When I was a child (oh, let me be honest: until the age of about seventeen), I was overweight. I was not clinically obese (often defined as 30 percent higher than recommended body mass index), but I was clearly overweight. My parents were not overweight; my siblings were not overweight; indeed, no one in my extended family was overweight. So, why was I? The answer is straightforward: I found the sight, taste, and smell of high-calorie foods appealing, I thought about high-calorie foods even when they weren't in front of me, and I could not resist grabbing whatever high-calorie food was available. In short, I liked to eat. What I didn't like was controlling my eating behavior: I didn't avoid being in the company of food, I didn't avoid thinking about food, and I certainly didn't resist the temptation to reach for food when it was available.

Psychologists often call this a failure of cognitive control, and it is a complex phenomenon. It involves controlling distractions from the environment (e.g., the sight of an ice cream cone), controlling how irrelevant thoughts intrude on ongoing behaviors (e.g., thoughts of ice cream cones), and controlling responses when temptation hits (e.g., not reaching for the cone when it is offered). Indeed, much of the research in my laboratory concerned with cognitive control has been motivated by this tripartite division of control processes: preventing distraction during perception, preventing distraction from internal thoughts, and preventing unintended and irrelevant behavior. Behaviorally, it is possible to distinguish among these three kinds of cognitive control using well-designed experimental tasks in the laboratory.

The distinction among these processes is underscored by neuroimaging research that reveals different patterns of brain activation that accompany each kind of cognitive control. Together, largely with former students Tor Wager, Derek Nee, and Marc Berman, we have amassed a good deal of evidence indicating that cognitive control is not monolithic; it depends on multiple processing systems, but it also depends on some common mechanisms that are enlisted by all these systems. An important contribution to understanding the commonalities and differences among mechanisms of cognitive control comes from brain imaging evidence.