Estimating location without external cues.

Allen Cheung,Olaf Sporns

doi:10.1371/journal.pcbi.1003927

Allen Cheung, Olaf Sporns

Open Access

https://doi.org/10.1371/journal.pcbi.1003927

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Abstract

The ability to determine one's location is fundamental to spatial navigation. Here, it is shown that localization is theoretically possible without the use of external cues, and without knowledge of initial position or orientation. With only error-prone self-motion estimates as input, a fully disoriented agent can, in principle, determine its location in familiar spaces with 1-fold rotational symmetry. Surprisingly, localization does not require the sensing of any external cue, including the boundary. The combination of self-motion estimates and an internal map of the arena provide enough information for localization. This stands in conflict with the supposition that 2D arenas are analogous to open fields. Using a rodent error model, it is shown that the localization performance which can be achieved is enough to initiate and maintain stable firing patterns like those of grid cells, starting from full disorientation. Successful localization was achieved when the rotational asymmetry was due to the external boundary, an interior barrier or a void space within an arena. Optimal localization performance was found to depend on arena shape, arena size, local and global rotational asymmetry, and the structure of the path taken during localization. Since allothetic cues including visual and boundary contact cues were not present, localization necessarily relied on the fusion of idiothetic self-motion cues and memory of the boundary. Implications for spatial navigation mechanisms are discussed, including possible relationships with place field overdispersion and hippocampal reverse replay. Based on these results, experiments are suggested to identify if and where information fusion occurs in the mammalian spatial memory system.

Highlights

Accurate spatial navigation is crucial to animal survival
Localization is robust despite the presence of noise modelled from the rodent head direction system, and even inaccuracies in the navigation system’s memory of the boundary or internal models of noise
Rotational asymmetry can arise from interior structures such as barriers or voids, without contact information

Summary

Introduction

Accurate spatial navigation is crucial to animal survival. Localization is the process of determining current location, critical for many navigation behaviours. The firing of both place and grid cells strongly correlate with the animal’s physical location in a familiar space [6,7,8,9,10], with firing patterns being stable over days to weeks in the same environment [11] Such neural correlates demonstrate that an animal can robustly localize itself within a familiar arena. Error accumulation due to iPI will lead to a rapid increase in discrepancy between true position and estimated position [14,15,16] It follows that, if using only iPI, a navigation system cannot accurately estimate its location in the long term, and certainly cannot localize itself starting from an unknown pose. An important biological implication is that stable, spatially-selective firing patterns such as those of rodent hippocampal place cells or medial entorhinal grid cells cannot depend purely on iPI

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