I recently moved to a big city from a series of smaller, suburban cities and towns. I love my new city dwelling, the opportunities that are available to see the arts, the large universities and hospitals which allow for scientific collaboration, the cool, fun bars, and of course, the fact that I can get Ethiopian food freakin' DELIVERED at 2am if I should so choose. And most of the time, I love the hustle and bustle, though we often wish to get a little more green in our eyes.

City living is a pretty "new" concept in human history, but it's grown by leaps and bounds. Like me, people have continued to move to cities from the country over the past few thousand years. Right now more than half the world's population lives in cities, and urbanization in developing nations will continue to increase that number. Of course, there are benefits to living in cities, or people wouldn't bother. Benefits like better sanitation, nutrition, health care, etc (in general). But there are downsides to living in cities as well, an increased risk for chronic illness, increased social stress, larger social disparity, a greater divide between the rich and the poor. And now this recent paper asks, what about our mental health?

Lederbogen, et al. "City living and urban upbringing affect neural social stress processing in humans" Nature, 2011.

The fact is that there is a higher concentration of psychiatric illness in the city than in the country. There is increased risk for anxiety disorders, mood disorders, and schizophrenia. Of course, there are lots of possible reasons for this. There is a greater socioeconomic divide in cities, and people of low socio-economic class have a higher risk for psychiatric disease. There is also better access to health care in cities, and someone who might pass as just "very odd" in the country is more likely to get diagnosed in the city. Finally, it is often easier to function in a city with a severe mental illness, with some better access to shelter, care, and emergency medicine.

But there is also some evidence that living in a city can "bring on" mental disorders. While many mental disorders are thought to have a genetic component to some degree, the addition of stress may be able to bring out an underlying mental illness. And of course, cities are stressful. Specifically, cities produce social stress, the stress of living around and being seen (or feeling you're being seen) by lots of people, constantly.

The authors of this study wanted to look at how urban upbringing, and living in an urban environment currently, affected the way people processed social stress. They took a bunch of healthy volunteers, half from the city, and half from the country (pretty small numbers here, but that's usual in these studies). They stuck them in an fMRI and examined their brain activity at baseline and during a social stress test. For the social stress test, they had the participants perform difficult arithmetic under time pressure, with a scientist telling them in an annoyed voice when they got it wrong. And they manipulated the test to make sure that the participants got it wrong most of the time. They looked at brain activity, as well as heart rate, blood pressure, and a stress hormone called cortisol. They even asked the subjects how stressed out they felt. And then they looked at their brains.

What we've got here is a picture of activation in an area of the brain called the amygdala, usually associated with fear and anxiety, but also associated with learning and stress. Activation during social stress was higher in people currently living in cities. This could be the result of several factors, urban dwellers often have to have a heightened awareness of their surroundings. They may have higher stress jobs. Regardless, it looks like here people living in urban environments show increased amygdala activity in response to social stress, though what that MEANS, we can't really say (the participants didn't report themselves as feeling more stressed).

Here is a figure showing the effects of urban UPBRINGING, regardless of current location. In this study, the participants who had been raised in a city showed increased activation in the anterior cingulate cortex, an idea of the brain involved in stress regulation. I'm not sure what this means, and the authors don't really claim to know either. It could be that people raised in urban environments have brains that are more "stressed out" in response to stress, but it could ALSO be that their brains are better at clamping down on a stress response. Again, the participants showed no difference in stress reporting and brain activity is...just brain activity. Without something showing a difference in behavior, we don't know what that may mean.

The authors concluded that they had found neural mechanisms for an environmental risk factor for mental illness in an urban environment. Me, I'm not so sure.

Now there are many caveats that you need to keep in mind here. The first is: this is just another brain scan study. And ANYTHING can change your brain activation, your gray matter, etc, etc. Heck, breakfast changes your grey matter, so I should certainly hope that city living would do at least that much. The changes are small and may not mean much in the grand scheme of things. And what does this change in activity MEAN? We don't know what the change in activity is doing, what effects it's having. There were no differences in behavior, blood pressure, etc, etc. Without a behavior to go with it, it's just a brain scan showing increased activity, and very little can be concluded from it.

Secondly, fMRI data has a lot of issues with it, not the least of which is the over-reporting of false positives and the under-reporting of negatives. Are these the only two places where they found differences? What about other areas? What does the LACK of difference in other areas mean compared to what they found? This is not because the authors meant to distort their findings (I'm sure they didn't), it's more of an issue of how fMRI data in general gets studied and written up.

Third, they didn't state whether the city dwellers and country dwellers differed in things like life stress. It appears that they didn't differ in physical measures (of hormones like cortisol) or subjective measures of stress (how stressed do you feel right now). But perhaps the measures of stress they were looking at here are not the measures of stress that people are normally exposed to (after all, most people don't have to do arithmetic out loud). People in cities have more than just population pressure acting on them. Did the study participants have more stressful jobs? Did they have more financial stress? None of these things were recorded and they could have substantially affected the outcome. Not only that, they were looking at social stress. How is social stress affected by things like internet use and social networking? Could this give more of a 'feel' of the city in terms of more constant social interaction?

Finally...these people were not mentally ill. In fact, they deliberately chose the most normal people possible (young and college age Germans, which has other issues associated with things like less social and economic disparities, etc). So while they talked about how this difference in brain activation might relate to mental illness, in deliberately choosing people who are NOT mentally ill, they may be seeing a smaller change, or they may be seeing one indicative of a brain resistant to mental illness. The authors claim that the higher activation in the amygdala may provide a mechanism for the triggering of some psychiatric disorders, accounting in some measure for increased psychiatric diagnoses in cities. But none of these people HAD psychiatric disorders triggered by living in cities. This isn't a longitudinal study showing that those with higher amygdala activity and anterior cingulate activity developed psychiatric disorders over time (now THAT would be some proof there). It's a snapshot. In time. Of a small sample of people showing higher amygdala and anterior cingulate activity associated with city living. What does that prove about their mental health or even their stress levels? Not much.

So is city living driving you crazy? I don't think so. I certainly don't think this study proves it. What I'd like to see is a longitudinal study showing differences in development of psychiatric disorders associated with living in cities, a difference not related to access to care, socio-economic stress, etc, etc. Brain scans are all well and good, but they aren't psychiatric disease. I do think that this study shows differences in social stress processing, but until we know what that means, and have the behavioral data to back it up, I'm inclined to think that there may be stronger influences to mental illness in cities than the activity of your anterior cingulate.

Lederbogen, F., Kirsch, P., Haddad, L., Streit, F., Tost, H., Schuch, P., Wüst, S., Pruessner, J., Rietschel, M., Deuschle, M., & Meyer-Lindenberg, A. (2011). City living and urban upbringing affect neural social stress processing in humans Nature, 474 (7352), 498-501 DOI: 10.1038/nature10190