A walk in the park is a welcomed respite from the grind of work, especially for city dwellers. Gregory Bratman, a graduate student at the Emmett Interdisciplinary Program in Environment and Resources at Stanford University, agrees that being in nature makes us happier, but he wanted to know why. Is it circumstantial (i.e., getting away from the stresses of work and urban living), or is there a neurological explanation for our joy?

In a new study, Bratman and his colleagues had volunteers walk through two distinct environments. The researchers determined that participants who walked through Stanford’s verdant campus “were more attentive and happier” than those who took a walk along a highway, according to The New York Times.

Bratman gauged happiness based on a person’s tendency to brood. Brooding, for the study, is characterized as “morbid rumination… in which we can’t seem to stop chewing over the ways in which things are wrong with ourselves and our lives.” Bratman then measured broodiness based on blood flow to the subgenual prefrontal cortex of the brain: more brooding, more activity in the cortex. As expected, those who got to enjoy a sunny day in Palo Alto had less activity in the cortex – less brooding.

Bratman’s study is not flawless. There are still questions about what we must do in nature to be happier. We also don’t know whether it’s nature, in particular, that reduces stress and brooding, or just “anything that’s not the city.” But for now, it’s an important first step toward simple solutions to reduce stress.