Epidemiologists showed decades ago that people raised in cities are more prone to mental disorders than those raised in the countryside. But neuroscientists have avoided studying the connection, preferring to leave the disorderly realm of the social environment to social scientists. A paper in this issue of Nature represents a pioneering foray across that divide.
Using functional brain imaging, a group led by Andreas Meyer-Lindenberg of the University of Heidelberg's Central Institute of Mental Health in Mannheim, Germany, showed that specific brain structures in people from the city and the countryside respond differently to social stress (see pages 452 and 498). Stress is a major factor in precipitating psychotic disorders such as schizophrenia.
The work is a first step towards defining how urban life can affect brain biology in a way that has a potentially major impact on society — schizophrenia affects one in 100 people. It may also open the way for greater cooperation between neuroscientists and social scientists. "There has been a long history of mutual antipathy, particularly in psychiatry," says sociologist Craig Morgan at the Institute of Psychiatry in London. "But this is the sort of study that can prove to both sides that they can gain from each others' insights."
Meyer-Lindenberg works on risk mechanisms in schizophrenia, and previously focused on the role of genes. But although a dozen or so genes have been linked to the disorder, "even the most powerful of these genes conveys only a 20% increased risk", he says. Yet schizophrenia is twice as common in those who are city-born and raised as in those from the countryside, and the bigger the city, the higher the risk (see 'Dose response?').
The article goes on to describe some brain scan experiment in which a lovely young science lady with lots of dark hair and dark eyes "scolds" subjects while they do arithmetic, which sounds like something out of an Austin Powers movie. I can no more make sense of brain scan experiments than I can make sense of recipes so I won't comment on the experiment.
But, there are a few problems with attributing schizophrenia to "stress." The first is that "stress," while it definitely exists, can be used as one of those all-purpose hand-waving explanations. That doesn't mean that it's wrong, but I tend to have a prejudice against it.
The second is that schizophrenia is so catastrophic from a Darwinian point of view -- it ruins the lives of roughly 1% of the population, but generally not until after their families have almost fully invested in their upbringing -- that it deserves some careful explanation.
Third, it's not at all clear to me that we stress out more over stuff that wasn't around during the evolutionary past. Lots of people stress out over snakes and spiders, but people seem to get fairly used to, say, driving 75 mph on the Ventura Freeway. A few weeks ago, I got a cell phone call from some family friends who had a flat tire on the freeway, so I drove over to stand upstream from them and glare at drivers while they were changing it by the side of the freeway. From that perspective, a few feet from cars roaring past, the entire idea of driving on the freeway seems like utter madness. I drove home very slowly on surface streets. But the next day I was driving 75 mph down the Ventura Freeway with no more thought in my head than: "How come I didn't like Led Zep as much in the 1970s as I do now? Black Dog is awesome!"
Fourth, if city life correlates with schizophrenia, why stress instead of infection as a potential cause? Disease burden was such a problem for city dwellers until quite recently that, for example, sub-Saharan Africa had very few cities. People in Africa had to live spread out in small villages or they'd get sick and die.