schizophrenia. Meyer-Lindenberg, leader of the group, suggests that the pACC may be susceptible to lasting effects from the environment early in life, whereas the amygdala is more sensitive to one’s current situation.
As far as I know, this is the first study showing a direct effect of urban living on specific areas of the brain. Furthermore, one of those areas, the pACC, is implicated in schizophrenia, which in turn is correlated with urbanicity. Very suggestive, but of course needs further work to nail it down.
Urbanization, a process that started in North America and Western Europe but is now mainly occurring in developing nations, is a major socio-ecological change confronting mankind. By 2050, 69% of humans will live in urban areas. Although city dwellers, on average, are wealthier and receive improved sanitation, nutrition, contraception and health care, urban living is also associated with increased risk for chronic disorders, a more demanding and stressful social environment and greater social disparities. It is therefore imperative that rigorous science, like the present study, be applied to the problem with some urgency
Dov Michaeli MD, PhD is a basic researcher who writes on The Doctor Weighs In.