Medial entorhinal spike clusters carry more finely tuned spatial information than single spikes

Abstract

Many cells within the entorhinal cortex (EC) fire relatively infrequently, with the majority of their spikes separated by many hundreds of milliseconds. However, most cells are seen to occasionally fire two, three, or more spikes in quick succession. Recent evidence has shown that, in EC grid cells, "burstier" cells; cells that fire more of their spikes in bursts, have more well defined spatial characteristics than cells that fire fewer bursts. However, there is evidence that the window for considering related spikes in MEC could be as long as 100ms. Here, we divide the spikes fired by single cells into single spikes and "clusters" of spikes occuring within 100ms. We show that these burst "clusters" of spikes fired by cells in MEC convey more finely tuned spatial and directional information than the numerically more common single spikes. In addition, we find that introducing environmental uncertainty decreases the ratio of clusters fired to single spikes. Most crucially, we find that although single spikes are less spatially precise than clusters, they are more temporally precise - these spikes are more closely entrained to LFP theta than clusters. These findings demonstrate that clusters of spikes in EC convey more specific information about space than single spikes, may reflect "certainty" about spatial position and direction, and may represent a different firing "mode" in which intraregional communication is less relevant than interregional traffic.