Lateral entorhinal neurons are not spatially selective in cue‐rich environments

Abstract

The hippocampus is a brain region that is critical for spatial learning, context-dependent memory, and episodic memory. It receives major inputs from the medial entorhinal cortex (MEC) and the lateral entorhinal cortex (LEC). MEC neurons show much greater spatial firing than LEC neurons in a recording chamber with a single, salient landmark. The MEC cells are thought to derive their spatial tuning through path integration, which permits spatially selective firing in such a cuedeprived environment. In accordance with theories that postulate two spatial mapping systems that provide input to the hippocampus-an internal, path-integration system and an external, landmarkbased system-it was possible that LEC neurons can also convey a spatial signal, but that the signal requires multiple landmarks to define locations, rather than movement integration. To test this hypothesis, neurons from the MEC and LEC were recorded as rats foraged for food in cuerich environments. In both environments, LEC neurons showed little spatial specificity, whereas many MEC neurons showed a robust spatial signal. These data strongly support the notion that the MEC and LEC convey fundamentally different types of information to the hippocampus, in terms of their spatial firing characteristics, under various environmental and behavioral conditions.

Functional correlates of the lateral and medial entorhinal cortex: objects, path integration and local–global reference frames

“…This difference in connectivity is mirrored by different properties of place cells along the CA1 transverse axis. Neurons in the MEC-recipient, proximal CA1 have higher spatial specificity and stronger theta modulation than neurons in the LECrecipient, distal CA1 [18], consistent with known physiological differences between the LEC and MEC [19][20][21], as discussed below. Based on such anatomical considerations, investigators in the 1990s began to consider that the entorhinal cortex formed two distinct, functional processing streams into the hippocampus [5][6][7][8][22][23][24][25].…”

“…Other cells fire like place cells in locations where the animal never experienced an object, but apparently only when individual objects are present in the environment [35]. Textures on the surface of a track or salient landmarks outside the apparatus are unable to support spatial firing [20] (although a weak spatial signal can be detected when local and global cues are placed in conflict, as described above [50]). Because LEC cells with spatial properties are rare and few studies of LEC have been performed in freely moving animals, we know very little about the properties of these cells and the cues that drive their firing.…”

Spatial and Nonspatial Representations in the Lateral Entorhinal Cortex

“…(b) Even in complex environments with multiple landmarks, LEC neurons did not show spatial selectivity in the large box (135 Â 135 cm) or circular track (56 cm inner diameter, 76 cm outer diameter). In contrast, MEC neurons showed spatial selectivity (Yoganarasimha et al 2011). Notice the multiple peaks in the three MEC neurons are nonrandomly distributed, forming tessellating arrays of equilateral triangles.…”

How Does the Brain Solve the Computational Problems of Spatial Navigation?

“…Moreover, the spatial periodicity of 1D responses appears to be much larger than the periods seen in 2D. These observations raise the question of whether the 1D response is generated under the same dynamical mechanisms as the 2D response (e.g., whether the 1D response is simply a 1D slice through a regular 2D grid (Yoganarasimha et al (2011);Domnisoru et al (2013) and unpublished observations by KJ Yoon, S Lewallen, A Kinkhabwalla, DW Tank, and IR Fiete), or whether 1D dynamics, and by extension, the grid cell code in 1D environments, is in a distinct dynamical regime and follows very different rules).…”