Parahippocampal Spatial Navigation: The Role of the Grid Cell

Ariel K. Feldman, Program in Neural Computation

A Brief History of Spatial Understanding

Drivers of CA1 Spatial Firing

Park et al., PLOS ONE 2019

Removal of DG & CA3 intrahippocampal inputs

EC-CA1 connection sufficient for spatial recollection

Layers II/III of Medial Entorhinal Cortex (MEC) to CA3/CA1

MEC Projections

University of Bristol Center for Synaptic Plasticity

Perforant pathway

Layers II/IV -> DG & CA3

Layers III/V -> Subiculum & CA1

^ From here

Grid Cells

What is a Grid Cell?

Found in Layer II of MEC

Stellate & pyramidal cells

Tang et al., Neuron 2014

Voltage-dependent intrinsic oscillations faster than theta?

Representation of interference?

A Metric for Spatial Representation

Moser, Rowland & Moser, Cold Spring Harbor Perspectives in Biology 2015

Population code with similar precision

Periodic triangular spatial firing arrays

Metric system of spatial navigation

Computations in EC instead of H?

Neurobiological Correlates

Topography of Grid Cell Firing

Spacing

Orientation

Dorsomedial -> ventrolateral increases monotonically

Similar for colocalized neurons; underlying topography unknown

Similar to place field size along dorsoventral axis

Topography of Grid Cell Firing

Phase

Colocalization had no impact

Same spacing/orientation; slight phase shift superimposition

Hafting et al., Nature 2005

Firing vertices shift randomly

Entorhinal Cortex Architecture

Periodic bundling of pyramidal dendrites and axons -> modularity?

Correlation to functionally segregated grid maps?

Little to no evidence as of yet

Information in Population Activity

Modules

Single cells have hexagonal firing fields

Relative firing positions form rhombus shape

Unified in scale/orientation, differ in firing position

Bush et al., Neuron 2015

Modules

Lewis et al., Frontiers in Neural Circuits 2019

Extrinsic Cues & Self Motion

Path Integration

External landmarks (allothetic cues) vs self motion (idiothetic cues)

Self motion the main source for grid maintenance/updates

Grid fields persist despite removal/replacement of salient landmarks

Anchored to boundaries & landmarks in an environment

Basic firing matrix influenced by self motion/path integration

Receive inputs from head-direction cells, boundary cells, etc.

Alignment to Unique Landmarks

Grid rotates with cue card

Indicates phase and orientation are influenced by external cues

Hafting et al., Nature 2005

Questions?