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What is a cell assembly?

In Principles of Neural Science Eric Kandel, and colleagues wrote:

After this strengthening has occurred, a group of three neurons that are strongly coupled by excitatory synapses form a cell assembly (Figure E–5C). Neuroscientists generally use this term rather imprecisely. One must look to mathematical models of networks for more precise definitions, which generally have some- thing to do with the presence of strong mutual excita- tory interactions within a group of neurons. The word “assembly” emphasizes that the group did not initially exist but was constructed through the strengthening of the synapses of the neurons in the group, which in turn was caused by the simultaneous activation of the neurons.

In [1] the cell assembly is defined as:

A large group of cells that tend to be active at the same time because they have been activated simultaneously or in close succession in the past.

Sebastian Seung in [2] defines the cell assembly like this:

... the neurons are excitatory and are mutually connected by synapses into a structure known as a cell assembly.

Hence, my question;

What is the best evidence, if any, for the cell assembly?

Thanks!

[1]: Breedlove, Watson, Rosenberg, Biological Psychology 6th Edition

[2]: Seung, Connectome - How the Brain's Wiring Makes Us Who We Are

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  • $\begingroup$ Have you looked at en.wikipedia.org/wiki/Hebbian_theory? it does mention some experiments. $\endgroup$ – Fizz Jul 8 '18 at 18:45
  • $\begingroup$ If a cell-assembly is self-contained, what role is the computation it is performing? $\endgroup$ – Seanny123 Jul 8 '18 at 21:49
  • $\begingroup$ @Seanny123 a cell assembly(CA) may compute a memory. A CA is a graph. eg a CA w vertices(neurons) A, B, C, D. Edge a connects A to B; edge b connects B, C; edge c connects C,D; edge d connects D,A. in response to some stimulus, you recollect A, which then triggers B, which then triggers C, which then triggers D. $\endgroup$ – user19721 Jul 8 '18 at 22:31
  • $\begingroup$ @Seanny123 I would also like to add this. Since recollecting an event involves thinking, then a cell assembly is also computing thought. $\endgroup$ – user19721 Jul 8 '18 at 22:47
  • $\begingroup$ @Seanny123 So in this sense the cell assembly is self contained. the connections between neurons in a cell assembly are retained without input from the outside. $\endgroup$ – user19721 Jul 8 '18 at 23:00
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EVIDENCE FOR THE CELL ASSEMBLY

The idea of the cell assembly is grounded on the following 3 principles:

  1. The neurophysiological basis of a concept is the cell assembly, ie population coding.

  2. The neurons in a cell assembly continuously fire even after environmental stimulus ceases.

  3. Learning gives rise to cell assemblies through the interaction between presynaptic and postsynaptic synapses.

NOTE I will briefly talk about the first two principles; however, there is evidence for all 3.

EVIDENCE FOR PRINCIPLE 1

In The Organization of Behavior Hebb observed that brain surgery did not affect intelligence. Given this he proposed that the cell assembly was the neurophysiology basis for a concept.

The studies that support this principle show this; different neurons get activated in response to the same feature, but, unless the neurons function collectively, an object is not identified.

(Averbeck 2006) reports that individual neurons count for little; as an example, he mentions the visual cortex. He says:

visual discrimination in the primary visual cortex (V1) is much more accurate than would be predicted from the responses of single neurons.

EVIDENCE FOR PRINCIPLE 2

Principle 2 could explain why a stimulus triggers a memory. Consider this example from Seung, Connectome:

It's a fine spring morning, and you are walking down the street on the way to work. You catch the scent of flowers; within a few steps the smell becomes overpowering. You're not yet conscious of the magnolia blooming at the side of the road, but all of the sudden you're transported far away. You remember standing next to a magnolia tree, outside the red brick house of your first sweetheart. He is holding you in his arms. You feel shy and embarrassed. A plane is flying overhead, and you hear his mother calling for you to come have a glass of lemonade.

He then goes on to explain why this might happen:

How do these connections trigger the recollection of your first kiss? Since the neurons are assumed excitatory, the activation of the "magnolia neuron" excites the other neurons in the cell assembly to become active.

Since neurons in a cell assembly continuously fire even after the stimulus ceases you remain thinking about your first kiss.

Principle 2 is supported by the following studies:

(Funahashi 2001) (Assad 2000)

This post is not great, but I hope it helps someone.

Thanks.

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