How spurious correlations affect a correlation-based measure of spike timing reliability

The spike timing reliability of a neuron can be assessed via measuring the similarity of spike trains obtained in trials with repeated presentations of the same stimulus. Using a correlation-based measure of spike timing reliability we show that spurious correlations between independent Poisson spike trains can lead to a systematic misinterpretation to an extent that scales with the neural spike rate. Therefore, a correction is essential before comparing neurons with distinctly different spike rates. Such a comparison may, for instance, guide the choice of stimulus selective sensory neurons that are pooled for optimal stimulus reconstruction. We propose straightforward methods to abstract from these spurious correlations and demonstrate effects in an application to recorded spike trains of a retinal ganglion cell population.