Local field potential

LFP are "extracellular" signals, meaning that they are generated by transient imbalances in ion concentrations in the spaces outside the cells, that result from cellular electrical activity.

This signal is then low-pass filtered, cut off at ~300 Hz, to obtain the local field potential (LFP) that can be recorded electronically or displayed on an oscilloscope for analysis.

The low impedance and positioning of the electrode allows the activity of a large number of neurons to contribute to the signal.

In a simple fluid, with no biological component present, there would be slight fluctuations in the measured potential difference around an equilibrium point, this is known as the thermal noise.

[7] A common method to investigate LFP oscillations that lead to spikes is to calculate spike-triggered averages (see figure).

[8] Part of the low-pass filtering giving rise to local field potentials is due to complex electrical properties of extracellular space.

[9] The fact that the extracellular space is not homogeneous, and is composed of a complex aggregate of highly conductive fluids and low-conductive and capacitive membranes, can exert strong low-pass filtering properties.

Ionic diffusion, which plays an important role in membrane potential variations, can also act as a low-pass filter.