Current Source Density (CSD) Analysis


Synonyms CSD, CSD method, reconstruction of current sources Definition Current Source Density analysis (CSD) is a class of methods of analysis of extracellular electric potentials recorded at multiple sites leading to estimates of current sources generating the measured potentials. It is usually applied to low-frequency part of the potential (called the Local Field Potential, LFP) and to simultaneous recordings or to recordings taken with fixed time reference to the onset of specific stimulus (Evoked Potentials, EP). Among the different mechanisms contributing to extracellular electric potential in the tissue (Buzsaki et al., 2012, Einevoll et al., 2012) transmembrane currents in neurons are believed to dominate. These are ionic currents passing through all the different membrane channels (passive, voltage-dependent, calcium-dependent, synaptic, etc.) as well as the capacitive currents which, while charging the membrane, also contribute to the motion of ions in the extracellular space, influencing the extracellular potential and seen by the extracellular electrode. The places where net current is entering or leaving the cell are called current sources or sinks. While these sources are localized along the membrane of the neuron, in practice, with a finite resolution afforded by available electrode setups and limited by typical densities, we may only recover coarse-grained density. This is what we have in mind when discussing estimation of Current Source Density. Figure 1 shows the relation between the " microscopic " currents (a), coarse-grained field we usually have in mind (b) and a reconstruction of the CSD from measured potentials. CSD analysis can be performed for signals in full spectrum or in any selected band, although it is usually applied to the Low Frequency Part (<500Hz) of the extracellular potential (LFP). We propose here such an expansion of LFP as the commonly used term Local Field Potential is actually a misnomer, since due to the long range nature of the electric field LFP can be observed millimeters away from sources (e. When net positive current enters the cell we speak of current sink and it corresponds to negative CSD. When net negative current enters the cell we speak of current source and it corresponds to positive CSD. Since negative CSD is observed for excitatory synaptic stimulation (positive current entering the cell / negative CSD), many researchers prefer to denote current sinks by red (" hot spot ") and current sources by blue. There is a comparable number of researchers who prefer to do the opposite, …

DOI: 10.1007/978-1-4614-7320-6_544-1

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