Bratman GN, Hamilton JP, Hahn KS, Daily GC, Gross JJ. Nature experience reduces rumination and subgenual prefrontal cortex activation. Proc Natl Acad Sci U S A. 2015;112(28):8567-8572.
Design & Participants
Randomized between-group comparison of a 5.3 km solo walk in either a grassland-and-oak nature park or busy urban street in Palo Alto, California. Each participant was given a smartphone with GPS tracking was given to monitor their location and take pictures of their experience, in order to ensure compliance with study instructions and walking route.
All participants were urban residents (n=38, 18 female, mean age 26.6 years) of the San Francisco Bay metropolitan area, with no history of neuropsychiatric disorders or current psychotropic medication use. They were randomly assigned to either the nature- or urban-walk group. No significant differences in mean age or gender distribution of the groups was detected.
Immediately before and after the walk, participants completed a psychometric and biomarker assessment of their experience.
- Psychometric: The Reflection-Rumination Questionnaire (RRQ) is a validated scale for measuring mental rumination, which is an associated antecedent of clinical conditions like depression and anxiety.1
- Biomarker: Arterial spin-labeling MRI neuroimaging measured subgenual prefrontal cortex (sgPFC) neural activity via proxy cerebral blood flow. Increased sgPFC activity is associated with experiences of sadness, social withdrawal, and negative self-reflection, all of which are linked to rumination and its resultant conditions.2
Heart and respiration rates were taken during neuroimaging to account for any individual differences in physiological response to walking; no between-group physiological differences were detected before or after the walks.
Key FindingsStatistically significant differences between the nature- and urban-walking groups for both psychometric and biomarker analysis, demonstrating subjective and objective changes in psychophysiologic rumination experience. Mean RRQ scores were significantly decreased following the nature walk [t(17)=−2.69, P<0.05, d=0.34] but were unchanged after the urban walk. Similarly, sgPFC bloodflow was significantly decreased in the nature walk group [t(15)=−6.89, P<0.0001, d=1.01] but was unchanged for the urban-walk group.
Commentary & ImplicationsThis is the first study to demonstrate neuroimaging and corresponding psychological changes in response to real natural vs built environmental exposures. Other studies have reported similar fMRI results after viewing natural vs built images in a lab, 3 and there is an extensive body of literature using animal models that demonstrates beneficial neurostructural and neurofunctional changes from living in more ‘natural’ contexts.4 In addition, the most substantial fMRI study on this topic shows healthier stress responses in other brain areas (ie, pACC*, amygdala) of adults who grew up in rural areas than adults that grew up in a city; these results were consistent after controlling for participants’ current living location.5 Taken together, these studies showcase the objective changes in the functional brain that result from contact with nature.
Of course, these objective changes in the brain give rise to the positive subjective experiences of natural environment exposure that have been reviewed extensively in the literature.6,7,8 Evidence is showing that nature-based experiences are legitimate and useful complementary therapies for addressing mental health conditions like depression and ADHD.9,10 In addition, contact with nature also increases positive mental health experiences. Spending time in nature can improve a patient’s sense of vitality,11 life satisfaction,12 and subjective well-being.13 These aspects of “positive psychology” are increasingly touted in health promotion disciplines14 and are recognized as important components of increasing overall health as well as effectively managing and treating mental health conditions.15 Though it is in its early stages, the contribution of environmental factors to this salutogenic approach to mental health care is beginning to be recognized.16
One facet of this positive, health-promoting quality of nature is the ability to inspire and instill a sense of awe. Awe is a feeling of grandeur and appreciation for things bigger than oneself, and as reviewed in the August 2015 issue of Natural Medicine Journal, it has the capacity to modulate immune system function and reduce pro-inflammatory cytokines.17 A recent study suggests that the awe generated by nature helps us “put things in perspective” and allows us to realize how small yet simultaneously interconnected we are in a greater universal context.18 It is possible that this relative perspective helps us transcend our own personal concerns and works to break the cycle of self-doubt and rumination that leads to mental health conditions. The study also found that nature-inspired awe was more likely to induce pro-social behavior, essentially meaning that people behaved as better people toward others. This is exciting because it means that nature-inspired awe is a truly “biopsychosocial” health promotion factor.As for limitations of the current study, it must always be addressed than any “field study” contains a near-infinite number of variables that may be influencing outcomes. It is not possible to list all of the ways that the natural and urban settings in this study differed, or isolate which of those variables are the causative agents. However, it is important to recognize that to attempt to do so would be missing the point. Environmental settings in which people live, work and play are not isolated biochemical agents that lend themselves to a randomized, double-bind, placebo-controlled trial. They are complex matrices of experience and engagement that have a constant input with us on every level. We are just beginning to appreciate and include this awareness in our healthcare paradigm.
For the clinical practitioner, it is useful to have a wide range of tools when working with patients. Getting patients outside and into a natural environment helps clear the mind, revive the body, and restore the spirit. All in a way that works with “the healing power of nature” and doesn’t have to come in a pill.
Supportive evidence continues to accumulate showing that spending time in nature is a valuable and beneficial activity for improving mental health, particularly in urban residents for whom exposure to natural environments may be limited.
*pACC = Perigenual Anterior Cyngulate Gyrus, a region of the brain in which increased activity is associated with healthy cognitive and affective processing, and decreased activity is associated with mental-emotional pathology.19