Grid Cells and Place Cells: An Integrated View of their Navigational and Memory Function

Abstract

Much has been learned about the hippocampal/entorhinal system, but an overview of how its parts work in an integrated way is lacking. One question regards the function of entorhinal grid cells. We propose here that their fundamental function is to provide a coordinate system for producing mind-travel in the hippocampus, a process that accesses associations with upcoming positions. We further propose that mind-travel occurs during the second half of each theta cycle. By contrast, the first half of each theta cycle is devoted to computing current position using sensory information from the lateral entorhinal cortex (LEC) and path integration information from the medial entorhinal cortex (MEC). This model explains why lesions can abolish hippocampal phase precession but not place fields.

Human vicarious trial and error is predictive of spatial navigation performance

“…Therefore, this shows that VTE events occur even when the internal representation of space has been learned, rejecting the hypothesis that VTE serves the sole purpose of boosting the learning of the environmental sensory-statistics at the neuronal level. The hippocampal neural mechanisms for simulating spatial trajectories have been proposed both theoretically and computationally 17,18 . Additionally, a model of spatial representation and trajectory simulation has been implemented in a robotic simulation of the T-maze navigation task and suggested the emergence of VTE behaviors at early learning phases 19 .…”

“…This increase in available sensory information could potentially increase the number of hippocampal place-cells tuned to the spatial locations of each of the maze-arms, as observed in 9 , thereby optimizing performance. On the other hand, aligning one's body towards possible decision options would allow the setting of path-integration hippocampal mechanisms to simulate future trajectories, as has been theoretically and computationally postulated 17,18 . Indeed, hippocampal mental time-travel has been observed to occur when the animal performs VTE behaviors 4 .…”

Qualitative differences in memory for vista and environmental spaces are caused by opaque borders, not movement or successive presentation

“…Right: Number of participants revealing best fit to either of three order clusters (along rows/columns, along object presentation during the placement task and along corridor based encounter) when rearranging the object layout from memory. mentally walking down the route (Byrne et al, 2007;Sanders et al, 2015) or of constructing a mental model of the non-visible environment parts from one's current location (Meilinger, 2008), however, remains an issue to exam further. The layout itself was not responsible for the corridor distance effect, since the effect was not evoked by VS learning.…”

“…This successive activation has been proposed to correspond to mind (i.e., nonphysical) travel -or mental walk -along a route (Byrne et al, 2007;Sanders et al, 2015). Path integration along mind travel may then be used to estimate a vector towards the goal.…”

“…One possible explanation for this increasing error with distance could indeed be that during task execution (retrieval process), memory of the environmental space is retrieved successively, along the route from which the environment was experienced from. This might be realized, for example, by mentally walking down the memorized route starting from the current location and approaching the target (Byrne, Becker, & Burgess, 2007;Sanders, Rennó-Costa, Idiart, & Lisman, 2015) or by constructing a mental model of the nonvisible parts of the environment corridor-by-corridor from one's current location (Meilinger, 2008). Both theories predict an increase in computational effort for larger distances (route distance or amount of corridors) between current and target location, since spatial information must be activated successively following the encoding procedure.…”