Urban environment and psychiatric disorders: a review of the neuroscience and biology.

Most of the world's population now lives in cities. While living in cities have both health risks and benefits, mental health has been usually considered to be negatively affected by urbanicity. While mental health disorders have complex etiology and multiple causes, it has been shown in multiple observational studies that mood and anxiety disorders are more prevalent in urban centers and incidence has been increasing. In addition, the incidence of schizophrenia is strongly increased in people born and raised in cities. Studies on the effects of urbanicity on the brain, however, are more challenging to conduct, since individual and environmental factors are hard to distinguish. The main objective of this article is to review studies on how specific neural processes mediate those associations between urbanicity and psychiatric disorders and how environmental factors affect genetic regulation (epigenetics). Neuroimaging studies have shown how urban stressors might affect the brain by conducting experiments using functional magnetic resonance imaging (fMRI). There have been demonstrations that urban upbringing and city living have dissociable impacts on social evaluative stress processing in humans. City living was associated with increased amygdala activity and the urban upbringing has been shown to affect the perigenual anterior cingulate cortex, a key region for regulation of amygdala activity, negative affect and stress. In addition, studies on epigenetics have shown associations between exposure to features of the environment and methylation patterns. The goal of understanding how urban environments act as a risk factor for mental disorders may be pursued on several levels. It can be approached by measuring the effects of economic factors (unemployment, socioeconomic status), social condition (social network support), environmental exposures (toxins, air pollution, noise, light), that must be weighed to identify how it contributes to mental disorders.