Identifying Core Regions for Path Integration on Medial Entorhinal Cortex of Hippocampal Formation.

Ayako Fukawa,Hiroshi Yamakawa,Ikuko Eguchi Yairi,Takahiro Aizawa

doi:10.3390/brainsci10010028

Abstract

Path integration is one of the functions that support the self-localization ability of animals. Path integration outputs position information after an animal’s movement when initial-position and movement information is input. The core region responsible for this function has been identified as the medial entorhinal cortex (MEC), which is part of the hippocampal formation that constitutes the limbic system. However, a more specific core region has not yet been identified. This research aims to clarify the detailed structure at the cell-firing level in the core region responsible for path integration from fragmentarily accumulated experimental and theoretical findings by reviewing 77 papers. This research draws a novel diagram that describes the MEC, the hippocampus, and their surrounding regions by focusing on the MEC’s input/output (I/O) information. The diagram was created by summarizing the results of exhaustively scrutinizing the papers that are relative to the I/O relationship, the connection relationship, and cell position and firing pattern. From additional investigations, we show function information related to path integration, such as I/O information and the relationship between multiple functions. Furthermore, we constructed an algorithmic hypothesis on I/O information and path-integration calculation method from the diagram and the information of functions related to path integration. The algorithmic hypothesis is composed of regions related to path integration, the I/O relations between them, the calculation performed there, and the information representations (cell-firing pattern) in them. Results of examining the hypothesis confirmed that the core region responsible for path integration was either stellate cells in layer II or pyramidal cells in layer III of the MEC.

Highlights

The hippocampal formation is the brain region that controls the memory of vertebrate animals.This region is deeply involved in spatial memory, such as spatial learning and spatial searching.Actions that require spatial memory for appropriate route selection while obtaining environmental information in a space and reaching destinations are called “navigation”
This paper reviewed extensive knowledge to elucidate the detailed structure at the cell-firing level of medial entorhinal cortex (MEC) that is the core region responsible for path integration
This paper reviewed various articles on regional, neural circuit, and cell-firing-pattern levels related to path integration

Summary

Introduction

The hippocampal formation is the brain region that controls the memory of vertebrate animals.This region is deeply involved in spatial memory, such as spatial learning and spatial searching.Actions that require spatial memory for appropriate route selection while obtaining environmental information in a space and reaching destinations are called “navigation”. The hippocampal formation is the brain region that controls the memory of vertebrate animals. This region is deeply involved in spatial memory, such as spatial learning and spatial searching. Brain Sci. 2020, 10, 28 found in the rodent hippocampus and named “place cells” [4,5]. This discovery led to the thought that the hippocampus plays an essential role in the formation of cognitive maps in mammals. MEC has “grid cells” that fire simultaneously with place cell firing when an animal is in a specific place in the environment [7]. Grid cells are involved in realizing path integration; both they and place cells are present in different places in the hippocampal formation, and the number of cells that fire is different [7]

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