The monkeys were trained to look at a visual target displayed in different positions on a computer screen, unless they received a stop signal. They were taught not to look at the target after receiving such a signal. The monkeys' eye movements were tracked with enough precision so that they could be correlated with neuronal activity. The monkeys were trained by rewarding them with squirts of juice when they correctly followed instructions.

By requiring the monkeys to inhibit a movement after their brain had begun preparing to execute it, Schall and his colleagues created situations that isolated different types of neural signals. By recording in the ACC while the monkeys responded to these situations, the researchers successfully identified neurons that signaled discrepancies between intentions and actions, what the researchers refer to as errors.

"The elegance of this paper is that they were able to sort out different cognitive components or behavioral components that might be driving neural activity in the cingulate," says Tomas Paus of McGill University, a neuroscientist who was not involved in the study but also investigates this part of the brain.

This methodology allowed the researchers to determine whether activity in the anterior cingulate signaled that the action deviated from what the monkey had intended or signaled that the consequences of the action differed from what he anticipated. "We had a few trials where he did the right movement but we didn't give him juice. We found that many of these neurons also fired following the absence of reinforcement," says Schall. In these trials the monkey's action was correct but the consequence was unexpected. If the ACC were monitoring the actions alone, the neurons would not have responded.

The researchers also found that there was an
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Contact: David F. Salisbury
david.salisbury@vanderbilt.edu
615-343-6803
Vanderbilt University
2-Oct-2003