Fig. 2.

Schematic illustration of the relationship between MEG primary current source signals and LFP. Inverse solution techniques applied to MEG (or EEG) sensor data estimate the location and magnitude of the primary electrical current sources (J^p) producing the recorded fields. These current sources are associated with the net postsynaptic currents flowing within the long, spatially aligned apical dendrites of large populations of PNs, enabling an interpretation of polarity in terms of the directionality of current flow within the PN dendrites (35, 37–39). The primary sources will also produce volume currents (J^v) and an associated extracellular potential distribution that can be recorded with microelectrodes as LFPs.