Local field potential: Difference between revisions

'''Local field potentials''' ('''LFP''') are transient electrical signals generated in nervous and other tissues by the summed and synchronous electrical activity of the individual cells (e.g. neurons) in that tissue. 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. LFP are 'local' because they are recorded by an electrode placed nearby the generating cells. As a result of the [[Inverse-square law]], such electrodes can only 'see' potentials in spatially limited radius. They are 'potentials' because they are generated by the voltage that results from charge separation in the extracellular space. They are 'field' because those extracellular charge separations essentially create a local electric field. LFP are typically recorded with a high-impedance [[microelectrode]] placed in the midst of the population of cells generating it. They can be recorded, for example, via a microelectrode placed in the [[brain]] of a human<ref>{{cite journal |last1=Peyrache |first1=A |last2=Dehghani |first2=N |last3=Eskandar |first3=E.N. |last4=Madsen |first4=J.R. |last5=Anderson |first5=W.S. |last6=Donoghue |first6=J.A. |last7=Destexhe |first7=A |title=Spatiotemporal dynamics of neocortical excitation and inhibition during human sleep. |journal=Proceedings of the National Academy of Sciences |date=2012 |volume=109 |issue=5 |pages=1731–1736 |doi=10.1073/pnas.1109895109|pmid=22307639 |pmc=3277175 |bibcode=2012PNAS..109.1731P |doi-access=free }}</ref> or animal subject, or in an [[in vitro]] brain [[Slice preparation|thin slice]].

The local field potential is believed to represent the [[neural oscillation|synchronised input]] into the observed area, as opposed to the [[Action potential|spike]] data, which represents the output from the area. In the LFP, high-frequency fluctuations in the potential difference are filtered out, leaving only the slower fluctuations. The fast fluctuations are mostly caused by the short inward and outward currents of action potentials, while the direct contribution of action potentials is minimal in the LFP. The LFP is thus composed of the more sustained currents in the tissue, such as the [[synapse|synaptic]] and [[Somatology|somato]]-[[Dendrite|dendritic]] currents. Data-driven models have shown a predictive relationship between the LFPs and spike activity.<ref name="Michmizos 2012">{{cite journal|last=Michmizos|first=K|author2=Sakas, D |author3=Nikita, K |title=Prediction of the timing and the rhythm of the parkinsonian subthalamic nucleus neural spikes using the local field potentials.|journal=IEEE Transactions on Information Technology in Biomedicine|year=2012|volume=16|issue=2|pages=190–97|doi=10.1109/TITB.2011.2158549|pmid=21642043|s2cid=11537329}}</ref> The major slow currents involved in generating the LFP are believed to be the same that generate the [[postsynaptic potential]] (PSP). It was originally thought that [[Excitatory postsynaptic potential|EPSP]]s and [[Inhibitory postsynaptic potential|IPSP]]s were the exclusive constituents of LFPs, but phenomena unrelated to synaptic events were later found to contribute to the signal (Kobayashi 1997).<ref name="Kamondi 1998">{{cite journal|last=Kamondi|first=A|author2=Acsády, L |author3=Wang, XJ |author4= Buzsáki, G |title=Theta oscillations in somata and dendrites of hippocampal pyramidal cells in vivo: activity-dependent phase-precession of action potentials.|journal=Hippocampus|year=1998|volume=8|issue=3|pages=244–61|doi=10.1002/(SICI)1098-1063(1998)8:3<244::AID-HIPO7>3.0.CO;2-J|pmid=9662139|s2cid=10021185}}</ref>

Part of the [[low-pass filter]]ing giving rise to local field potentials is due to complex electrical properties of extracellular space.<ref name="Bédard 2004">{{cite journal|last=Bédard|first=C|author2=Kröger, H |author3=Destexhe, A |title=Modeling extracellular field potentials and the frequency-filtering properties of extracellular space.|journal=Biophysical Journal|date=Mar 2004|volume=86|issue=3|pages=1829–42|arxiv=physics/0303057 | doi=10.1016/S0006-3495(04)74250-2|pmid=14990509|pmc=1304017|bibcode=2004BpJ....86.1829B}}</ref> The fact that the extracellular space is not homogeneous, and composed of a complex aggregate of highly [[Electrical resistivity and conductivity|conductive]] fluids and low-conductive and [[capacitance|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.