SpikeMetrics

Computes quality metrics for sorted units. This module can calculate metrics separately for individual epochs. If no epochs are specified, metrics are computed for the entire recording.

The base code (and portions of the README images/description) was ported from: https://github.com/AllenInstitute/ecephys_spike_sorting/tree/master/ecephys_spike_sorting/modules/quality_metrics

Copyright © 2019. Allen Institute. All rights reserved.

Included Metrics

Metric	Icon	Description	Reference
Spike Count		Spike count in an epoch
Firing rate		Mean spike rate in an epoch
Presence ratio		Fraction of epoch in which spikes are present
ISI violations		Rate of refractory-period violations
Isolation distance		The Mahalanobis distance from a specified unit within as many spikes belong to the specified unit as to other units	Harris et al. Neuron 32.1 (2001): 141-149.
L-ratio		The Mahalanobis distance and χ2 inverse cdf (given the assumption that the spikes in the cluster distribute normally in each dimension) are used to find the probability of cluster membership for each spike.	Schmitzer-Torbert and Redish. J Neurophy 91.5 (2004): 2259-2272.
d'		The classification accuracy between units based on linear discriminant analysis (LDA).	Hill et al. (2011) J Neurosci 31, 8699-9705
Nearest-neighbors		Non-parametric estimate of unit contamination using nearest-neighbor classification.	Chung et al. (2017) Neuron 95, 1381-1394
Silhouette score		A standard metric for quantifying cluster overlap
Maximum drift		Maximum change in spike depth throughout recording
Cumulative drift		Cumulative change in spike depth throughout recording

A Note on Calculations

For metrics based on waveform principal components (isolation distance, L-ratio, d', and nearest neighbors hit rate and false alarm rate), it is typical to compute the metrics for all pairs of units and report the "worst-case" value. We have found that this tends to under- or over-estimate the degree of contamination when there are large firing rate differences between pairs of units that are being compared. Instead, we compute metrics by sub-selecting spikes from all other units on the same set of channels, which seems to give a more accurate picture of isolation quality. We would appreciate feedback on whether this approach makes sense.