On-line source-density computation with a minimum of electrodes.

An economical arrangement is described whereby the Laplacean of the scalp potential distribution delta2V/delta X2 + delta 2V/delta y2 can be approximately computed by analog methods, using a simple adaptation of the input stages of conventional EEG amplifiers. For maximum efficiency the method requires electrodes to be disposed in equilateral triangular arrays. This makes possible the computation of approximate source densities at 7 scalp locations for a total of only 13 electrodes.