In this post from Per Square Mile, Tim De Chant reviews the paper.
"The paper is the first of its kind, merely lifting the corner of a page in what is likely to be a huge tome of neuroscientific discoveries on how urban life affects the development of our brains and how we react to the populous world around us. The study's sample size is somewhat limited, but the results are statistical home runs. And like many pioneering studies, it raises many more questions than it answers.
The Germany-based researchers started by administering a difficult math test to 34 college students. While the students were taking the test, the researchers harangued them about their substandard score or slow progress to stimulate social stress. All the while, functional magnetic resonance imaging machines (fMRI) scanned the students' brains, recording their activity. After the test and scans were completed, the researchers weighed the students' patterns of brain activity against their place of upbringing-big city, small town, or rural area. Subjects who were raised in the city exhibited higher levels of activity in their amygdala, a region of the brain which processes emotion, and cingulate cortex, an area which regulates the amygdala. The results were so powerful that the scientists conducted a follow up experiment to be doubly certain. That study confirmed the findings of the first."