NPB162-Journal-5

Hippocampal remapping and grid realignment in entorhinal cortex, 2007

Marianne Fyhn, Torkel Hafting, Alessandro Treves, May-Britt Moser Edvard I. Moser

1- What is the research question / hypothesis driving this study?

“To determine how neural activity in grid
cells is organized at the ensemble level and how their organization
might influence the formation of representations downstream in the
hippocampus”
Find out how grid cells are organized jointly, and how that affects representation later in processing streams

2- What is the experimental design of the study? (How are they trying to answer the question?)

First they induced global and rate remapping
- Global remapping was induced by two different procedures, one in which the rat was tested in the same location in either a square or a circular enclosure7,9,21,22 (Fig. 1a) and another in which the animal alternated between similar square boxes in two different rooms6,13,14 (Fig. 1b).
- Rate remapping was induced by changing the walls of a square recording enclosure from a three black and one white configuration to a one black and three white configuration14 (Fig. 1c). This induced consistent rate remapping in all seven experiments in which CA3 cells were recorded
Then they observed firing patterns of grid cells in MEC

3- What did you learn from Figure 1a-c? (once sentence)

We can see that conditions ‘a’ and ‘b’ (box->circle->box and box-new box->old box) both induce global remapping, where firing rate and firing location where changed. Condition ‘c’ (wall colors where changed) caused rate remapping, where location sensitivity is similar but relative firing rates are changed.

4- What did you learn from Figure 1d-h? (once sentence)

It shows us graphically that all of them underwent rate remapping, and ‘a’ and ‘b’ underwent spatial remapping while ‘c’ did not

5- What did you learn from Figure 2? (1-2 sentences)

We can see that there is a consistent, population representation in grid cells. For AxA’, there is little displacement, while for AxB we see a large displacement, and a large distinction in significance in the cross-correlogram.

6- What did you learn from Figure 3? (1-2 sentences)

The representation of the grid cells from A to be shows some similarity if B is rotated. While initially we saw very little similarity in the cross-correlograms, after rotating B we find that they have a more similar structure.

6- What did you learn from Figure 4? (1-2 sentences)

Despite rate remapping of the place cells in CA3, the grid cells in entorhinal cortex retain their representation. AxA’ and even AxB show very little displacement, and a high similarity in their cross-correlogram.

7- What is the overall conclusion from the article?

The representation of space through grid cells and their dynamics are linked to the type of remapping occurring in CA3 place cells. Rate remapping is associate with a stable grid field, while global remapping is associated with a coordinate shift in the grid cells. They conclude that ensembles of grid cells are maintaining a constant spatial space structure

8 - What was the most confusing aspect of the article?

The mathematical terms, orthogonal/cross-correlograms/temporal population vectors. I somewhat get the idea of what they’re getting at, but I would have loved to have a introduction to the terms they would be using to analyze the data so that I could more smoothly understand what the results were, and how they were getting them.

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