Cross-correlation artifacts induced by failure of clustering method for temporally overlapping spikes.

<p>(<b>A</b>) The cross-correlation function (CCF), which expresses the firing rate of one neuron relative to the spike times of another neuron. The CCF shows a substantial elevation in the firing of the primary cell in a time window extending roughly ± 5 ms around the spike of the secondary cell, as well as a sharp notch at the origin (width roughly ± 1 ms). The timescale of this notch matches the range of times over which the waveforms interfere with each other, as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062123#pone-0062123-g001" target="_blank">Figure 1</a>. (<b>B</b>) Summary of pairwise cross-correlations for all adjacent ON retinal ganglion cells within a simultaneously recorded population (338 pairs). Each row of the image represents the CCF between a pair of cells (shade of grey represents firing rate relative to the mean). Rows are sorted according to the value of the center time bin. (<b>C</b>) For pairs of neurons with significant synchronized firing, the magnitude of the secondary spike waveform (corresponding to the length of the red vector in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062123#pone-0062123-g001" target="_blank">Figure 1</a> ) provides a strong prediction of the strength of the CCF artifact (). We quantify the strength of the CCF artifact (index on vertical axis) as the difference between the average firing rate during the intervals of ms and ms, divided by the baseline firing rate.