Brain Development Positively Impacted by Greener Neighborhoods

FEBRUARY 27, 2018
Matt Hoffman
Payam Dadvand, MD, PhD
Lifelong exposure to greener communities in schoolchildren is positively associated with gray matter volume in the brain, according to new study data.

Results showed lower gray matter volume in the left (cluster size, 1980 voxels [6.7 mL]; P <.0005) and right (cluster size, 3233 voxels, [10.9 mL]; P <.0005) prefrontal cortex and in the left premotor cortex (cluster size, 1138 voxels [4.5 mL]; P <.0005), as well as with white matter volume in the right prefrontal region, in the left premotor region, and in both cerebellar hemispheres.

The study, led by Payam Dadvand, MD, PhD, an assistant research professor at ISGlobal in Barcelona, Spain, utilized a patient subcohort from the Brain Development and Air Pollution Ultrafine Particles in School Children (BREATHE) project. It included 253 schoolchildren aged 7 to 9 years over a 12-month period, using 3-D magnetic resonance imaging (MRI) to assess brain volume.

“We identified several brain regions that had larger volumes in urban children with higher lifelong exposure to residential surrounding greenness,” Dadvand and colleagues wrote. “Brain regions whose volumes were increased in association with better cognitive test scores partly overlapped with some of the regions associated with greenness. In addition, peak volumes in some of the clusters associated with greenness also predicted better scores for some cognitive tests.”

Investigators used normalized difference vegetation index (NDVI) for all participant addresses since birth to determine the surrounding ‘greenness’ of the neighborhood. They used the NDVI average in a 100 m buffer around the participant’s address to define residential surrounding greenness, using a 500 m buffer as the variable.

The study also measured 3 categories of cognitive function—working memory (2-back d’), superior working memory (3-back d′), and inattentiveness (ANT HRT-SE). The data showed that higher gray matter volume was associated with smaller ANT HRT-SE values (less inattentiveness), as well as higher d’ values in 2-back and 3-back tests.

Gray matter clusters that were linked with greenness overlapped with those associated with cognitive outcomes at the dorsal prefrontal cortex, with an overlap of 37.4% for ANT HRT-SE, 22.2% for 2-back d’, and 32.2% for 3-back d’, relative to the greenness exposure clusters, and 6.6%, 6.3%, and 5.6%, respectively, relative to the cognitive test clusters.

Better ANT task and n-back test performances were associated mainly with greater white matter volumes in the cerebellum, brainstem, thalamus, part of the parietal lobe, the hippocampus, and the sensorimotor cortex—extending to the premotor cortex. Overlap between gray matter clusters associated with greenness and those associated with cognitive outcomes overlapped at the cerebellar white matter was 51.2%, 17.0%, and 64.2% for ANT HRT-SE, 2-back d’, and 3-back d’, respectively, relative to greenness-associated clusters, and 1.3%, 1.2%, and 2.6%, respectively, relative to the area of the clusters associated with the corresponding cognitive test.

“As the first investigators to evaluate such an association, we did not have an a priori hypothesis about specific brain regions that might be affected by exposure to residential greenness,” Dadvand and colleagues wrote. “However, considerable consistency existed between the regions in white and gray matter that were identified to be associated with greenness exposure in our principal substudy. For all cortical regions found to be associated with greenness exposure (with the exception of the left prefrontal cortex), we also observed changes in their adjacent white matter region.”

They noted that additionally, the clusters associated with greenness had peak volumes positively associated with working memory, and inversely linked with inattentiveness, which is in line with previous evidence related to the impact of premotor and prefrontal areas on the dorsal attentional network.

“A recent review noted that evidence from MRI studies suggests that children and adults with [attention-deficit/hyperactivity disorder (ADHD)] have lower prefrontal and premotor cortex and cerebellum volumes than those without ADHD,” Dadvand and colleagues wrote. “Consistently, we observed negative associations of inattentiveness with volumes of cerebellar vermis and hemispheres (supporting substudy I) and with peak values of greenness exposure–related clusters in cerebellar hemispheres and prefrontal cortex.”

They did note, however, that the latter associations lost statistical significance after controlling the data for age, sex, and maternal education.

“Our findings provide new perspectives on how connections with the natural environment could potentially contribute to brain development,” the authors wrote. Further studies will be required to confirm the findings in other populations, settings, and climates, as well as to determine if “developmental effects on the structure of the brain contribute to associations between greenness exposure and cognitive development remains an open question to be evaluated by future studies.”

The study, “The Association between Lifelong Greenspace Exposure and 3-Dimensional Brain Magnetic Resonance Imaging in Barcelona Schoolchildren,” was published in Environmental Health Perspectives.

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