First lady Michelle Obama joins schoolchildren from New Jersey to harvest the spring crop in the White House kitchen garden in May 2013. (Manuel Balce Ceneta/AP)

Children delight in playing in the patches of grass, trees and playgrounds in and around most schools these days and researchers have long documented how important this type of exposure to nature can be to their physical health. But what about their brains?

A study published Tuesday suggests that all that green may boost cognitive development. In a 12-month period, the researchers documented that those exposed to more greenness near their school saw a 5 percent increase in working memory -- a measure of short-term memory -- and a 1 percent reduction in inattentiveness.

"The brain develops steadily during prenatal and early post-natal periods, which are considered as the most vulnerable window for effects of environmental exposure," the authors wrote.

In an article in the Proceedings of the National Academy of Sciences, the researchers wrote that there are many theories about why green spaces may have beneficial cognitive effects: "Natural environments including green spaces provide children with unique opportunities such as inciting engagement, risk taking, discovery, creativity, mastery and control, strengthening sense of self, inspiring basic emotional states including sense of wonder, and enhancing psychological restoration."

The researchers also theorized that the green spaces might have led to more physical activity, which itself is related to higher cognitive functioning, and that the green spaces may reduce pollutant levels, which is also associated with higher cognitive functioning.

This is believed to be the first epidemiological study on the impact of green space exposure on the cognitive development of schoolchildren. It involved 2,593 participants ages 7 to 10 in second to fourth grades in Barcelona.

A previous study, published in PLOS ONE last October, looked at "greenness" near 905 public elementary school in Massachusetts and found a similarly positive effect on student performance. Using satellite imagery, the researchers — from Taiwan, Harvard University, Brown University and elsewhere — were able to determine how thick vegetation was in certain areas; they then compared that with the results of third-grade standardized tests from 2006 to 2012 at the Massachusetts schools. They found that the schools with more greenery had higher test scores even when adjustments were made for race, gender, English as a second language, income, student-teacher ratio and school attendance.

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