Nature May Be Key to Strengthening Our Attention

Like many who investigate green space and its impact on the mind, Marcia Pescador Jimenez, Ph.D., was inspired to pursue her research by her own experiences. “I’ve noticed that where I live throughout my life has had a big impact on my health and well-being,” she said. Pescador Jimenez is an assistant professor in the Epidemiology Department at Boston University.

During the COVID-19 pandemic lockdowns, she was at home with her two small children and expected to continue working and focusing. “It was not going well,” she said. “I started going for long walks and some jogs outside. I live in a suburban place, and I was able to see a lot of trees and light coming through the leaves, and I noticed that when I came back, I felt way less stressed and more calm. I was able to work better and be more patient with my kids. I just felt happier.”

Pescador Jimenez’s research has backed up her personal experience. In a cohort study she and colleagues conducted among 13,594 women, increasing green space was associated with higher scores of overall cognition, thinking speed, and attention. The participants’ cognitive functioning was measured through the Cogstate Brief Battery, which consists of four tasks that measure psychomotor speed, attention, learning, and working memory. Pescador Jimenez and her colleagues did not identify an association between green space and learning or working memory, however. Their findings were published in JAMA Network Open in 2022.

An important question when thinking about the link between green space and cognition is the type of cognitive attributes being investigated, Pescador Jimenez pointed out. Studies have shown that green space is associated with improved cognition generally, but not with all metrics of cognition.

So, too, does the type of green space to which individuals are exposed likely impact cognition and well-being differently. Pescador Jimenez co-authored a systematic review and meta-analysis to investigate the association between green space and dementia. They found that living in a place with intermediate access to green space may protect against dementia, but that the same effect was not identified in areas with high amounts of green space. The authors hypothesized that this may be due to adverse effects such as greater social isolation and decreased interaction with neighbors for those who live in very rural areas. The study was published in Current Environmental Health Reports in 2022. The authors noted, however, that potential methodological limitations of the included studies may have affected the results.

Gregory Bratman, Ph.D., M.E.S.M., emphasized the need to understand more about how different types of contact with nature may improve cognitive function, especially when the goal is to use such research findings to impact policy. How do micro-restorative experiences, such as viewing a rooftop garden from afar, impact cognition, for example? Bratman is the director of the Environment and Well-Being Lab at the University of Washington’s College of the Environment.

“In many cases, certain aspects of cognitive function can benefit from those types of nature experiences, but not all,” Bratman said. “And it doesn’t always improve cognition for everyone. Nature experiences differ according to perspectives tied to personal relationships with nature, preferences, lived experiences, and other individual differences.”

Variabilities in measuring green space can prove challenging for researchers and hinder efforts to put research into practice. For example, because green space is linked with lower rates of dementia, increasing green space in neighborhoods where historically disadvantaged people live may help offset their increased risk for the illness, Pescador Jimenez said.

“[B]ut what type of greenness are we really talking about?” she said.

She is working to answer that question now. Using Google Street View images, she and her colleagues are developing green space metrics based on the shrubs, grass, flowers, and trees in an area. The metric will inform how much exposure to specific types of greenness impact health outcomes. Preliminary results suggest that the percentage of trees in an area may reduce residents’ dementia risk. “It’s ongoing work, but it’s something I’m very interested in because it will help us inform policies in very specific ways,” she said.

Lilah Besser, Ph.D., M.S.P.H., research assistant professor at the University of Miami’s Comprehensive Center for Brain Health, said research into green space and dementia has especially exploded over the last few years. That may be driven by more funding to research dementia, but it could also have to do with the positive effects some studies have uncovered. “In my latest literature review, 74% of the papers found at least one positive or beneficial association between green space and brain health,” Besser said. The findings, on which Pescador Jimenez was a co-author, were published in the International Journal of Environmental Research and Public Health in April.

In a previous literature review published in BMJ Open in 2021, Besser found that greater green space was positively associated with various cognitive domains in 10 studies and with improved MRI outcomes (such as regional brain volumes, cortical thickness, and amygdala integrity) in three studies. Additionally, greater neighborhood greenness was associated with lower odds of cognitive impairment in some studies, but greater odds in other studies.

Yet understanding why studies are pinpointing these benefits is more difficult, Besser said. Some studies posit that it is greater access to physical activity, less air pollution, or less stress, while others come to different conclusions.

“It’s too early to say, but personally I think it’s likely more than one mechanism, and that’s what’s kind of exciting,” she said. “People go to green spaces and parks for different reasons. Some want to sit in them, and that lowers their blood pressure. Some want to do physical activities, which we know is a protective factor against a lot of negative outcomes. I think it’s a combination of all these things, and hopefully more research will lead us to more specific answers.” ■

“Emerging Insights Into the Association Between Nature Exposure and Healthy Neuronal Development”

“Residential Green Space and Cognitive Function in a Large Cohort of Middle-Aged Women”

“Is Greenness Associated With Dementia? A Systematic Review and Dose–Response Meta-analysis”

“Diversity of Studies on Neighborhood Greenspace and Brain Health by Racialized/Ethnic Group and Geographic Region: A Rapid Review”