This definition of CSD is Poisson’s source equation, relating the measured voltage to the amplitude of the underlying current generators. Inasmuch as the Laplacian operator (∇2) is a second spatial derivative, Eq. 4 may be intuitively understood as a spatial analog of F = ma, the well known relationship from classical physics that defines the proportionality between an object’s acceleration (second temporal derivative of location) and the time course of a force applied to it.
