The natural environment at home influences the anatomy of the brain

Relation

Kühn S, Düzel S, Eibich P, et al. Searching for characteristics that constitute an “enriched environment” in humans: Associations between geographical features and brain structure.Scientific Rep. 2017;7(1):1-8.

Study objective

To determine whether environmental factors of residence have measurable associations with the morphology of specified brain structures.

Design and participants

Spatial association study using functional magnetic resonance imaging (fMRI) brain scans of 341 older adults (mean age 70.1, SD = 3.89; 131 female) living in Berlin, Germany, and geocoded data of 4 land use types (urban green, forest, water). and wasteland) within a radius of 1 km from the participants' place of residence. Participants had no current or previous diagnoses of cardiovascular or neuropsychiatric disease. Land use data were obtained from the European Environment Agency's Urban Atlas dataset. The results were controlled for age, gender, education and retirement income.

Target parameters

Functional magnetic resonance imaging scans of the following brain areas:

• Amygdala: emotionales Regulationszentrum des limbischen Systems, verbunden mit Wut, Angst, Angst und einer erhöhten Stressreaktion
• Perigenualer anteriorer cingulärer Kortex (pACC): ebenfalls Teil des limbischen Systems, assoziiert mit Emotionsregulation, Motivation und Schizophrenie
• Dorsolateraler präfrontaler Kortex (DLPFC): Teil des kognitiven Zentrums des Gehirns, verbunden mit Arbeitsgedächtnis, Planung, Vernunft und Hemmung

Structural equation modeling (SEM) was used to determine the relative amount that each of the 4 land use types exerted on changes in the size and activity of the measured brain regions.

Key insights

Of the 4 land use types tested, only living proximity to a forest had a measurable effect on the 3 brain structures, and of these only the amygdala showed statistical significance (β=0.232, SE=0.090;P=0.010). This result was valid at a radius of 1 km and remained significant when retested at a radius of 500 m and 2 km.

Practice implications

By now it should be clear that exposure to natural environments can benefit mental health, including mood, attention and memory¹and morbidity and mortality rates.²This current study shows this keyanatomicalChanges can occur due to prolonged environmental exposure. In particular, the link between forests and changes in amygdala activity suggests that living in forested areas promotes not only an acute sense of relaxation during exposures, but also increased long-term resilience to negative emotions such as fear and anger by remodeling the brain.

This is not surprising as the neuroplastic capacity of the brain has been recognized for many decades.

This study continues the pioneering work of Lederbogen and colleagues, who showed that an adult's limbic system can be influenced by the greenery around their childhood home.³Essentially, a more rural childhood can benefit how a person's brain (particularly the amygdala and pACC) processes and perceives stress as an adult, many years after they have moved. This is similar to research showing that an activity such as meditation training can have positive effects on emotional reactivity and corresponding limbic system activity that persist years after initial meditation training.⁴With this in mind, where you live could be just as important to developing successful stress management skills as the activities you engage in.

This is not surprising as the neuroplastic capacity of the brain has been recognized for many decades.⁵Since the late 1940s, studies have been carried out in rats showing the effects of “environmental enrichment” on brain structures as well as corresponding behavior, mood and memory.^6.7The importance of appropriately enriched environments is standard practice in zoological environments, with known effects on animal brain structure and function, as well as morbidity and mortality.⁸It makes sense that people are also affected by the environmental context in which they live.

For people, this context is increasingly the urban environment. According to the 2010 U.S. Census, over 80% of the U.S. population lives in an urban area, with projections of continued urban growth.⁹This is very different from the environmental context in which humans evolved and to which we are optimally adapted, according to concepts such as EO Wilson's biophilia hypothesis¹⁰or Ulrich's Psycho-Evolutionary Stress Theory.¹¹The urban environment produces many stressors, including traffic, noise pollution, air pollution and population density, all of which have measurable adverse effects on the cityspirituallyHealth and well-being.¹²The psychophysiological effects of living in the city are known as “urban stress,” a concept coined in 1977¹³and has been well researched since then.^14.15A meta-analysis of 20 studies conducted in 2010 found a 13% to 28% increased odds ratio of mental disorders, including depression and anxiety, for urban residents compared to rural residents.¹⁶Some research has shown that rates of schizophrenia are up to 2.5 times higher in urban versus rural settings, even after accounting for reasons why people with the condition may prefer to move to cities (e.g., better access to mental health services).¹⁷

Although more work remains to be done to understand the complex interplay of environmental and individual factors, it is clear that our environment is more than just a passive part of our experience. They are an integral part of what determines the health of our minds and bodies.

restrictions

This was a cohort study of people living in housing of their choice, not an experimental design. Therefore, it is not possible to assign causality to land use type based on these results. However, this study design is widely used in public health research because it would be unethical and very costly to randomly assign different residence locations and require participants to live there for several years.

Another limitation of the study is the 9-year gap between the land use dataset (2006) and the brain scan data (2015). While the land use type in Berlin does not change very quickly, it is possible that the 2015 land use data could be different and therefore influence the data results.

Finally, this study only looked at 1km radii of participants' home addresses, not where they spent their time or what they viewed. It is possible that their environmental exposure was slightly different than suggested in this study. For example, the study did not measure how much time participants spent outside their homes or looking out of their windows, or how much time was spent in these places. However, given the average age of the participants (70 years), it is likely that a significant amount of time was spent in this location.

Conclusions

This study adds to research evidence that environmental factors influence structural changes in stress-related areas of the brain. Clinicians can incorporate this information into aspects of their clinical encounters that relate to either patient history taking (e.g., “How green is where you live?”) or recommendations for therapeutic benefit (e.g., prescriptions for increased exposure to green spaces).