Place Cells are Clustered by Field Location in CA1 Hippocampus

Both modern and historic neuroscience have been challenged by achieving an understanding of neuron cir-cuits, and determining the computational and organizational principles underlying these circuits. Deeper un-derstanding of the organization of brain circuits and cell types, including in the hippocampus, is required for neuroscience advances and understanding governing principles of the brain. In this manuscript, we pioneer a new mathematical method to analyze the spatial clustering of active neurons in the hippocampus. We use cal-cium imaging and a rewarded navigation task to record from 1000s of place cells in the CA1 of freely moving rats. We then use statistical techniques in widespread use in geographic mapping studies, global Moran’s I and local Moran’s I, to demonstrate that cells that code for similar spatial locations tend to form small spatial clusters. We show that these clusters are primarily formed by cells that have place fields around previously rewarded locations. That said, there is no obvious topographic mapping of environmental location onto the hippocampus. Insights into hippocampal organization, as in this study, can elucidate mechanisms underlying motivational behaviors, spatial navigation, and memory formation.