Urbanizität als Risikofaktor für psychische Störungen: neuronale Korrelate

Urbanicity is an established risk factor for mental illness. This has been proven in large population studies especially for schizophrenia, but also for depression and other psychiatric diagnoses. In the search for causality, imaging studies have increasingly been carried out in the last years. Heterogeneous neuronal correlates of the risk factor were shown. The aim of our study was to carry out a multimodal investigation of growing up in an urban environment on a large cohort (n=625) to make a comparison with previous studies and to minimize previous limitations. The VBM analysis did not show significant results as main effect. In a gender interaction, a positive correlation of urbanicity score and grey matter volume in the area of the entorhinal cortex could be demonstrated in male subjects at trend level. Also at trend level, a negative correlation with the urbanicity score in the area of the visual cortex, the cingulum and the precuneus could be found for the cortical thickness. Examination of gyrification did not yield any significant results. DTI showed a reduced FA in the ROI analysis of the uncinate fasciculus and the inferior frontooccipital fasciculus. Functional imaging (fMRI) showed a positive correlation between growing up in an urban environment and activation of the left amygdala by an emotional face processing task. Our study fits into the heterogeneity of previous studies. No significant results could be found in the VBM and SBM in the area of the DLPFC, which has often been described as affected. Furthermore, no global influence of growing up in an urban environment was shown for cortical thickness, but rather localized effects. The DTI analysis also produced different localizations than the comparison study. As in other studies, an altered activation of the amygdala could be demonstrated in fMRI. Related to cortical thickness, two affected systems have been discussed. First, a trend was found in the visual cortex. A possible explanation for this is the sensory perception of the environment, which differs between city and countryside. Environmental characteristics, such as green surroundings or noise pollution, could contribute to the risk of mental illness in the city. But it is also possible that the visual system is involved in processing emotions and thus in the psychopathology of various diseases. Second, two trends were found that can be associated with the default mode network (DMN). This is involved in coping with stress and thus also in the psychopathology of various disorders. In DTI, reductions in FA were found in a frontolimbic and a frontooccipital network. The frontolimbic system can be associated with stress processing and emotion regulation. In addition to the occipital cortex, the frontooccipital network also connects other cortical areas with the prefrontal cortex and has a wide range of functions. Both the frontolimbic and frontooccipital networks have been shown to be involved in various mental disorders. As in some previous studies, altered activation of the amygdala was found in connection with growing up in an urban environment. The hyperactivation by emotional stimuli found here has been specifically associated with schizophrenia and symptoms of depression. The variability of urbanicity represents an explanation for the heterogeneity of the study results. Previous studies were carried out with population-based values that did not take this variability into account. There are many aspects that could be responsible for the risk posed by urbanicity. These include social and socio-economic problems, environmental quality, medical care and much more. Ultimately, growing up in an urban area as a population-based variable is too imprecise to include all these aspects. Stress experiences and their processing could play an important role in the effect of urbanicity as a risk factor. In order to mitigate the effect as a risk factor, the goal must be to avoid harmful stress experiences. In addition to social stress, stressful experiences due to poor environmental quality were also described. The political and social tasks that result from this are large. Nevertheless, dealing with them is of great relevance in view of increasing urbanization and the social importance of mental disorders.