Can the level of prefrontal activity provide an index of performance in humans?

The experiment reported here was aimed at determining whether the level of brain activity can be used as an index of subjects' performance on a temporal task. The discrimination of durations constituted the task. An array of four A's appeared on a screen, and subjects had to decide whether the letters remained on the screen for a short or a long duration as learned in a practice phase. This task allowed us to compare the level of brain activity obtained in correct and incorrect responses. The current density measures recorded over prefrontal areas showed that the level of activity obtained with correct responses was lower than those obtained with incorrect responses. This suggests that a good performance could be the result of an economic, but efficient, information-processing mechanism in the brain.