Pitt Researchers Demonstrate Human Brain's Natural Mechanism For Guarding Against Errors

"Our research shows the brain has its own built-in system for detecting competition between two possible yet incompatible responses to a situation," explained Cameron S. Carter, M.D., associate professor of psychiatry and psychology. "When this system detects the conflict, it provides a signal that the brain may use to pay more attention and avoid the error."

The specific area of the brain linked to error-checking is the anterior cingulate cortex (ACC), which is located on the inner surface of the frontal lobes, in the middle of the front part of the brain.

In the Pitt study, researchers used event-related fMRI to look into the brains of 13 people while they performed variants of the Continuous Performance Test designed both to increase error rates and to manipulate competition between possible responses. Event-related fMRI is a new imaging method that allows researchers to acquire images on a trial-by-trial basis during mental tasks. One such test consisted of subjects watching a series of numbers and looking for a specified target -- an "X" immediately following an "A" -- and pressing one of two buttons. A button on the left was pressed each time the target appeared and one on the right for every other combination. Dr. Carter and his colleagues noted a transient increase in ACC activity during incorrect responses, a reaction that had been seen previously in studies of brain electrical activity and attributed to the ACC. However, they also found that there was increased ACC activity during correct responses on trials where! ! response competition occurred. This leads them to believe that the primary contribution of the ACC to performance checking may be to detect response competition rather than to detect just errors, and thus serve as the brain's "how you are doing" monitor.

"The brain knows how to organize itself to implement task instructions," commented Dr. Carter. "This is called executive control. Some tasks are routine and don't require much executive control, while others require a lot of control. Under these circumstances, response competition may occur and the ACC acts as an alarm telling the rest of the brain to exert more executive control so performance doesn't deteriorate."

According to Dr. Carter, a task like driving down the freeway is fairly routine for most American drivers. Because the driver is familiar with this situation, the brain does not need to exercise much executive control. But put that same driver onto a freeway in England and driving suddenly takes on a new dimension. The brain now has two competing choices: follow standard procedure and turn into the right lane, or obey the new rules and stay in the left. The ACC detects this competition and tells the brain to pay attention before its lax executive control allows the driver to make a catastrophic error.

"Until now, we didn't know what type of mechanism the brain employed to monitor its own performance and regulate behavior," continued Dr. Carter. "Now that we've found one such mechanism, we can further explore it with the hope of understanding its role in disorders like schizophrenia and depression."

The work was conducted in association with the Center for the Neural Basis of Cognition, a joint project of the University of Pittsburgh and Carnegie Mellon University, and UPMC Health System's Western Psychiatric Institute and Clinic. Other researchers are Todd S. Braver, Ph.D., post-doctoral scholar; Deanna M. Barch, Ph.D., assistant professor of psychiatry; Matthew M. Botvinick, M.D., post-doctoral scholar; and Douglas Noll, Ph.D., associate professor of radiology, all from Pitt, and Jonathan D. Cohen, M.D., Ph.D., associate professor of psychiatry at Pitt and psychology at Carnegie Mellon University.