1) A neuron of the entorhinal cortex

"I live in the fifth layer of the entorhinal cortex. I participate in memory formation.

That particular time when Mouse Ann was placed in a cage and received a shock there I also became active. Like many other animals including humans, Ann easily remember threatening situations to avoid them in the future.

I am a neuron, so I transmit information to some other neurons (action potential goes down my axon and neuromediators are released at the end. They influence the activity of other neurons, including neurons in prefrontal cortex).

These "letters" that I send to the prefrontal cortex during such important events lay the groundwork for further long-term memory consolidation. Without these letters, the event will only affect behavior for about a week. If these letters do not reach the recipient, after two to three weeks, this event no longer affects behavior, and Mouse Ann will no longer fear the cage where she received a shock"

2) A neuron of the prefrontal cortex

"So Mouse Ann ended up in a new cage and received an electric shock there.

I am one of those neurons in the medial prefrontal cortex in which the shock caused a significant increase in calcium currents (that molecular abacus, remember? Neurons use ions like Potassium, Sodium and Calcium to propagate information from one place to another). Just 15 minutes later after that initial calcium current, It already had an effect on my nucleus: special parts of my DNA are being "read" so information withing them would help me deal with this new situation.

These genes are called "immediate early genes". They launch synthesis of new proteins within me.

For example, the protein c-Fos began to be synthesized more - it is an early response protein. In turn, c-Fos initiated the synthesis of other proteins important for the formation of long-term memory and necessary for the formation of new synapses.

This allows me to become a part of the memory 'engram' of that incident when Mouse Ann was shocked in the cage.
That incident also prompted me to change my shape, and as you might remember, changing the shape of the neuron helps change how it handles the incoming information. After that incident with the cage, the number of synapses on my dendrites increased.

On the 12th day after the shock, I had many more synapses compared to the 2nd day after the shock. If Mouse Ann ever enters that cage again I will reactivate, and trigger the memory of the previous shocking event."
3) c-Fos protein.

I am a protein in a cell that lives in prefronal cortex. My structure is encoded in a gene called FOS, one of "immediate early genes", so important for memory. If you block FOS, memory will not be formed.

But it's function is so much more than just memory.

In many cells, when something important happens (learning, radiation, action of inflammatory factors, bacterial or viral infections), I am in the front lines and immediately begin to be synthesized. In this particular cell right now, I also come to the rescue when something important happens. If the mouse had simply entered a new environment and not received a shock, I would not have appeared.

It was the neuron of the entorhinal cortex that triggered my appearance. If the entorhinal cortex neuron couldn't send its letters to the neuron in the prefrontal cortex where I reside, I wouldn't have appeared.

I bind with another early response protein and form with it AP1 - activating protein-1. This protein binds to DNA, initiating gene transcription and thus protein synthesis. Thus, I help convert extracellular signals into the initiation of protein response synthesis. I am a cornerstone of memory.

4) A group of neurons that formed the 'memory engram' in the prefrontal cortex

I am a neuronal network.

While neurons of which I consist existed long before me, and they participated in numerous other networks before, I started to exist when Mouse Ann got shocked in the cage. Neurons that were ready to form a memory engram by that time co-activated, connections between them strengthened. So a new network was formed.

These are the neurons that receive information from the entorhinal cortex and began to synthesize c-Fos after the shock.

I am the anchor through which memory will transition into long-term form. As a network, I am needed for the formation of long-term memory. I am not needed for several days after learning. Other brain areas can cope without me: for example, If on the 2nd day after the shock Mouse Ann enters this horrible cage again and my activity is for some reason suppressed, Mouse Ann will show the fear this cell.

But if my activity is suppressed when Mouse Ann enters there a week later, Mouse Ann will behave as if not afraid of this cell. So I am critically important specifically for long-term memory. On the 12th day after the shock, my neurons grew many more synapses than on the 2nd day after the shock. This allows them to receive new information and process it differently.

5) Amygdala

I am like a little city. I have various nuclei, housing many different neurons within me.

When Mouse Ann felt the shock, I received information about it from various sources. One of these sources is the neurons of the 5th layer of the entorhinal cortex. If during the shock their letters are intercepted so that they do not reach me, both short-term and long-term memory are disrupted.

I help protect Mouse Ann. If she ever enters this unfortunate cage again, I will activate.

If this happens immediately after learning, I will need letters from the entorhinal cortex.

However, after several weeks from initial incident, when the engram of long-term memory in the prefrontal cortex has already been consolidated, the prefrontal cortex sends me letters. When I receive these letters, I initiate defensive reactions, and Mouse Ann freezes, thus hoping to avoid danger."

6) Hippocampus

I am important for many processes, including memory. If I am damaged, humans and mice lose the ability to form new memories (new episodic memories to be exact).

Interestingly, they also forget what happened shortly before the damage. It means that I am critically important for the formation of new memories, as well as for remembering recent events. I am no longer needed for remote memories. Therefore, people with damage to the hippocampus remember old events from their lives but cannot memorize new ones.

During everyday life, engrams of cells are formed within me, reflecting each event.

These engrams form very quickly.

Previously, it was believed that After learning I slowly transmit this information to the cortex, mainly during sleep, thus "teaching" the cortex so it would get the knowledge that I have. However, recent studies have shown that the engram in the prefrontal cortex is formed right at the moment of learning as well, but it is not yet functional for a few days after event.

That is, during sleep, I am not teaching the cortex something it didn't know before me but rather helping the existing memory engram to mature, so it would be useful and I would no longer be needed.

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