Sometimes you stop in mid-action, certain you’ve made a mistake. How does your brain know? Where does that message come from?

This week neuroscientists got a little bit closer to answering that question when they isolated the “oops” center in monkeys’ brains. Researchers at Vanderbilt University in Nashville, Tenn., led by psychology professor Jeffrey Schall, say they have located the specific set of neurons in the brain where error recognition occurs.

The area may be part of a larger system that has evolved in the brain to control its own activity as it makes decisions, corrects errors and overrides habitual responses.

Using monkeys in their experiment allowed the Vanderbilt team to monitor brain activity at a level of resolution that is not possible in humans. Schall believes the findings, published this week in the journal Nature, have important implications for mental and neurological illnesses as well as a fundamental human question — do we really have free will?

Monkey See, Monkey Err

The researchers sat a group of macaque monkeys in front of computer screens, monitoring their gaze with an eye-tracking system. A spot appeared on the center of each screen. When the monkey’s gaze was fixed on it, the spot disappeared and a new one appeared on the periphery of the screen.

If the monkey shifted its gaze to the peripheral spot, it was rewarded with juice. During some of the trials, the central spot reappeared while the monkey was preparing to shift its gaze to the peripheral spot, in which case monkeys who canceled the planned eye movement and kept their gaze on the center were rewarded.

As the monkeys performed the task, researchers also monitored neuron activity in a part of the brain called the supplementary eye field. They found three types of neurons in the area. One type acts when the monkey realizes it has made a correct decision and will receive a reward, the second reacts when the monkey becomes cognizant of its mistake, and the third responds when the brain receives conflicting instructions.

A Step in the Right Direction

“This finding is quite important as part of a larger story,” says Michael Posner, director of Cornell University’s Sackler Institute for Developmental Psychology in New York, who was not involved in the research.

Calling the findings “very exciting,” he said they were a step forward in discovering the brain’s regulatory system, which could be very useful in childhood development work, among other areas.

But, Posner points out, cognitive sciences — which investigate the mental mechanisms that underlie perception, thought, action, and emotion — still have a long road ahead. In the past 10 years it has become possible to observe the brain through neuroimaging, but researchers are only just beginning to understand the evolutionary story of these higher mental functions, he says.

“We want to know how things work, but we’re nowhere near answering,” agrees Roger Ratcliff, a professor of psychology at Northwestern University in Illinois. Because studying human brains requires using non-invasive techniques, the work can sometimes be slow going, he says.

Ratcliff also believes that isolating the “oops” center is a step in the right direction, but worries that by identifying where certain functions in the brain occur, researchers sometimes ignore important questions about where information is sent and how these systems evolved. “Most things in the brain involve quite wide circuits, not just a few neurons,” he explains.

Agents Acting on Free Will?

Schall argues that in order to understand how the brain works, scientists must first pinpoint where certain functions occur. “If we are going to understand how the mechanism works, we have to know the individual neurons,” he says.

He hopes his findings will help to develop treatments for people with Parkinson’s and other neurological diseases, as well as for schizophrenics, a majority of whom have shown in clinical studies to have difficulty with executive control of eye movements. He plans to collaborate with another Vanderbilt psychology professor and pharmacologist, Herbert Metzer, on a series of parallel studies using monkeys and people to test the efficacy of anti-schizophrenia drugs.

But apart from the medical implications, Schall’s discovery also raises an interesting question about our notions of self-control. Are we really in control if we are actually programmed to monitor ourselves?

“Our society is built on the premise that we are all agents acting on free will,” says Schall, who says his work is motivated, in part, by a desire to better understand himself. “But my sense is that this is a system we are born with that can probably be adapted.”