While the human brain possesses incredible computational powers, it’s surprisingly easy to short-circuit: all it takes is a hectic city street.
“I think cities reveal how fragile some of our ‘higher’ mental functions actually are,” Kuo says. “We take these talents for granted, but they really need to be protected.”
Related research has demonstrated that increased “cognitive load” — like the mental demands of being in a city — makes people more likely to choose chocolate cake instead of fruit salad, or indulge in a unhealthy snack. This is the one-two punch of city life: It subverts our ability to resist temptation even as it surrounds us with it, from fast-food outlets to fancy clothing stores. The end result is too many calories and too much credit card debt.
City life can also lead to loss of emotional control. Kuo and her colleagues found less domestic violence in the apartments with views of greenery. These data build on earlier work that demonstrated how aspects of the urban environment, such as crowding and unpredictable noise, can also lead to increased levels of aggression. A tired brain, run down by the stimuli of city life, is more likely to lose its temper.
Long before scientists warned about depleted prefrontal cortices, philosophers and landscape architects were warning about the effects of the undiluted city, and looking for ways to integrate nature into modern life. Ralph Waldo Emerson advised people to “adopt the pace of nature,” while the landscape architect Frederick Law Olmsted sought to create vibrant urban parks, such as Central Park in New York and the Emerald Necklace in Boston, that allowed the masses to escape the maelstrom of urban life.
Although Olmsted took pains to design parks with a variety of habitats and botanical settings, most urban greenspaces are much less diverse. This is due in part to the “savannah hypothesis,” which argues that people prefer wide-open landscapes that resemble the African landscape in which we evolved. Over time, this hypothesis has led to a proliferation of expansive civic lawns, punctuated by a few trees and playing fields.
However, these savannah-like parks are actually the least beneficial for the brain. In a recent paper, Richard Fuller, an ecologist at the University of Queensland, demonstrated that the psychological benefits of green space are closely linked to the diversity of its plant life. When a city park has a larger variety of trees, subjects that spend time in the park score higher on various measures of psychological well-being, at least when compared with less biodiverse parks.
“We worry a lot about the effects of urbanization on other species,” Fuller says. “But we’re also affected by it. That’s why it’s so important to invest in the spaces that provide us with some relief.”
When a park is properly designed, it can improve the function of the brain within minutes. As the Berman study demonstrates, just looking at a natural scene can lead to higher scores on tests of attention and memory. While people have searched high and low for ways to improve cognitive performance, from doping themselves with Red Bull to redesigning the layout of offices, it appears that few of these treatments are as effective as simply taking a walk in a natural place.
Given the myriad mental problems that are exacerbated by city life, from an inability to pay attention to a lack of self-control, the question remains: Why do cities continue to grow? And why, even in the electronic age, do they endure as wellsprings of intellectual life?
Recent research by scientists at the Santa Fe Institute used a set of complex mathematical algorithms to demonstrate that the very same urban features that trigger lapses in attention and memory — the crowded streets, the crushing density of people — also correlate with measures of innovation, as strangers interact with one another in unpredictable ways. It is the “concentration of social interactions” that is largely responsible for urban creativity, according to the scientists. The density of 18th-century London may have triggered outbreaks of disease, but it also led to intellectual breakthroughs, just as the density of Cambridge — one of the densest cities in America — contributes to its success as a creative center. One corollary of this research is that less dense urban areas, like Phoenix, may, over time, generate less innovation.
The key, then, is to find ways to mitigate the psychological damage of the metropolis while still preserving its unique benefits. Kuo, for instance, describes herself as “not a nature person,” but has learned to seek out more natural settings: The woods have become a kind of medicine. As a result, she’s better able to cope with the stresses of city life, while still enjoying its many pleasures and benefits.