Analyzing EEG scalp current density using the Hjorth estimator

Scalp current density (SCD) measurements can be used to identify sources and sinks of electrical current on the scalp. We derive a SCD estimator from the Laplacian equation and compare it to the Hjorth estimator. It is clarified that the Hjorth estimator is the weighted average of the directional differences while the Laplacian estimator represents the summation of the second derivatives.