CV2 Analysis

CV2 Analysis evaluates variability of interspike intervals by comparing only adjacent interspike intervals. CV2 statistic is less sensitive to rate variations than other measures such as the coefficient of variation of interspike intervals.

Parameters

Parameter	Description
Time Min (sec)	Only the timestamps in time interval [Time Min, Time Max] will be selected for analysis.
Time Max (sec)	Only the timestamps in time interval [Time Min, Time Max] will be selected for analysis.
Max Mean of ISI Pair (sec)	CV2 graph shows ISI variability versus Mean of ISI Pair. Max Mean of ISI Pair specifies maximum of X axis in CV2 graph
Mean of ISI Pair Bin (sec)	Bin size for calculation of CV2 mean and Standard Error of Mean.
Dot Size (pts)	Specifies the size of the dots shown at (Mean of ISI Pair, CV2) coordinates.

Summary of Numerical Results

The following information is available in the Summary of Numerical Results

Column	Description
Variable	Variable name.
CV2 Min	Y axis minimum.
CV2 Max	Y axis maximum.
Time Min	Minimum of the time interval that was used to select spikes
Time Max	Minimum of the time interval that was used to select spikes
CV2 Mean	Average of all CV2 values.
Spikes	The number of spikes used in calculation.
Mean Firing Rate	Mean firing rate of the spikes used in analysis.

Algorithm

If the spikes in a train occur at times t[i] (i = 1, 2, ..., N) then the ISIs will be

isi[i] = t[i] - t[i-1] (i = 2, 3, ..., N)

CV2 is then calculated as

CV2[i] = 2*abs(isi[i+1] - isi[i]) / (isi[i+1] - isi[i])

Dots in CV2 graph are drawn at (X,Y) locations (ISIPairMean[i], CV2[i]) where

ISIPairMean[i] = (isi[i+1] - isi[i]) / 2

X (ISI pair mean) axis is divided into bins. For each bin, the mean of CV2 values and the Standard Error of Mean of CV2 values are calculated.

Reference

Holt, Gary R., William R. Softky, Christof Koch, and Rodney J. Douglas. “Comparison of discharge variability in vitro and in vivo in cat visual cortex neurons.” Journal of Neurophysiology 75, no. 5 (1996): 1806-1814.