Will an escape to the country keep you sane?

Edward Carr, University of Cambridge School of Clinical Medicine, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0SP

In Nature this week, Meyer-Lindenberg and colleagues report an intriguing link between urban upbringing and the neural response to performing tasks under stress (1).  Whilst there are a number of epidemiological studies linking a higher rate of mental illness in cities, this is the first paper to identify a neural pathway that could explain the difference.

The German group used blood-oxygen-level-dependent (BOLD) fMRI to scan volunteers whilst they were performing mental tasks, with or without social stress.  Social stress was delivered using the Montreal Imaging Stress Task (MIST) (2).  MIST is a series of arithmetic tasks where the difficulty is set for each volunteer individually, such that success rates are 25-40%.  A highly arithmetic volunteer is given harder questions than a less arithmetically able one.  During the test, “study investigators provided further negative feedback … through headphones”.  Imagine your worst supervision ever, in an MRI machine!

Correlation coefficients were generated between local brain activity, as shown by fMRI, and an ‘urbanicity score’, which akin to pack years for smoking, is a numerical summary of the exposure to city living.  Between the ages of 0 and 15, the number of years lived in each setting were multiplied by a factor (city [x3], town [x2] and rural setting [x1]) and then added.  The range was 15 (15 years in a rural environment) to 45 (15 years of city dwelling).

Current urbanicity correlated with amygdala activation during the social stress task and the total urbanicity score correlated with perigenual anterior cingulate cortex (pACC) activation.  Neither of these correlations were observed in other fMRI studies without the social stress component.  The amygdala responds to environmental threat and the pACC is involved in the regulation of the stress response.

In summary, this is the first study to show, using neuroimaging, that individuals with different urban-rural backgrounds process social stress differently.  Whilst the pACC and amygdala are ideal candidates to mediate the difference in prevalence of mental illness between town and country, exactly how the environment alters these neural responses merits further study.

References: 

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

2. Dedovic K, Renwick R, Mahani NK, Engert V, Lupien SJ, Pruessner JC. The Montreal Imaging Stress Task: using functional imaging to investigate the effects of perceiving and processing psychosocial stress in the human brain. J Psychiatry Neurosci 2005 Sep;30(5):319-325.

Story image from Wikimedia Commons