Quantitative measures of cluster quality for use in extracellular recordings

N. Schmitzer-Torbert, J. Jackson, D. Henze, K. Harris, A. D. Redish

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While the use of multi-channel electrodes (stereotrodes and tetrodes) has allowed for the simultaneous recording and identification of many neurons, quantitative measures of the quality of neurons in such recordings are lacking. In multi-channel recordings, each spike waveform is discriminated in a high-dimensional space, making traditional measures of unit quality inapplicable. We describe two measures of unit isolation quality, L ratio and Isolation Distance, and evaluate their performance using simulations and tetrode recordings. Both measures quantified how well separated the spikes of one cluster (putative neuron) were from other spikes recorded simultaneously on the same multi-channel electrode. In simulations and tetrode recordings, both Lratio and Isolation Distance discriminated well- and poorly-separated clusters. In data sets from the rodent hippocampus in which neurons were simultaneously recorded intracellularly and extracellularly, values of Isolation Distance and Lratio were related to the correct identification of spikes.

Original languageEnglish (US)
Pages (from-to)1-11
Number of pages11
Issue number1
StatePublished - 2005

Bibliographical note

Funding Information:
We would like to thank G. Buzsaki for generously supplying the simultaneous intracellular/extracellular hippocampal data. We would also like to thank Matthew Wiener for helpful comments on an earlier draft of this manuscript. This work was partially supported by NSF-IGERT 9870633 (N.C.S.-T., J.C.J.), by an NSF fellowship to N.C.S.-T. by NIH MH68029 (A.D.R., J.C.J.) and by NIH MH73245 (K.D.H.).


  • extracellular recording
  • multi-channel electrode
  • spike sorting
  • stereotrode
  • tetrode
  • unit isolation


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