This paper is part of NMJ's 2018 Cognition and Mental Health Special Issue. Download the full issue here.
Dadvand P, Pujol J, Macià D, et al. The association between lifelong greenspace exposure and 3-dimensional brain magnetic resonance imaging in Barcelona schoolchildren. Environ Health Perspect. 2018;126(2):1-8.
To assess the relationship between children’s exposure to green space and morphological changes in cognitive areas of the brain.
Design and Participants
This study was conducted as a subset of the BREATHE (Brain Development and Air Pollution Ultrafine Particles in School Children) project in Barcelona, Spain.1 School children (N=253, aged 7-9 y) were followed for a year and evaluated for the volume of their brain and individual brain regions, performance on cognitive tasks, and amount of green space surrounding their residence.
Each participant had MRI scans taken of their brain using high-resolution 3D MRI to measure voxel (ie, 3D pixel) imagery of the gray and white matter of both right and left cerebral and cerebellar areas of interest:2
- Prefrontal cortex, responsible for executive functioning and cognition
- Superior area, associated with working memory and decision-making
- Inferior area (specifically the opercula of insula), associated with conscious thought, motivation, and planning
- Premotor cortex, responsible for planning, learning, and imitation of movement
- Cerebellum, responsible for muscular coordination and balance, as well as attention, learning, and motor skills
In addition, the following tests were conducted every 3 months over a 12-month period, to assess cognitive function and performance in 2 areas:
- Working memory, assessed via a screen-based test (“n-back”) in which participants are asked to identify whether an image in a rolling series is the same or different as an image presented previously.
- Attention, assessed via the screen-based Attentional Network Task (ANT) in which 3 aspects of attention (alerting, orienting, and executive control) are measured via stimulus reaction time with warning cues, spatial cues, and decisional cues, respectively.
Green space around each participant’s residence was determined using normalized difference vegetation index (NDVI) satellite data, a common method for assessing land-use quantity and type. The NDVI for a 100-m radius of all residential addresses from time of birth to the date of MRI data collection was used, and results were averaged and weighted according to duration of residence at each location to create a lifelong greenspace exposure (LGE) value for each participant.
Data was analyzed via separate linear regression analyses for each brain voxel compared to LGE, and aggregated into proximity clusters. Data was also analyzed using the working memory and attention task results as predictors, to identify if higher test scores correlated with increased brain volume in key areas. Participants’ socioeconomic status (SES) was controlled for at both the individual (ie, maternal education) and neighborhood (ie, census-tract Urban Vulnerability Index) level, as was gender and age.
Overall, statistically significant associations were found between all measures, including the following:
- MRI voxel cluster size (indicating enlarged neuroanatomy) was positively associated with improved performance on n-back and ANT scores, demonstrating the relationship between brain structure and function, findings that are consistent with decades of neuroscience research.3
- Improved performance on both n-back and ANT scores was positively associated with increasing amount of LGE, showing that working memory and attention can be affected by quantity of residential green space, which is consistent with previous study results.1
- Amount of LGE was associated with size of MRI voxel clusters in all key brain areas mentioned. Areas of gray matter (right prefrontal cortex, inferior cluster, and left premotor cortex) and white matter (right prefrontal region, inferior cluster, and right and left cerebellum) still demonstrated statistically significant associations with LGE even after controlling for SES. This suggests that for the children participating in this study, there may be a link between quantity of residential green space and volume of anatomical brain structures.
There was also substantial overlap of MRI voxel clusters related to n-back and ANT performance with those areas influenced by LGE, in some cases showing up to a 64% overlap.
Most importantly, the linear regression analyses predicted voxel cluster size effect on n-back and ANT scores in specific MRI voxel clusters influenced by LGE, even after controlling for SES, gender and age, as indicated by regression coefficients:*
- n-back (working memory)
- Right prefrontal cortex, superior cluster, gray matter (regression coefficient: 3.0; 95% confidence interval [CI]: 0.4-5.6; P=0.02)
- Right prefrontal cortex, inferior cluster, gray matter (regression coefficient: 1.6; 95% CI: 0.2-3.1; P=0.02)
- Left premotor cortex, gray matter (regression coefficient: 4.3; 95% CI: 1.2-7.4; P=0.01)
- Left premotor region, white matter (regression coefficient: 3.1; 95% CI: 0.2-6.0; P=0.04)
- ANT (attention)
- Left prefrontal cortex, gray matter (regression coefficient: −127; 95% CI: −2260-7; P=0.06)
This study found that children’s vegetation exposure in their proximal residential environment increased brain volume and improved cognitive function. It is the first study of its kind to show that growing up in a greener home environment has measureable benefit on children’s memory and attention with corresponding evidence of positive changes to related cerebral structures. This data goes a long way toward showing that being in nature is more than just a “feel-good” experience.
Of course, the beneficial qualities of the natural world have been recognized for millennia in cultures all around the world.4 Writers like the 8th century Chinese poet Li Bai have beautifully described the value of “staying on the mountain smiling” for mental and physical health.5 The 19th century naturalist and founder of landscape architecture, Frederick Law Olmsted, famously discussed how “the enjoyment of [natural] scenery employs the mind without fatigue and yet exercises it…and thus, through the influence of the mind over the body gives the effect of refreshing rests and reinvigoration to the whole system."6
This appreciation of the “healing power of nature” began to be investigated as an academic pursuit in the 1970s by researchers such as Rachel and Stephan Kaplan, who developed the Attention Restoration Theory (ART).7 Their theory, which asserts that spending time in nature improves mental fatigue and concentration, has been supported by many studies.8 These cognitive improvements are just one benefit of greenspace exposure, with other validated effects including reduced levels of depression and anxiety (both individually and epidemiologically), improved immune system and cardiovascular function, and reduced mortality.9,10
This data goes a long way toward showing that being in nature is more than just a ‘feel-good’ experience.
This current study is not the first to use brain imaging to measure green space’s positive effects. An article in the February 2018 issue of Natural Medicine Journal discussed a study that used fMRI to detect changes in cerebral anatomy (particularly the amygdala) of adults in Germany relative to their residential green space.11,12 Other studies have shown how being raised as children in urban vs rural settings can influence brain structures related to conflict monitoring, arousal, and hypervigilance13,14 and how such environments may make individuals predisposed or more vulnerable to conditions such as post-traumatic stress disorder (PTSD) and schizophrenia.15,16 These types of studies suggest that the pursuit of optimal health may want to include consideration of environmental context and its impact on mental well-being and development.17,18
Though regression models provide evidence of prediction rather than simply correlation, the design of the study does not permit exploration of the causal mechanisms linking LGE with cognitive changes. While theory and decades of research support ART as a viable explanation for these attention and working memory task results, it is possible other greenspace-related factors like increased physical activity19 and social contacts20 were also involved. This is difficult to determine since the children in this study did not have their physical or social activities recorded for analysis. Future studies may want to include these variables to better understand the causal effects green space has on cognitive development, as has been done with mental health conditions such as depression, anxiety, and psychologic stress.21,22
The amount of greenery surrounding children’s homes has been shown to affect their cognition on an anatomical and functional level, with statistically significant effects on neuroanatomy and related working memory and attentional task performance. This should be noted by clinicians, parents, and teachers as well as anyone who works with pediatric populations with cognitive deficits, academic, or behavioral underperformance, and anyone who wants to maximize cognitive potential. This information may also benefit public health officials, urban planners, and policy makers interested in providing healthier, more optimal public spaces for people to live, work, and play.
*As a reminder, regression coefficients show the linear relationship between two variables—essentially the “slope” of the graph. For example, for every one voxel increase in rPFC-IA, there was a corresponding 3.0 increase in n-back score (in those voxels that were affected by LGE).