Can ‘green walks’ reduce the urbanisation related risk for mental disorders? PNAS.July.2015

10.07.2015

Increasing urbanisation is considered to be contributing to the aetiology of mental disorders. Our species is moving away from natural environments in an unprecedented way, that too in a short period of time. Proximity to green space is demonstrated to have positive effect on health. Even ‘window views’ of natural elements can atleast temporarily boost memory and attention and provide better impulse control. Urban green spaces also provide such positive effects.

Nature experience repeatedly show positive effect on many functions of our minds. The next question is:  How does that work?

One theory is about rumination which may either create a vulnerability  for mental disorders or generate mental dysfunction directly. Rumination is a self referential thought and is demonstrated to be associated  with negative effect on mental health. The increased attentional focus on negative ideas is maladaptive.  The area in the brain associated with rumination is subgenual prefrontal cortex (sgPFC).

Is it that nature exposure/ experience  make us less self focused? ( like being ‘lost in nature’ around us)?  Would nature experience   reduce rumination and thus improve mental functioning?

Gregory N. Bratmana, J. Paul Hamiltonb, Kevin S. Hahnc, Gretchen C. Dailyd, and James J. Grossc   from Stanford University did an interesting piece of work to answer this question.

38 healthy urban residents with no mental disorders  participated in this study. Baseline rumination measure was collected using  Rumination Questionnaire (RRQ).Regional blood flow was studied using arterial spin labelling (ASL). After baseline measures, each participant was randomly assigned to a 90-min walk in either a natural environment (19 participants) or urban environment (19 participants). After the walk, each participant returned to the laboratory and provided a second, follow-up self-report of levels of rumination  and underwent a second resting-state ASL scan.

 Results

Self reported rumination decreased significantly in nature walk group. Perfusion study show that neural activity in the selected brain area was decreased  in nature walk group . This study show that nature experience reduce both rumination and  sgPFC activation.

It is interesting to note that researchers found changes in activity in perigenual anterior cingulate cortex (pACC) also. This area is considered to have increased reactivity during social information processing in individuals born in urban areas. We already know that risk of psychosis is high with urban birth.   

Comments:

Being in natural environments perhaps bring a sense of belonging  and a state of being one with surroundings which is hard-wired in us. What ever be the mechanisms, it adds to the strength of the idea that we need more green spaces in growing cities. Perhaps all facilities where people are recovering should have green spaces.

The authors argue that  policies that aim to increase the ‘ mental capital’  of our cities would help to  reduce population level mental dysfunctions.

Summary of the article:

Nature experience reduces rumination and subgenual prefrontal cortex activation.

Bratman GN, Hamilton JP, Hahn KS, Daily GC, Gross JJ. Proc Natl Acad Sci U S A. 2015 Jun 29

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