spike sorting for extracellular recordings kenneth d. harris rutgers university
TRANSCRIPT
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Spike Sorting for Extracellular Recordings
Kenneth D. HarrisRutgers University
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Aims
We would like to …
Monitor the activity of large numbers of neurons simultaneously
Know which neuron fired when Know which neuron is of which type Estimate our errors
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Extracellular Recording Hardware
You can buy two types of hardware, allowing
Wide-band continuous recordings
Filtered, spike-triggered recordings
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The Tetrode Four microwires twisted into a
bundle Different neurons will have
different amplitudes on the four wires
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Raw Data
Spikes
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High Pass Filtering Local field potential is primarily at
low frequencies.
Spikes are at higher frequencies.
So use a high pass filter. 800hz cutoff is good.
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Filtered Data
Cell 1
Cell 2
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Spike Detection Locate spikes at times of
maximum extracellular negativity
Exact alignment is important: is it on peak of largest channel or summed channels?
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Data Reduction We now have a waveform for each
spike, for each channel.
Still too much information!
Before assigning individual spikes to cells, we must reduce further.
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Principal Component Analysis Create “feature vector” for each spike.
Typically takes first 3 PCs for each channel.
Do you use canonical principal components, or new ones for each file?
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“Feature Space”
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Cluster Cutting Which spikes belong to which
neuron?
Assume a single cluster of spikes in feature space corresponds to a single cell
Automatic or manual clustering?
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Cluster Cutting Methods Purely manual – time consuming,
leads to high error rates.
Purely automatic – untrustworthy.
Hybrid – less time consuming, lowest error rates.
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Semi-automatic Clustering
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Cluster Quality Measures Would like to automatically detect
which cells are well isolated.
Will define two measures.
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Isolation Distance
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L_ratio
21ratio clusternoise
L cdf N
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False Positives and Negatives
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Room for Improvement? Improved alignment methods, leading
to nicer clusters.
Faster automatic sorting.
Better human-machine interaction.
Fully automatic sorting.