HTM School 14: Grid Cells

Is this “remembering” in any way independent, or it is simply fresh memories in association cortices forming temporary connections in hippocampus, for potential reinforcement?

It is likely that the hippocampus does good one-shot episodic learning as opposed to slower Hebbian learning in the cortex. It is possible that sleep spindles power an accelerated learning in the cortex.

Do these spindles also happen in awake hippocampus, although less frequently?

If the hippocampus is learning the “delta” between what is in the cortex and hippocampus I could see that part of the process is to “ring” both to test the response and drive learning to the cortex until they are in agreement.

Isn’t this agreement between cortex and amygdala, with hippocampus as a mediator?

The claims that spatial processing is done in the hippocampus seems off - patients with damage to the hippocampus see to be able to process space normally - they just can’t form new memories.

Well, temporary hippocampal connections can also be with spatial memories in the cortex.
So, my “map” idea should be qualified in that this mapping is temporary.
Still, all association cortices must have tentative / potential connections with hippocampus, so it’s kind of a proto-map.

1 Like

No.

1 Like

I don’t see it this way. There is a strong spatial component to what the hippocampus does. I think that the amygdala “colors” episodes but does not contain them.
This patient may help frame the behavior of the amygdala:

Note the preserved function which helps frame what the amygdala does and does not do.

This quora entry has some interesting pointers if you wish to explore further:
https://www.quora.com/If-all-humans-were-born-without-the-Amygdala-part-of-the-brain-would-humans-become-more-docile-and-less-likely-to-fight-each-other

2 Likes

Thanks. So, I guess hippocampus mapping to cortex is indirect, via thalamus.
At least outside of EC and medial temporal lobe.
As for intrinsic function, that seems to be search for correlations between fresh memories.
Because they are conveniently localized in hippocampus but widely distributed in the cortex.
This covers spatial aspect too: the sources of short-term memories are likely proximate spatially.

1 Like

I have not been able to locate the exact mechanism/neural pathway that feeds images to the amygdala (and more importantly - parses) but it does seem to be aware of shapes, and to a lesser degree places, to activate emotional responses.

in general, this post has contributing amygdala content:

and in particular this link speaks to my point:

This link ties the amygdala to the hippocampus and hopefully - brings this post more in alignment to this thread:

1 Like

I think you are talking about blindsight: https://en.wikipedia.org/wiki/Blindsight,
which is probably via LGN or Superior Colliculus: https://en.wikipedia.org/wiki/Superior_colliculus

1 Like

In general - yes.

I am very aware of sub-cortical visual awareness.

What I am less sure of is the perceptual mechanism. “We” have a pretty good idea of the general mechanism of the visual path and contents of the cortical visual stream.

I have not seen the same level of description and understanding of this sub-cortical visual perception.
This is important and related to grid cells in an indirect way.

As far as I am aware - nobody really knows how the visual, tactile, and somatosensory information is combined at the level of the hippocampus to form the response or activation pattern that is described in the Moser work. If a mouse navigates by vision or motion or whiskers it all seems to end up forming the same response to locations that have come to be known as grid and place cells.

Most of the work I have seen comes at this from the cortex side. @Gary_Gaulin put up a post today that analyses the relationship between the grid & place cells and if you read this it would seem like this is somehow happening in isolation from the rest of the brain.

My point in all this is that the cortex pathway seems to lead from the raw sensory areas through the WHAT and WHERE streams to the temporal lobe and on into the entorhinal cortex. This is a pathway that is full of learning and serial processing.

The sub-cortical structures seem to be shorter and more hardwired. They come to the hippocampus via the “other” direction and may well play as a significant pathway to forming the place and grid patterns.

This is the bit that I have been trying to learn more about: the hardwired visual system in the sub-cortical structures.

We know it has built in shapes and emotional coding for at least fear. We know that it can guide you around a room when you can’t see at all. It can guide your grasping when blind. It sees faces and expressions. There it good reason to think that it uses features to be sexually attracted - sex linked features that are thought to signal desirables in a potential mate. I’m sure I could name more but this is just a random list. Yes - the male and female brains could be wired/programmed differently.

That’s a lot of lower level processing and it’s tied directly to the hippocampus. It sure would be nice to know more about a few dozen dense cluster of nerves that are doing all this.

1 Like

My impression is that sub-cortical perception is much lower-quality, the only advantage is that it’s faster.

1 Like

I think this does well as an answer to your questions!

3 Likes

Thanks for that! This was a very interesting read! I learned very much about how the hippocampus and entorhinal cortex work together to represent location.

However, even after trying to pay close attention to the most interesting and salient information, I’m still unsure how to answer my own questions. The paper was mostly about hippocampal place field locations and place cell remapping, so I still don’t know much about grid cell dynamics or their relationship with sensory input.

1 Like

One thing I noticed was the huge emphasis on firing rate remapping and rate encoding. Such as this snippet

“the hippocampus can simultaneously convey information related to the position of an animal and to the cues present in the environment. During rate remapping, the integrity of the spatial code is preserved because place fields are stable, but the precise firing rate of neurons varies to encode information not related to the current position of an animal.”

This sounds like an important feature of the brain.

2 Likes

Did you get anything out of figure 3?

Section 3 does call out related papers - I have not looked at them but it may be a good point to dig deeper.

That said - I picked up on that you are looking to see how the senses end up forming these patterns in the EC.

Let me make it clear that nobody knows this.

My twitter feed is full of ads for post-doc positions to research this very question. Whoever does figure this out will prolly score on a Nobel prize for it.

2 Likes

Right I think. I just had these questions after watching Matt’s demo where you can see the grid cells firing when the mouse’s location enters their firing fields. I started to think about how those modules can create the hexagonal grid pattern to encode an environment as large and diverse as the world. I guess I would just need more info about the input to EC.

2 Likes

I just saw this paper today in my twitter feed. It does not directly answer the question of how the senses are encoded in the hippocampus but it does offer more insight into the general topic of coding and retrieval in the medial temporal area:

Reactivated spatial context guides episodic recall - Nora A. Herweg, Ashwini D, Sharan, Michael R.Sperling, Armin Brandt, Andreas Schulze-Bonhage, Michael J. Kahana

2 Likes

And here is another on time representation in lateral EC: https://neurosciencenews.com/time-perception-9771/

3 Likes

I think I can better articulate my inquiry after thinking this over for a few days.

So, the goal of these grid cells is to uniquely represent each location in an environment by having the hexagonal lattice “cover over” all possible locations of that environment with equally spaced place fields.

Assuming that is an accurate premise, then the question is: how would I initialize these place fields for a given set of grid cells (in modules), assuming this is the very first environment to be learned, so no previous place fields exist? And then how would they grow to represent the environment as it is explored?

AFAICT, you can’t create the grid before you know the extent of the environment, so it has to start from nothing and then be learned through movement, right?

I don’t expect the answer to this to be biologically accurate really, since I highly doubt this is known. Who knows.

I figured I might as well pose this questioning here while I try to hack up my own (probably dumb) solution.

2 Likes

We have been talking about the spatial component of memory and how that may play out in the hippocampus.
This paper adds some interesting fuel to that fire:

With code:

and the dataset to feed into the process:
https://dataspace.princeton.edu/jspui/handle/88435/dsp01nz8062179

1 Like

We talk about place, direction, edge cells as normal spatial functions of the hippocampus/entorhinal cortex.

For a while now I have been saying that the entire personal experience is coded in this system - not just spatial dimensions. Here is how another major chunk of your experience shows up in this coding:

1 Like

Hello, I am currently trying to do research on Grid cells and am attempting to train a model with grid cell data. I was wondering if anyone knows of any grid cell data sets, specifically images of grid cells (brain scans). If so this would we really helpful as I can’t seem to find any

You might find what you need here:

We have started the process of uploading raw data from studies of entorhinal cortex and related regions for open access. So far key data from Sargolini et al (2006) and Hafting et al (2008) have been uploaded but more will come. Our intention is to make all raw data from all published studies available. The data contain a lot more interesting information than what has been published and we encourage users to dig further. Please do not hesitate to contact us for updates and information (edvard.moser@ntnu.no).

https://www.ntnu.edu/kavli/research/grid-cell-data

And some background:
https://www.ntnu.edu/kavli/discovering-grid-cells

1 Like