How do spike collisions affect spike sorting performance?

Abstract

Recently, a new generation of devices have been developed to record neural activity simultaneously from hundreds of electrodes with a very high spatial density, both for in vitro and in vivo applications. While these advances enable to record from many more cells, they also challenge the already complicated process of spike sorting (i.e. extracting isolated single-neuron activity from extracellular signals). In this work, we used synthetic ground-truth recordings with controlled levels of correlations among neurons to quantitatively benchmark the performance of state-of-the-art spike sorters focusing specifically on spike collisions. Our results show that while modern template-matching based algorithms are more accurate than density-based approaches, all methods, to some extent, failed to detect synchronous spike events of neurons with similar extracellular signals. Interestingly, the performance of the sorters is not largely affected by the the spiking activity in the recordings, with respect to average firing rates and spike-train correlation levels. Since the performances of all modern spike sorting algorithms can be affected as function of the activity of the recorded neurons, scientific claims on correlations and synchrony should be carefully assessed based on the analysis provided in this paper.

Significance statement

High-density extracellular recordings allow experimentalists to get access to the spiking activity of large neuronal population, via the procedure of spike sorting. It is widely known that spike sorters are affected by spike collisions, i.e., the occurrence of spatio-temporally overlapping events, but a quantitative benchmark is still lacking. In this contribution, we perform systematic comparisons on the performance of many different spike sorters against spike collisions, showing that modern spike sorters, to different degrees, are still affected by synchronous events. Our results suggest that scientific claims on neuron correlations and synchrony should be carefully assessed as they could result from spike sorting errors.