Local field potential genesis

The local field potential is the low-frequency (roughly below 300 Hz) part of the extracellular potential, and understanding its genesis means asking which transmembrane currents dominate. Synaptic currents — especially slow dendritic postsynaptic currents in the aligned apical dendrites of pyramidal cells — are the principal generators, because they are spatially extended, temporally slow, and often synchronized across many neurons, allowing their dipolar fields to summate. Additional contributions come from calcium spikes, intrinsic subthreshold membrane oscillations, afterhyperpolarizations, and spike afterpotentials; fast action-potential currents contribute mainly to the high-frequency edge and, when many cells fire together, to a spike bleed-through component.

Interpreting the LFP is complicated because it is a mixture: a signal recorded at one site can reflect synaptic activity generated hundreds of microns away and volume-conducted in, and the amplitude is governed by the geometry and correlation of sources rather than by local firing alone. The frequency content is also shaped by tissue and electrode acting as filters and by the 1/f (aperiodic) background against which oscillatory peaks sit.