Fig. 1 shows the implications of Eq. 1 for the potential produced by a current dipole consisting of a point current source (current injected into medium, yielding positivities) and sink (current removed from medium, yielding negativities). For any recording contact, the potential may be computed as a linear summation of the two contributions. For more complex configurations of sources and sinks, the recorded potential is the linear summation (i.e., volume integration) of all such contributions. Although this example clearly shows that the fall-off from each individual point source (sink) is inversely related to distance (also see Eq. 3.6, Nunez and Srinivasan, 2006a), it can readily be shown that the corresponding fall-off from a radially-distributed set of sources and sinks (i.e., a sheet or layer of multiple source-sink pairs) approximates a linear function as the radius of the set increases (cf. Tenke et al., 1993).
