Grid cells in medial entorhinal cortex (MEC) can be modeled using oscillatory interference or attractor dynamic mechanisms that perform path integration, a computation requiring information about running direction and speed. The two classes of computational models often use either an oscillatory frequency or a firing rate that increases as a function of running speed. Yet it is currently not known whether these are two manifestations of the same speed signal or dissociable signals with potentially different anatomical substrates. We examined coding of running speed in MEC and identified these two speed signals to be independent of each other within individual neurons. The medial septum (MS) is strongly linked to locomotor behavior and removal of MS input resulted in strengthening of the firing rate speed signal, while decreasing the strength of the oscillatory speed signal. Thus two speed signals are present in MEC that are differentially affected by disrupted MS input.

The retrosplenial cortex is reciprocally connected with multiple structures implicated in spatial cognition, and damage to the region itself produces numerous spatial impairments. Here, we sought to characterize spatial correlates of neurons within the region during free exploration in two-dimensional environments. We report that a large percentage of retrosplenial cortex neurons have spatial receptive fields that are active when environmental boundaries are positioned at a specific orientation and distance relative to the animal itself. We demonstrate that this vector-based location signal is encoded in egocentric coordinates, is localized to the dysgranular retrosplenial subregion, is independent of self-motion, and is context invariant. Further, we identify a subpopulation of neurons with this response property that are synchronized with the hippocampal theta oscillation. Accordingly, the current work identifies a robust egocentric spatial code in retrosplenial cortex that can facilitate spatial coordinate system transformations and support the anchoring, generation, and utilization of allocentric representations.

Theta (6-12 Hz) field potentials and the synchronization (coherence) of these potentials present neural network indices of hippocampal physiology. Theta signals within the hippocampal formation may reflect alterations in sensorimotor integration, the flow of sensory input, and/or distinct cognitive operations. While the power and coherence of theta signals vary across lamina within the septal hippocampus, limited information is available about variation in these indices across the septotemporal (long) or areal axis. The present study examined the relationship of locomotor speed to theta indices at CA1 and dentate gyrus (DG) sites across the septotemporal axis as well as in the entorhinal cortex. Our findings demonstrate the dominant relationship of speed to theta indices at septal sites. This relationship diminished systematically with distance from the septal pole of the hippocampus at both CA1 and DG sites. While theta power at entorhinal sites varied in relation to speed, there were no differences across the areal axis of the entorhinal cortex. Locomotor speed was also related to changes in theta coherence along the septotemporal axis as well as between the hippocampus and entorhinal cortex. In addition to the speed-related variation, we observed a decrease in theta power at more temporal hippocampal sites over repeated behavioral testing within a single day that was not observed at septal sites. The results outline a dynamic and distributed pattern of network activity across the septotemporal axis of the hippocampus in relation to locomotor speed and recent past experience.

31The retrosplenial cortex is reciprocally connected with a majority of structures implicated in 32 spatial cognition and damage to the region itself produces numerous spatial impairments. 33However, in many ways the retrosplenial cortex remains understudied. Here, we sought to 34 characterize spatial correlates of neurons within the region during free exploration in two-35 dimensional environments. We report that a large percentage of retrosplenial cortex neurons 36 have spatial receptive fields that are active when environmental boundaries are positioned at a 37 specific orientation and distance relative to the animal itself. We demonstrate that this vector-38 based location signal is encoded in egocentric coordinates, localized to the dysgranular 39 retrosplenial sub-region, independent of self-motion, and context invariant. Further, we identify a 40 sub-population of neurons with this response property that are synchronized with the 41 hippocampal theta oscillation. Accordingly, the current work identifies a robust egocentric spatial 42 code in retrosplenial cortex that can facilitate spatial coordinate system transformations and 43 support the anchoring, generation, and utilization of allocentric representations. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 108 From a connectivity standpoint, the retrosplenial cortex (RSC) is an excellent candidate to 109 examine egocentric representations during navigation. Further, theoretical work has posited that 110 RSC forms a computational hub for supporting coordinate transformations (Byrne et al., 2007;111 Clark et al., 2018; Rounds et al., 2018; Bicankski and Burgess, 2018). RSC is composed of two 112 interconnected sub-regions, dysgranular (dRSC) and granular (gRSC), which have slightly 113 different connectivity with cortical and subcortical regions (Shibata et al., 2009). dRSC (in mice 114 agranular RSC) is positioned along the dorsal surface of the brain and possesses biased 115 interconnectivity with association, sensory, and motor processing regions that code in 116

Movement through space is a fundamental behavior for all animals. Cognitive maps of environments are encoded in the hippocampal formation in an allocentric reference frame, but motor movements that comprise physical navigation are represented within an egocentric reference frame. Allocentric navigational plans must be converted to an egocentric reference frame prior to implementation as overt behavior. Here we describe an egocentric spatial representation of environmental boundaries in the dorsomedial striatum.