The brain and memory, simple but complex engineering

Introduction

This page is the third 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

Engineering

With the ratio of AMPAR to NMDAR response in the synapses and the problem of the NMDAR inhibitor, it can be deduced that LTP is what has created the memory of the optical CS and the shock.

It would be logical to think that LTD, the other constituent of neural plasticity could do the opposite.

The rats who had received paired conditioning ( had formed the LTP in the lateral amygdala ) had an optical LTD induction.

( The LTD induction was done by giving the rats light pulses at a specific frequency, LTP induction was also done in a similar way but with a different frequency and a different number of pulses )

This was able to erase the memory. The rats showed normal pressing of the lever, similar to before they were given cued fear conditioning.

The researchers decided to go on with the experiment and gave the rats with the erased memories an optical LTP induction.

Again, this made the memory reappear.

This cycle could be repeated more times with the same effects and the effects of LTP or LTD were also found to be long term.

They also did the same thing on rats that weren’t conditioned by giving light to the same brain regions and these rats didn’t show any change.

This finding shows us that the optical CS wasn’t activating the neurons for pressing the lever but was playing around with the electric shock – light association.

The second experiment

This was the same experiment as the first but with the optical CS replaced with a tone.

The results were the same.

However they were able to make one additional finding.

After successfully conditioning the rats to associate the tone with an electric shock, they gave the tone multiple times without the shock.

They caused an extinction of the association.

This eventually causes the rat to lose the conditioned response.

However, what was interesting was that LTP wasn’t able to make the CS reappear.

Therefore proving that extinction isn’t equal to LTD.

Next Part : Memories forever in our brains

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

Part 2 : Finding LTP in conditioning