Source density analysis of scalp potentials during evaluated action. I. Coronal distribution.

The distribution of source densities (the "Laplacean") of event related potentials (ERPs) over the scalp during a goal-directed task has been derived by a novel method which presents seven samples in a hexagonal array, using an economical computing technique that affords much freedom from artefactual contamination. The task had four phases: waiting for a ball to appear, observing its coordinates and estimating action needed to get it through a goal-mouth, acting and awaiting the outcome, and finally evaluating the outcome as success or failure. Different phases of the task were characterized by significantly different distributions of sources. Failures were distinguished from success to consistent features of the last phase of the ERP. All locations within the reference hexagon (spanning a circle of approximately 12 cm diameter on the scalp) showed the latter features. In control experiments, the effects of response mode and of different cognitive interpretations of the input/output situation were studied. A check showed that with monopolar recording involuntary tongue movements can totally vitiate conclusions in such investigations. The Laplacean derivations proved relatively free of such artefactual contamination.