Local field potential

Summary

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,

Official source

https://en.wikipedia.org/wiki/Local_field_potential

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Cell-type- and activity-dependent extracellular correlates of intracellular spiking

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Despite decades of extracellular action potential (EAP) recordings monitoring brain activity, the biophysical origin and inherent variability of these signals remains enigmatic. We performed whole-cell patch recordings of excitatory and inhibitory neurons in rat somatosensory cortex slice while positioning a silicon probe in their vicinity to concurrently record intra- and extracellular voltages for spike frequencies under 20 Hz. We characterize biophysical events and properties (intracellular spiking, extracellular resistivity, temporal jitter, etc.) related to EAP-recordings at the single-neuron level in a layer-specific manner. EAP-amplitude was found to decay as the inverse of distance between the soma and the recording electrode with similar (but not identical) resistivity across layers. Furthermore, we assessed a number of EAP-features and their variability with spike activity: amplitude (but not temporal) features varied substantially (approx. 30-50% compared to mean) and non-monotonically as a function of spike frequency and spike order. Such EAP-variation only partly reflects intracellular somatic spike variability and points to the plethora of processes contributing to the EAP. Also, we show that the shape of the EAP-waveform is qualitative similar to the negative of the temporal derivative to the intracellular somatic voltage - as expected from theory. Finally, we tested to what extent EAPs can impact the lowpass filtered part of extracellular recordings, the local field potential (LFP), typically associated with synaptic activity. We found that spiking of excitatory neurons can significantly impact the LFP at frequencies as low as 20 Hz. Our results question the common assertion that LFPs act as proxy for synaptic activity.

American Physiological Society2015

A Biophysically Detailed Model of Neocortical Local Field Potentials Predicts the Critical Role of Active Membrane Currents

Sean Lewis Hill, Henry Markram, Rodrigo de Campos Perin, Michael Reimann

Brain activity generates extracellular voltage fluctuations recorded as local field potentials (LFPs). It is known that the relevant microvariables, the ionic currents across membranes, jointly generate the macrovariables, the extracellular voltage, but neither the detailed biophysical knowledge nor the required computational power have been available to model these processes. We simulated the LFP in a model of the rodent neocortical column composed of >12,000 reconstructed, multicompartmental, and spiking cortical layer 4 and 5 pyramidal neurons and basket cells, including five million dendritic and somatic compartments with voltage- and ion-dependent currents, realistic connectivity, and probabilistic AMPA, NMDA, and GABA synapses. We found that, depending on a number of factors, the LFP reflects local and cross-layer processing. Active currents dominate the generation of LFPs, not synaptic ones. Spike-related currents impact the LFP not only at higher frequencies but below 50 Hz. This work calls for re-evaluating the genesis of LFPs.

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Band offsets of lattice-matched semiconductor heterojunctions through hybrid functionals and G(0)W(0)

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To assess the accuracy of hybrid functional and many-body GW methods, we study the band offsets for a set of lattice-matched semiconductor heterojunctions, including AlAs/GaAs(100), AlP/GaP(100), Si/GaP(110), Ge/GaAs(110), Ge/AlAs(110), Ge/ZnSe(110), and ZnSe/GaAs(110). The band-edge positions are first obtained for the bulk semiconductors and then aligned through the lineup of a local reference potential at the interface. The band-edge positions critically depend on the electronic-structure method, while the interface dipole is already well accounted for with semilocal density functionals. The two advanced electronic-structure schemes yield consistent valence-band offsets in close agreement with experiment, slightly improving upon semilocal functionals. At variance, conduction-band offsets are subject to larger deviations and improve with the accuracy of the calculated band gaps. In case one is willing to take band gaps from experiment, the best description of the band alignment for the present heterojunctions is achieved by relying on the calculated valence band offsets rather than on hybrid functionals in which the exchange mixing parameter is adjusted.

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