Brain scans and the mental health of the megalopolitan

Ah, stress and the city... can't you just feel that vibrant neural nuisance pulsing through?

Neuroscientists reveal this week that urban upbringing and city dwelling have neural effects on the way we respond to social stress.

Decades ago, epidemiology studies showed that growing up or living in cities increases the probability of developing mental health issues, such as schizophrenia and anxiety and stress disorders – compared with being raised in the countryside.

If living conditions affect the way certain brain structures process stress, are those of us in urban environments – more than half of the world’s population – at risk for mental disorders?

"Urbanicity… has a much higher associated risk than any gene," says study researcher Andreas Meyer-Lindenberg of the University of Heidelberg. "The idea was to take people with that risk factor and see if there's anything different in their brains."

So, he and his team decided to puzzle out the neural mechanisms that underlie the connection between city living and mental health (and in particular, sensitivity to social stress).

1. To monitor brain activity, the team used functional magnetic resonance imaging (fMRI) to scan the brains of 32 healthy students as they took a math test they were doomed to fail (the researchers had designed success rates to be just 25-40%).
2. Their pressure levels were measured using with heart rates, blood pressure, and stress hormone levels.
3. At the same time, the researchers dished out negative feedback, telling students they were performing below average and making them feel like they were failing. “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,’” Meyer-Lindenberg says.
4. Then as a follow-up, the researchers literally frowned at another 23 volunteers in a similar experiment.

In response to these stresses, the amygdala and cingulate cortex – areas of the brain involved in processing emotions – were more active in students who lived or were brought up in cities.

“We provide the first mechanism that links cities to mental illness via social stress,” Meyer-Lindenberg says.

• The bigger the city they currently live in, the more amygdala activity exhibited during social stress.
• The more time they spent in a city as a child, the more the cingulate cortex races.

In short, Wired reports, city brains had disproportionately amplified responses to social stress... they’d become sensitized.

Although a dozen or so genes have been linked to schizophrenia, "even the most powerful of these genes conveys only a 20% increased risk," Meyer-Lindenberg says. Schizophrenia is twice as common in those who are city-born and raised than in their provincial counterparts.

The risk for anxiety disorders is 21% higher for urbanites, who also have a 39% increase for mood disorders.

Determining the biology behind this is the first step to remedy these trends, says study coauthor Jens Pruessner of McGill University.

The researchers plan to repeat the work in the general population to clarify links between stress processing and the biological impacts of city living, such as being an immigrant, population density, pollution, crowding, housing types, social hierarchies, and green space.

While the work doesn't prove that living in the city causes the changes in the brain, it could be used to help improve life for city dwellers.

The study was published in Nature this week.

Image of 3 categories of living conditions: rural areas, towns with more 10,000+ inhabitants, and cities with 100,000+ inhabitants / from Social neuroscience: Stress and the city

This post was originally published on Smartplanet.com