Dipoles

Current in the brain is not like current through a wire, therefore you cannot express it in Amperes alone. You can either express it as current density (i.e., current per unit of volume) if you compute a distributed source reconstruction or as dipole moment for a sparse source reconstruction. A current dipole consists of a source at the dendrite and a sink at the soma (or the other way around, depending on whether it is an exitatory or inhibitory synapse). The current source and sink together form the dipole. The distance between source and sink determine the impact that the current generator has on the secondary currents in the surrounding tissue. For example, if the distance were zero, there would be no impact at all. Therefore the current is normalised for the distance between the two, and source strength is expressed in Amperes times meters (dipole strengths are typically given in nano amp meters, or nAm). If you make the distance twice as small, and the current flowing from the source to the sink twice as large, the dipole moment will be the same, and the impact on the secondary currents in the surrounding tissue will also remain the same.