I'd like to tell you a story about a routine of modern life that is really bad for your brain. Everybody performs this activity - sometimes multiple times a day! - and yet we rarely realize the consequences. In 2008, scientists at the University of Michigan did a very clever study illuminating how this activity led to dramatic decreases in working memory, self-control, visual attention and positive affect. Other studies have demonstrated that people who are less exposed to this activity show enhanced brain function. They are better able to focus and even recover more quickly in hospitals.
What is this dangerous activity? It isn't the internet. In fact, the cognitive decreases caused by this activity are much more dramatic than anything that's been linked to the web or computers. (As I recently noted, many studies that look at the effect of various computer activities on the brain have found cognitive enhancements.) Instead, the activity I'm referring to is walking down a city street. When people walk down the street, they are forced to exert cognitive control and top-down attention, and all that mental effort takes a temporary toll on their brain. Just consider everything your brain has to keep track of as you walk down a busy thoroughfare. There are the crowded sidewalks full of distracted pedestrians who have to be avoided; the hazardous crosswalks that require the brain to monitor the flow of traffic. (The brain is a wary machine, always looking out for potential threats.) There's the confusing urban grid, which forces people to think continually about where they're going and how to get there.
The reason such seemingly trivial mental tasks leave us depleted is that they exploit one of the crucial weak spots of the brain. A city is so overstuffed with stimuli that we need to constantly redirect our attention so that we aren't distracted by irrelevant things, like a flashing neon sign or the cellphone conversation of a nearby passenger on the bus. This sort of controlled perception - we are telling the mind what to pay attention to - takes energy and effort. The mind is like a powerful supercomputer, but the act of paying attention consumes much of its processing power.
Based on this data, it would be easy to conclude that we should avoid the metropolis, that the city street is a hazardous place. (In fact, I could even make the case that it's better for the brain to stay home and surf the web than go for a stroll in the city.) But I think that would be a shortsighted argument, based on a limited reading of a limited data set. And that's because we also know that cities are enormously valuable. All that human friction leads to an extremely valuable kind of exchange. (Jane Jacobs, in her seminal work The Death and Life of Great American Cities, argued that every healthy city was defined by its ability to concentrate and facilitate social interaction. She saw the busy sidewalk as an improvisational "ballet," in which information freely flowed between city dwellers.) In other words, we're learning from each other and sharing ideas. This helps explain why, as recently noted by Edward Glaeser, "per capita productivity increases by 4 percent as population density rises by 50 percent."
The lesson, I think, is that everything is a cognitive tradeoff. The city street forces us to exert top-down attention, and that leads to measurable decreases in mental function. On the other hand, the internet, it is argued, encourages a constant state of multitasking and distraction, and that leads to an intellectual shallowness, as we lose the ability to focus for extended tracts of time. My hunch is that the online world will, before long, come to seem as inevitable and necessary as the metropolis. Why? Because the value it provides far outweighs the cognitive costs (which may or may not exist.) And this is why I'm wary when the brain/mind becomes the main criterion for discussing the value of the internet. Such an approach is roughly equivalent to thinking about cities solely in the narrow terms of a few attentional lab tests.
PS. This doesn't mean you can't ameliorate a few of these negative tradeoffs. That's why New York City has Central Park - your prefrontal cortex needs a break - and why it's still important to read novels in the age of Google.
