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So I understand that place cells form a map of each environment the subject has been in and responds accordingly in each environment. Question is how do they switch to represent a different environment when the subject moves to a new environment? It seems unlikely that a different set of place cells represent each environment the subject has ever encountered because it seems that would require too many place cells (and since the cell counts in the hippocampus is I presume relatively fixed, "free" place cells run out at some point), so it must be the same place cells "remembering" different response patterns to different environment and responding accordingly in different environments.

From the wikipedia page on place cells: "In a different environment, typically about half the place cells will still have place fields, but these will be in new places unrelated to their former locations."

Muller, R. U.; Kubie, J. L. (1987). "The effects of changes in the environment on the spatial firing of hippocampal complex-spike cells". The Journal of neuroscience : the official journal of the Society for Neuroscience.

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    $\begingroup$ Please, to the people who are voting to close: do not vote to close on a question as unclear simply because the question is an area outside of your expertise. It is possible to edit this question slightly to clarify, but this is actually an excellent question and actually provides a fair amount of background information and even includes an external reference. $\endgroup$ – Bryan Krause Mar 13 '17 at 21:03
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Imagine a 2x2 grid. Starting on the bottom left, how many different ways can you move to each box of the grid?

Two times: 1) up, right, down; 2) right, up, left

Now, say each of those combinations are used to store the memory of a different location. In order to activate either sequence, a different input signal would be required to tell the axon to send it's initial signal right, or up.

Your eyes will receive a signal in the form up light, and a specific electrical impulse will be sent down the optic nerve that allows your brain to perceive an image.

There are millions of nerves in your brain, and each combination of impulses serves to store a different memory.

Now, imagine a grid that has a million by a million boxes. How many combinations can you use to fill each box?

And, actually if I recall correctly, the hippocampus is one of the few areas in the brain that is consistently undergoes neurogenesis.

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  • $\begingroup$ This answer does not attempt to answer the question asked: "how do place cells switch their response patterns in different environments?" $\endgroup$ – Bryan Krause Mar 13 '17 at 21:04
  • $\begingroup$ "Different input signals"... ie. from a different combination of signals from, what was my example, the optic nerve. $\endgroup$ – Bob Mar 13 '17 at 22:15
  • $\begingroup$ But how are those signals different? The optic nerve isn't rewiring to connect to different cells in visual cortex when you move from one building to another. You are answering the question "How does a radio tune to different stations?" by saying "Well your radio just listens to different stations depending on what you set the dial": it is essentially just re-stating the question, rather than providing an answer. $\endgroup$ – Bryan Krause Mar 13 '17 at 22:21
  • $\begingroup$ Do you think the optic nerve consists of a single neuron? $\endgroup$ – Bob Mar 13 '17 at 22:24
  • $\begingroup$ Absolutely not. I should have been more precise in my comment to say "axons of the optic nerve aren't" rather than the shorthand I used. $\endgroup$ – Bryan Krause Mar 13 '17 at 22:26
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It is true that individual place cells will fire in many different environments. However, the exact location where a place cell fires will vary in different environments. Moreover, two place cells that fire in the same location in one environment could fire in completely different locations in a second environment. Therefore, the pattern of activity of the network as a whole can be unique for each location in each environment. The term for this scrambling of the association between place cells and locations in different environments is called "global remapping".

Try: L. L. Colgin, E. I. Moser, M.-B. Moser, Trends Neurosci. 31, 469–77 (2008). for a review. http://www.cell.com/trends/neurosciences/abstract/S0166-2236(08)00167-7?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0166223608001677%3Fshowall%3Dtrue

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  • $\begingroup$ why the downvote? $\endgroup$ – honi Mar 15 '17 at 5:22
  • $\begingroup$ Can place cells be seen like the pixels on a screen, in that the same pixels can represent an infinite amount of pictures because it's the pattern of their activation as a group that actually matters, or is the analogy a bad one? $\endgroup$ – Oosaka Mar 15 '17 at 8:43
  • $\begingroup$ that is a good analogy $\endgroup$ – honi Mar 15 '17 at 16:07
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So I'll try to answer my own question.. Not sure if that's usual but apparently it's allowed.

Ok. I think the question is fundamentally mistaken. Place cells do not "switch" into a different mode when the subject moves to a new environment. Rather, in a new environment, the inputs to these place cells are different, other parts of the brain is telling the hippocampus it is now in a different environment, so naturally, the place cell responds in a different manner. In this sense the place cell is a "computer" (might be using the word too loosely but hopefully it makes sense), it makes a different output based on information from the senses.

This is my understanding. Hopefully it makes sense.

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