Spike Sorting¶
Spike sorting is a combined detection and classification task for transient patterns in time series. In neuroscience this task is found when analysing voltage traces recorded from the brain of mammals. This kind of recording yields discrete time series that represent the brain activity of the cortex at the site under consideration.
Single cells in the cortex (neurons) communicate by means of electrical and chemical signals. These signals are called action potential (AP), and arise when a neuron receive enough input signals from other neurons. The AP builds as an ion current inside the cell body (soma) of the neuron. At certain threshold levels the current flows out of the soma and is released into a transmission channel (axon). At terminal points on the axon chemical transmission devices (sysnapses) communicate the AP to other neurons, in turn exciting ot inhibiting their activity. The ion current gives rise to a transmembrane potential as ion are transported from one side of the membrane to the other. This (de-) polarisation is measurable inside the neuron and in the medium surrounding the neuron. The time course of the membrane potential during an AP, as measured in the voltage trace recorded, has a very distinct gestalt, motivating the term spike.
The aim of the spike sorting task is to identify the points in time when an AP has occurred in the signal (spike detection) and to predict which of the neurons present has emitted this spike (spike sorting).
Todo
might need references
Intracellular Recordings¶
Voltage recordings from the inside of the neuron are called intracellular recordings. This kind of recording can help to understand intracellular current dynamics. In general the detection of the AP from intracellular recordings does not pose a challenge, so that this kind of recording will not be considered in detail here.
Todo
might need references
Extracellular recording¶
The leading paradigm to record ensembles of neurons from the cortex is that of extracellular recording. An electrode will be placed in the part of the cortex under consideration and record from the local neuronal population.
Cartoon of the experimental setup for extracellular recordings.
Literature Introduction¶
For further information about spike sorting please refer to the following publications [Lewiki99], [ScholarpediaSS] and more recent and recommended [Einevoll11].
Bayes Optimal Template Matching¶
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