Shedding light on stellate cells

Layer II of the medial entorhinal cortex (MEC) contains two principal cell types: pyramidal cells and stellate cells. Accumulating evidence suggests that these two cell types have distinct molecular profiles, physiological properties, and connectivity. The observations hint at a fundamental functional difference between the two cell populations but conclusions have been mixed. Here, we used a tTA-based transgenic mouse line to drive expression of ArchT, an optogenetic silencer, specifically in stellate cells. We were able to optogenetically identify stellate cells and characterize their firing properties in freely moving mice. The stellate cell population included cells from a range of functional cell classes. Roughly one in four of the tagged cells were grid cells, suggesting that stellate cells contribute not only to path-integration-based representation of self-location but also have other functions. The data support observations suggesting that grid cells are not the sole determinant of place cell firing.

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Field repetition and local mapping in the hippocampus and the medial entorhinal cortex

Journal of Neurophysiology ◽

10.1152/jn.00933.2016 ◽

2017 ◽

Vol 118 (4) ◽

pp. 2378-2388 ◽

Cited By ~ 8

Author(s):

Roddy M. Grieves ◽

Éléonore Duvelle ◽

Emma R. Wood ◽

Paul A. Dudchenko

Keyword(s):

Entorhinal Cortex ◽

Local Area ◽

Place Cells ◽

Grid Cells ◽

Medial Entorhinal Cortex ◽

Pattern Completion ◽

Global Space ◽

Local Environments ◽

Neural Substrate ◽

The Relationship

Hippocampal place cells support spatial cognition and are thought to form the neural substrate of a global “cognitive map.” A widely held view is that parts of the hippocampus also underlie the ability to separate patterns or to provide different neural codes for distinct environments. However, a number of studies have shown that in environments composed of multiple, repeating compartments, place cells and other spatially modulated neurons show the same activity in each local area. This repetition of firing fields may reflect pattern completion and may make it difficult for animals to distinguish similar local environments. In this review we 1) highlight some of the navigation difficulties encountered by humans in repetitive environments, 2) summarize literature demonstrating that place and grid cells represent local and not global space, and 3) attempt to explain the origin of these phenomena. We argue that the repetition of firing fields can be a useful tool for understanding the relationship between grid cells in the entorhinal cortex and place cells in the hippocampus, the spatial inputs shared by these cells, and the propagation of spatially related signals through these structures.

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A geometric attractor mechanism for self-organization of entorhinal grid modules

eLife ◽

10.7554/elife.46687 ◽

2019 ◽

Vol 8 ◽

Cited By ~ 7

Author(s):

Louis Kang ◽

Vijay Balasubramanian

Keyword(s):

Entorhinal Cortex ◽

Network Models ◽

Recurrent Inhibition ◽

Modular Structure ◽

Self Organization ◽

Periodic Lattice ◽

Grid Cells ◽

Medial Entorhinal Cortex ◽

Attractor Network ◽

Discrete Values

Grid cells in the medial entorhinal cortex (MEC) respond when an animal occupies a periodic lattice of ‘grid fields’ in the environment. The grids are organized in modules with spatial periods, or scales, clustered around discrete values separated on average by ratios in the range 1.4–1.7. We propose a mechanism that produces this modular structure through dynamical self-organization in the MEC. In attractor network models of grid formation, the grid scale of a single module is set by the distance of recurrent inhibition between neurons. We show that the MEC forms a hierarchy of discrete modules if a smooth increase in inhibition distance along its dorso-ventral axis is accompanied by excitatory interactions along this axis. Moreover, constant scale ratios between successive modules arise through geometric relationships between triangular grids and have values that fall within the observed range. We discuss how interactions required by our model might be tested experimentally.

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Cholinergic Modulation of the Resonance Properties of Stellate Cells in Layer II of Medial Entorhinal Cortex

Journal of Neurophysiology ◽

10.1152/jn.00492.2009 ◽

2010 ◽

Vol 104 (1) ◽

pp. 258-270 ◽

Cited By ~ 58

Author(s):

James G. Heys ◽

Lisa M. Giocomo ◽

Michael E. Hasselmo

Keyword(s):

Patch Clamp ◽

Resonance Frequency ◽

Entorhinal Cortex ◽

Stellate Cells ◽

Cholinergic Modulation ◽

Medial Entorhinal Cortex ◽

Whole Cell ◽

Whole Cell Patch Clamp ◽

Resonance Properties

In vitro whole cell patch-clamp recordings of stellate cells in layer II of medial entorhinal cortex show a subthreshold membrane potential resonance in response to a sinusoidal current injection of varying frequency. Physiological recordings from awake behaving animals show that neurons in layer II medial entorhinal cortex, termed “grid cells,” fire in a spatially selective manner such that each cell's multiple firing fields form a hexagonal grid. Both the spatial periodicity of the grid fields and the resonance frequency change systematically in neurons along the dorsal to ventral axis of medial entorhinal cortex. Previous work has also shown that grid field spacing and acetylcholine levels change as a function of the novelty to a particular environment. Using in vitro whole cell patch-clamp recordings, our study shows that both resonance frequency and resonance strength vary as a function of cholinergic modulation. Furthermore, our data suggest that these changes in resonance properties are mediated through modulation of h-current and m-current.

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