Memories forever in our brains

Introduction

This page is the fourth part of a study of the article

Engineering a memory with LTD and LTP

by researchers from the university of California at San Diego and the Howard Hughes Medical Institute

Summary

Thus article presented 2 experiments, both using cued fear conditioning on rats trained to press a lever.

A virus was used to insert receptors sensitive to light to be able to make a light directly to the brain be a CS.

This CS was associated to an electric shock and the conditioned response was less pressing of a lever.

With the 2 experiments , we can conclude 2 things by assuming that LTO and LTD is the mechanism of memory.

1) A memory once formed in the brain is still there even if we can’t remember it.

The induction of LTD in memory was able to block the association and the CR. However, this was reinstated by LTP.

If a memory is caused by LTP and is forgotten by LTD, This result shows that even after being forgotten, there is no need of recreating the memory from nothing.

All that needs to be done is the restrengthening of the memory.

2) Extinction is or the creation of a new memory or a way to completely erase the previous memory

In the second experiment, they caused an extinction of the fear conditioning.

In this case, unlike all the results until then, the CR didn’t reappear after LTP induction.

This leaves 2 possible cases.

The extinction caused a new stronger memory saying the tone isn’t associated with the shock.

However, if it was a distinct new memory, the LTP induction would have caused the associating memory to be stronger thus the CR would have come back.

This means in this case, it was more probable that the original memory was changed from “ tone = electric shock “ to “ tone = no electric shock”.

The original memory was completely erased.

This means instead of an association of “ tone = no electric shock” appearing, the original association completely disappears during the process of extinction.

For this to happen, neural connections and circuits of this memory have to be fully cleared.

However, this would be a problem following the first conclusion we reached.

If this is the case, maybe LTP isn’t the mechanism of memory at all…

Part 1 : What is fear conditioning and how is it used ?

Part 2 : Finding LTP in conditioning

Part 3 : The brain and memory, simple but complex engineering