Representation of Non-Spatial and Spatial Information in the Lateral Entorhinal Cortex

Abstract

Some theories of memory propose that the hippocampus integrates the individual items and events of experience within a contextual or spatial framework. The hippocampus receives cortical input from two major pathways: the medial entorhinal cortex (MEC) and the lateral entorhinal cortex (LEC). During exploration in an open field, the firing fields of MEC grid cells form a periodically repeating, triangular array. In contrast, LEC neurons show little spatial selectivity, and it has been proposed that the LEC may provide non-spatial input to the hippocampus. Here, we recorded MEC and LEC neurons while rats explored an open field that contained discrete objects. LEC cells fired selectively at locations relative to the objects, whereas MEC cells were weakly influenced by the objects. These results provide the first direct demonstration of a double dissociation between LEC and MEC inputs to the hippocampus under conditions of exploration typically used to study hippocampal place cells.

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

“…As mentioned earlier, LEC cells are active when the rat investigates individual objects in an environment [35], and a small fraction of the cells fire at locations from which an object has been moved [35,44]. 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].…”

“…As mentioned earlier, LEC cells are active when the rat investigates individual objects in an environment [35], and a small fraction of the cells fire at locations from which an object has been moved [35,44]. 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]).…”

“…In parallel, the LEC was shown to be mostly devoid of spatially tuned neurons, at least in standard tasks in which there were prominent distal landmarks but few prominent, local landmarks [19]. By contrast, when local objects were introduced into the arena, a substantial proportion of superficial LEC neurons were active when the rat investigated the objects, whereas few superficial MEC neurons were affected by the objects [35].…”

“…The notion of a hierarchical, one-way processing loop, while convenient for creating conceptual models and organizing complex data into theoretical frameworks, is far removed from how the brain is truly organized. Although the place-like firing [35] and object-location memory responses [35,44] in LEC can be found in the hippocampusprojecting superficial layers, even these layers are presumably subjected to feedback from the hippocampus (similar to that shown for the MEC [48]) owing to cross-laminar connectivity and dendritic arborizations. Does it still make sense, then, to refer to these pathways as separate processing streams?…”

“…Physiologically, one synapse upstream from the entorhinal cortex, Furtak et al [40] showed that single units in the postrhinal cortex have both spatial and non-spatial correlates. Deshmukh & Knierim [35] demonstrated that a small but significant number of LEC cells (but not perirhinal cells; [41]) showed spatial firing that strongly resembled hippocampal place fields when there were objects present in the environment. Importantly, these putative place fields were at locations where the animal had never experienced objects.…”