Access to Green Space May Benefit Cognitive Function
- Research shows green space is associated with decreases in air pollution, lowered risk of depression, and increased physical activity levels.
- Access to green space was significantly associated with higher scores in overall cognition, psychomotor speed, and attention tasks.
- Healthy older adults without cognitive impairment and access to green space were associated with smaller and healthier brain ventricles.
The beautiful weather in the spring draws us out of our houses, almost begging us to explore. Being out in the sunshine, surrounded by the green of nature, is usually perceived as restful.
But is it providing us with rest? Just what aspect of our minds and bodies are we resting when we’re out and about?
Jimenez et al. (2022) examined the effect of living in an area with lots of green space on cognitive function, referencing the theory of attention restoration developed by Stephen Kaplan (1995).
Attention Restoration Theory
Kaplan traced the attention restoration theory back to William James, who proposed that attention came in voluntary and involuntary forms.
Voluntary attention, now called directed attention (DA), is top-down and effortful attention that we use when focusing on a task we’re choosing to pay attention to. Involuntary attention does not require effort.
It is the form of attention drawn by bottom-up stimuli like shiny objects and pretty colors. Because DA requires that we expend effort to maintain it, this kind of attention can fatigue.
If you’ve ever focused on a task, even one you enjoy doing, for an extended period and discovered that you’re mentally exhausted at the end, then you know this kind of fatigue.
James and Kaplan proposed that involuntary attention can serve as a respite for the mind when our DA is tired. And being out in nature, where there are plenty of interesting things to look at, examine, and grab our involuntary attention, might be providing us with that rest.
The Benefits of Green Space
Jimenez et al. wanted to see if there were health benefits (both mental and physical) to this kind of respite for the mind. They used a subset of the second generation of the Nurses’ Health Study (II), an extensive, longitudinal study that began in 1976 designed to study risk factors for major chronic diseases in women (this study is ongoing).
Jimenez et al. used data from 13,594 women who joined the cohort in 1989. These volunteers completed a series of online cognitive function tests (The Cogstate Battery) to measure psychomotor speed (the speed of thinking), attention, and working memory, all associated with frontal lobe function. In each test, the participant sees the image of a playing card face down on the computer screen and a clickable button marked “yes.”
Several aspects of cognitive function can be assessed by varying the specifics of the test. For example, in the “Detection” task, the participant is asked to click on the “yes” button as quickly as possible, as soon as the card turns face up. To measure attention, the task is made a bit more difficult.
The participant is asked to click on the “yes” button if the card flips over and is a red card. And to measure memory, the rules are again modified so that now the participant is asked to click on the button if, when the card flips over, the card is the same as the one presented in the previous trial.
The scores on Cogstate tests have been found to predict early Alzheimer’s pathology, even before cognitive impairment is evident.
Green space was measured with the Normalized Difference Vegetation Index (NDVI), which uses satellite imagery of the earth to measure live green plant canopies. Scores on the NVDI can range from -1.00 to 1.00 with negative numbers corresponding to water, values of 0 to 0.1 for barren rock, sand, or snow, and values of around 0.2 associated with shrubs, and grassland values of 0.6 to 0.8 indicated temperate or tropical rainforests.
Since green space is associated with decreases in air pollution, lowered risk of depression, and increased physical activity levels, researchers also assessed depression (using the Center for Epidemiologic Studies Depression Scale) and physical activity (self-report). They also adjusted for age, race, and socioeconomic state.
They found that having access to green space was significantly associated with higher scores in overall cognition and psychomotor speed and attention tasks but not with learning or working memory tasks. The authors estimated that the improved speed and attention were roughly the equivalent of being 1.2 years younger.
Green Space and Your Brain
Researchers are now looking for associations between exposure to green space and overall brain health. For example, a 2021 study by Besser et al. found that in healthy older adults without cognitive impairment, access to green space was associated with smaller and healthier ventricles in the brain (although the effect only bordered on statistical significance). Enlarged ventricles are an indication of brain cell loss and global brain atrophy.