Dentate spikes comprise a continuum of relative input strength from the lateral and medial entorhinal cortex.

Abstract

Hippocampal dentate spikes (DS) are synchronous population events generated in the dentate gyrus thought to support memory processing. DS are classified into type 1 (DS1) and type 2 (DS2) based on current sinks in the outer or middle molecular layer, where the axons of the lateral or medial entorhinal cortex terminate, respectively. This widely used classification method constrains DS into a bimodal distribution without properly testing whether such constraint is appropriate. Here we utilized silicon probe recordings with high spatial resolution spanning all layers of the dentate gyrus and discovered that the contribution of LEC/MEC inputs to DS follows a continuous distribution. We introduce a third type (DS3) that captures a previously unreported component of the distribution: simultaneous current sinks in the outer/middle molecular layer, suggestive of synchronized activation from the LEC/MEC which could facilitate binding. We verify DS3 in several data sets from independent laboratories and characterize their brain state dependence and neural recruitment.