Impact of multiunit merging on neural information encoding.
<p>Multiunit merging, a common artifact in spike sorting, combines spikes from multiple neurons into a single “putative neuron.” This inflates firing rates—particularly masking low firing rate neurons—and obscures their distinct information-encoding properties. <b>(A)</b> Schematic...
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2025
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| Riassunto: | <p>Multiunit merging, a common artifact in spike sorting, combines spikes from multiple neurons into a single “putative neuron.” This inflates firing rates—particularly masking low firing rate neurons—and obscures their distinct information-encoding properties. <b>(A)</b> Schematic illustrating how merged activity from two true neurons can appear task-irrelevant, as the combined firing pattern shows little difference between two task conditions (green and orange vs. purple). Proper sorting reveals that each neuron encodes unique information. <b>(B)</b> Time Interval Comparison Task (TICT). Monkeys compare two intervals (Int1 and Int2) separated by a 2-second delay, then press one of two buttons to indicate which interval was longer. Int1 (400 to 2000 ms) is shown in shades of blue. Data was recorded in dorsal prefrontal cortex (DPC, shown in brain cartoon). <b>(C)</b> Top: Raster plot of a misclassified multiunit in the DPC, aligned to the end of (<i>t</i> = 0 = start of the delay). Gray rectangles indicate Int1 backpropagated from <i>t</i> = 0. Black ticks indicate spikes during correct trials; red ticks indicate spikes during error trials. Bottom: The average firing rate and mutual information fail to show meaningful encoding. <b>(D)</b> The first neuron contributes to the multiunit (panel C). Despite a low firing rate, it exhibits a clear positive encoding of Int1 (larger stimulus intensities produce higher firing rates). <b>(E)</b> The second neuron shows a strong early sensory response followed by a negative encoding of Int1. Merging these two distinct patterns masks each neuron’s specific role in information processing. The multiunit and UMAP sorted neuronal activity used to generate the raster plots and firing rates is publicly available at [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.3003527#pbio.3003527.ref043" target="_blank">43</a>], and the code to compute firing rates and mutual information is available at [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.3003527#pbio.3003527.ref049" target="_blank">49</a>].</p> |
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