Hugh Pickens writes "The city has always been an engine of intellectual life and the 'concentration of social interactions' is largely responsible for urban creativity and innovation. But now scientists are finding that being in an urban environment impairs our basic mental processes. After spending a few minutes on a crowded city street, the brain is less able to hold things in memory and suffers from reduced self-control. 'The mind is a limited machine,' says psychologist Marc Berman. 'And we're beginning to understand the different ways that a city can exceed those limitations.' Consider everything your brain has to keep track of as you walk down a busy city street. A city is so overstuffed with stimuli that we need to redirect our attention constantly so that we aren't distracted by irrelevant things. This sort of controlled perception — we are telling the mind what to pay attention to — takes energy and effort. Natural settings don't require the same amount of cognitive effort. A study at the University of Michigan found memory performance and attention spans improved by 20 percent after people spent an hour interacting with nature. 'It's not an accident that Central Park is in the middle of Manhattan,' says Berman. 'They needed to put a park there.'"