How does the grid scale support accurate spatial memory and navigation?

Abstract

How does the grid scale support accurate spatial memory and navigation? This critical piece of the puzzle is currently missing from experimental work on grid cells. Previous research has demonstrated that the medial entorhinal cortex (MEC) is required for accurate spatial memory and navigation. But few studies have examined the importance of grid scale in these same processes. Here, we examine how the topographical organization of grid scale contributes to spatial memory and navigation by using behavioral pradigms combined with optogenetic manipulations. Multiple tasks were utilized; object exploration, the Barnes maze and a spatial delay non-match-to sample task in an 8-arm radial maze. We hypothesize that optogenetic photoinhibition of the smallest grid scale will reduce spatial accuracy, resulting in mice showing impairments when asked to discriminate between spatial locations at a fine spatial resolution. The results indicate that the dorsalmost MEC is crucial for spatial memory and navigation, and might be especially impotant for recognizing and relating to a novel spatial change in the evironment. We also demonstrate behavioral experimental designs that may be used in further experimentation with optogenetics.