When I tell people I walk to work every day, I often hear two words in reply: exercise and cost. The virtues of walking over driving as a way to stay fit and save money on gas and parking are widely recognized and need no elaboration from me. But, in addition to being a dedicated pedestrian, I am also a cognitive psychologist, and recent research in my field suggests a less obvious reason to walk to work. This reason also involves exercise and cost, but in relation to our brains, not our waistlines or pocketbooks.

First, let me explain that cognitive psychologists are scientists that study how we perform mental tasks, and some of us are especially interested in how the brain works. Now let me explain what this has to do with how we get to work. The mental tasks involved in driving, especially in unpredictable rush-hour traffic, are much more numerous and complex than those involved in navigating a typical walking route. Tasks include everything from remembering to check our mirrors when backing out of a parking space, deciding to accelerate or decelerate at a yellow light, calculating the space and speed necessary to change lanes, and even trying to read the minds of other drivers to anticipate what they will do.

To perform these and other driving-related tasks, we use our hands, feet, and eyes, but, most important of all — the part that makes all else possible — we use our brains. Therefore, although it might not feel like it, when we drive to work, we actually are getting some exercise: We’re exercising our brains, and exercising them harder than we would if we walked to work. Exercising our brains might sound like a good thing — and, under the right circumstances, cognitive psychological research has shown that it is — so this might seem like a reason for, not against, driving to work. However, there’s a problem, and that’s where the cost comes in.

Exercising our brains, like exercising any other body part, consumes energy. In fact, the brain is an energy glutton. Despite being only about 2 percent of our body weight, the brain consumes about 20 percent of the total energy spent within our bodies. Recently, cognitive psychologists have studied the possibility that, when we use our brains to perform complex mental tasks, we use up a lot of energy and — here’s the cost — this leaves us with less energy to fuel other brain operations afterward.

When brain operations are limited, the obvious happens: Performance on later tasks worsens. Indeed, recent experiments have shown that, when people are made to perform mental tasks on which they have to sustain their attention and control their impulses, they do worse on similar mental tasks they are given later. Many driving- and work-related tasks require sustained attention and impulse control, which suggests driving to our workplace could actually reduce our performance after we get there. We may have more trouble paying attention and inhibiting our impulses, threatening everything from quality control to interpersonal harmony.

Of course, walking to work also consumes energy, potentially reducing the resources available for brain operations. But, if energy must be spent, ask yourself: Would you rather spend it while improving your cardiovascular health, or while sitting in gridlock? Would you rather walk and have something to show for your exercise, or pay both the obvious and hidden costs of driving?