Image: JENNIFER JEWETT, Vanderbilt University

Researchers at Vanderbilt University report in today's issue of Nature that they have identified a set of neurons in one region of the brain that recognizes when you have made a mistake. "The work is very important because it shows the cellular basis of self-control," says Sohee Park, a psychology professor at the University. "It gets at really basic questions of psychology and philosophy like the origin of thought and free will." In that respect, it may also shed light on diseases such as schizophrenia and obsessive-compulsive disorder.

Jeffrey Schall and post-doctoral fellows Viet Stuphorn and Tracy Taylor gave macaque monkeys a simple task: visually track a spot on a computer screen. When the monkeys first looked at the screen, the spot appeared in the center; once their gaze was fixed, the spot disappeared and another popped up in the periphery. If the monkey shifted its eyes, it was rewarded with juice. But sometimes, as the monkey was planning to look away, the central spot reappeared. In these cases, the animal was rewarded only if it cancelled its intended eye movements and kept its eyes on the central spot.

During the experiment, Schall and his colleagues monitored the activity of neurons in a region of the brain called the supplementary eye field, located in the frontal lobe, and in a nearby structure, the frontal eye field, which exercises direct control over eye movements. The team discovered that the two areas showed very different patterns of activity. In the supplementary eye field, three types of neurons fired in response to different circumstances. One set acted when the monkey realized it had made the right decision and would receive a reward; another set, dubbed the "oops" neurons, reacted when the animal knew it had made a mistake; and a third responded when the brain received conflicting instructions. In summary, Schall says, "it appears that the neurons in the secondary eye field are monitoring eye movement, not controlling it."