Local field potential: Difference between revisions

'''Local field potentials''' ('''LFP''') are transient electrical signals generated in nervous[[nerve]]s 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 a 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 be recorded, for example, via a microelectrode placed in the [[brain]] of ana anesthetizedhuman<ref>{{cite journal | vauthors = Peyrache A, Dehghani N, Eskandar EN, Madsen JR, Anderson WS, Donoghue JA, Hochberg LR, Halgren E, Cash SS, Destexhe A | display-authors = 6 | title = Spatiotemporal dynamics of neocortical excitation and inhibition during human sleep | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 109 | issue = 5 | pages = 1731–1736 | date = January 2012 | pmid = 22307639 | pmc = 3277175 | doi = 10.1073/pnas.1109895109 | doi-access = free | bibcode = 2012PNAS..109.1731P }}</ref> or animal subject, or in an [[in vitro]] brain [[Slice preparation|thin slice]].

During local field potential recordings, a signal is recorded using an [[extracellular]] [[microelectrode]] placed sufficiently far from individual local [[neurons]] to prevent any particular [[cell (biology)|cell]] from dominating the electrophysiological signal. This signal is then [[low-pass filter]]ed, cut off at ~300 [[Hertz|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. The unfiltered signal reflects the sum of action potentials from cells within approximately 50-350 μm from the tip of the electrode<ref name="Legatt 1980">{{cite journal |last vauthors = Legatt|first= AD, |author2=Arezzo, J, |author3=Vaughan HG, Jr| title = Averaged multiple unit activity as an estimate of phasic changes in local neuronal activity: effects of volume-conducted potentials. | journal = Journal of Neuroscience Methods|date=Apr 1980| volume = 2 | issue = 2 | pages =203–17 203–217 | date = April 1980 | pmid = 6771471 | doi = 10.1016/0165-0270(80)90061-8 |pmid s2cid =6771471 32510261 }}</ref><ref name="Gray 1995">{{cite journal |last vauthors = Gray|first= CM|author2=Maldonado, Maldonado PE, |author3=Wilson, M |author4=, McNaughton, B | title = Tetrodes markedly improve the reliability and yield of multiple single-unit isolation from multi-unit recordings in cat striate cortex. | journal = Journal of Neuroscience Methods|date=Dec 1995| volume = 63 | issue =1-2 1–2 | pages = 43–54 | date = December 1995 | pmid = 8788047 | doi = 10.1016/0165-0270(95)00085-2 |pmid s2cid =8788047 3817420 }}</ref> and slower ionic events from within 0.5–3&nbsp;mm from the tip of the electrode.<ref name="Juergens 1999">{{cite journal |last vauthors = Juergens|first= E|author2=Guettler, Guettler A, |author3=Eckhorn, R | title = Visual stimulation elicits locked and induced gamma oscillations in monkey intracortical- and EEG-potentials, but not in human EEG. | journal = Experimental Brain Research|date=Nov 1999| volume = 129 | issue = 2 | pages =247–59 247–259 | date = November 1999 | pmid = 10591899 | doi = 10.1007/s002210050895 |pmid s2cid =10591899 25265991 }}</ref> The low-pass filter removes the [[Voltage spike|spike]] component of the signal and passes the lower [[frequency]] signal, the LFP.

The voltmeter or analog-to-digital converter to which the microelectrode is connected measures the [[electrical potential difference]] (measured in [[volts]]) between the microelectrode and a reference electrode. One end of the reference electrode is also connected to the voltmeter while the other end is placed in a medium which is continuous with, and compositionally identical to the extracellular medium. 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]]. This is due to the random movement of ions in the medium and electrons in the electrode. However, when placeplaced in [[neural tissue]] the opening of an ion channel results in the net flow of ions into the cell from the extracellular medium, or out of the cell into the extracellular medium. These local currents result in larger changes in the electrical potential between the local extracellular medium and the interior of the recording electrode. The overall recorded signal thus represents the potential caused by the sum of all local currents on the surface of the electrode.

The local field potential is believed to represent the [[neuralsum oscillation|synchronisedof input]]synaptic inputs into the observed area, as opposed to the [[Action potential|spikespikes]] 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, suchthat asare thegenerated by synaptic activity ([[synapseExcitatory postsynaptic potential|synapticEPSC]]s and [[SomatologyInhibitory postsynaptic potential|somatoIPSC]]s).<ref name="Kamondi 1998">{{cite journal | vauthors = Kamondi A, Acsády L, Wang XJ, Buzsáki G | title = Theta oscillations in somata and dendrites of hippocampal pyramidal cells in vivo: activity-[[Dendritedependent phase-precession of action potentials |dendritic]] currentsjournal = Hippocampus | volume = 8 | issue = 3 | pages = 244–261 | year = 1998 | pmid = 9662139 | doi = 10.1002/(SICI)1098-1063(1998)8:3<244::AID-HIPO7>3.0.CO;2-J | s2cid = 10021185 | doi-access = free }}</ref> Data-driven models have shown a predictive relationship between the LFPs and spike activity.<ref name="Michmizos 2012">{{cite journal |last vauthors = Michmizos|first=K|author2=Sakas KP, Sakas D, |author3=Nikita, KKS | 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 =190–97 190–197 | date = March 2012 | pmid = 21642043 | doi = 10.1109/TITB.2011.2158549 | s2cid = 11537329 }}</ref> TheA majorcommon slowmethod currentsto involved in generating theinvestigate LFP areoscillations believedthat lead to bespikes theis sameto thatcalculate generatespike-triggered theaverages [[postsynaptic(see potential]] (PSPfigure). ItThis wasis originallydone thoughtafter thatthe [[Excitatoryrecording postsynaptic(off potential|EPSP]]sline) andby [[Inhibitorydetecting postsynapticthe potential|IPSP]]sspikes wereas thefast exclusivedownward constituentsdeflections, ofcutting LFPs,out butthe phenomenatemporal unrelatedsections toaround synapticthe eventsspike were(+/- later250 foundms) toand contribute toaveraging the signalspike-aligned (Kobayashitraces 1997)for each recording site.<ref name="Kamondi:0" 1998"/>{{cite journal|last=Kamondi|first=A|author2=AcsádyAlternatively, Lspikes |author3=Wang,can XJbe |author4=removed Buzsáki,from Gthe |title=Thetaextracellular oscillationsrecording intraces somataby and dendrites of hippocampal pyramidal cells in vivo: activitylow-dependentpass phase-precessionfiltering, ofrevealing actionthe potentialsLFP.|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}}</ref>

Which cells contribute to the slow field variations is determined by the geometric configuration of the cells themselves. In some cells, the dendrites face one direction and the [[Soma (biology)|soma]] another, such as the [[pyramidal cells]]. This is known as an open field geometrical arrangement. When there is simultaneous activation of the dendrites a strong [[dipole]] is produced. In cells where the [[dendrites]] are arranged more [[radius|radial]]ly, the potential difference between individual dendrites and the soma tend to cancel out with diametrically opposite dendrites, this configuration is called a closed field geometrical arrangement. As a result the net potential difference over the whole cell when the dendrites are simultaneously activated tends to be very small. Thus changes in the local field potential represent simultaneous dendritic events in cells in the open field configuration.

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 vauthors = Bédard|first= C|author2=Kröger, 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 1829–1842 | date = March 2004 | pmid = 14990509 | pmc = 1304017 | doi = 10.1016/S0006-3495(04)74250-2 |pmid arxiv =14990509 physics/0303057 |pmc bibcode =1304017 2004BpJ....86.1829B }}</ref> The fact that the extracellular space is not homogeneous, and is 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.

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