The rodent hippocampus as a bilateral structure: A review of hemispheric lateralization

The rodent hippocampus as a bilateral structure: A review of hemispheric lateralization

This discrete‐continuous hypothesis proposes that the left and right hippocampi contribute to spatial memory and navigation in a complementary manner. Specifically, the left hemisphere stores spatial information as discrete, salient locations, and the right hemisphere represents space continuously, contributing to route computation and flexible spatial navigation.

:scream:

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Hmm… hippocampus appears to be doing a couple of things that seem rather unrelated at first pass. On the one hand, it seems to deal with short term memories, coloring them with good/bad value attribution, and consolidating them into the cortex during sleep. On the other hand, it seems to deal with spatial navigation (where this theory predicts something equivalent to “place” in the left hemisphere, and “location” in the right).

Any theories on how these functions might be related, or is this more likely to be another example of random chance that they ended up in the same apparent structure in the brain?

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Maybe it has something to do with how well quickly we learn to recognize places in the world. They seem like the most complex objects we learn, too, since they’re entire environments.

Episodic and short-term memories are also about entire environments, since they can involve any part of an environment. Maybe it’s one-shot learning of environments.

Another connection is that we constantly have a short term memory of where we are, and we also don’t need to concentrate in order to know the current situation. Unlike specific things like numbers, places and situations don’t require attention to keep in short term memory. I guess places are part of situations.

Reasons the hippocampus seems less involved in attention than the neocortex
  1. Compared to the thalamus, the cortex has more types of pathways connecting it to the thalamus, I think, so it can be more involved in attention.
  2. The thalamic reticular nucleus receives input from the neocortex and inhibits the thalamus, so it’s likely involved in attention. Anterior thalamic nuclei project to the hippocampus and other things, but not the neocortex according to wikipedia. Those nuclei don’t receive input from the thalamic reticular nucleus*, so those might not have that attention mechanism.

*Cited by A Novel T-type Current Underlies Prolonged Ca2+ -dependent Burst Firing in GABAergic Neurons of Rat Thalamic Reticular Nucleus
But my notes say I remembered reading something which contradicts that finding.

We can choose to hold very specific parts of a situation in short term memory, so maybe the cortex chooses to actively remember specific things. For example, if someone tells you to remember the number 45, it takes a moment to stop thinking about what you’re being asked to do and start thinking “45”. You don’t need to pay attention to 45 for a few seconds and you’ll still remember it, but if you wait a minute to start focusing on it, you remember 45 more poorly, e.g. 49. You still remember less specific, more abstract things very well, like being told to remember a number. It would make more sense to me if it remembered something as simple as a number better, but instead it remembers more abstract or complex things better.

In case you meant theories in the literature-

Short-Term Memory and the Human Hippocampus
Hippocampus is thought to be for short term memory of allocentric relationships between objects, whereas parts of the cortex are thought to be for short term memory of egocentric relationships. I guess place in the world fits that, since the animal can see the arrangement of landmarks to know where it is.

https://en.wikipedia.org/wiki/Place_cell

Place cells can activate outside their place fields in a form of replay. Replay is thought to be involved in memory retrieval and consolidation.

Hippocampal Place Cells, Context, and Episodic Memory
The authors suggest place fields are part of a general context function, and time/place are contexts of episodic memories. There are other studies about time cells in the hippocampus (next article is related).

During Running in Place, Grid Cells Integrate Elapsed Time and Distance Run
A couple issues with this are it used treadmills and they found grid fields in a combo of time / space, but grid fields are 2d whereas time is 1d.

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