Selective Erasure of Traumatic Memories Might Soon Be Possible

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Selective Erasure of Traumatic Memories
Credit: Nik Shuliahin (Unsplash)

Have you ever undergone a not-so-memorable experience that later bothered you over and over like a ghost; inviting unnecessary stress every time, and all you prayed was for it to vanish somehow? As per a recently published study in Current Biology by researchers at CUMC (Columbia University Medical Center) and McGill University, your wish might have just been granted.

The Basis

Two Aplysia neurons with synaptic contacts on the same motor neuron.
Two Aplysia neurons with synaptic contacts on the same motor neuron. Credit: Schacher Lab/Columbia University Medical Center

Going by the study, researchers have found out that memories stored in a single neuron of Aplysia*can be selectively deleted. As a result, it might now be possible to develop such drugs that are capable of erasing traumatic memories borne of stressful past happenings, without affecting other important memories.

*Quick Fact:

Aplysia is a marine snail widely known for the large size of its neuron cells. A single neuron’s cell body may measure as much as 1mm in diameter, making it easier for neurobiologists to study its activity.

Theory

It is quite possible for memories to make a home in the brain due to the occurrence of an emotional situation. If the event is of traumatic or stressful nature, it could apparently cause panic attacks even in the far future whenever the person in consideration is exposed to similar situations which might or might not be of traumatic nature.

Dr. Samuel Schacher, neuroscience professor, Department of Psychiatry at CUMC and the co-author of the paper has quoted an example: Consider that, you are walking in an area with a high crime-rate, and you take a shortcut through a dark alley where you get mugged; assume that you happen to see a mailbox nearby around the same time. Consequently, you might get nervous every time you go to post mail or see a mailbox later on.

The nervousness that you would feel later in life at the sight of mailboxes is a non-associative memory*. It has nothing to do with the trauma directly, but being an element on-site, it becomes a persistent part of the memory; reminding you to stay alerted and act with caution.

*Quick Fact:

1. Associative Memory is that which connects, learns and remembers, the association between distinct items/stimuli that are involved in a set-up.
For example, remembering faces and names to go with them, i.e., we associate the names of the people we meet with their faces.
In the example mentioned above, linking a dark alley to being alert is an associative memory.

2. Non-Associative Memory is that in which no linking takes place. The stimuli do not get associated.
As mentioned in the example quoted by Dr. Schacher, the anxiety felt in the proximity of a mailbox is not directly related to the incident of mugging, and is hence a non-associative memory.


Dr. Schacher further adds that the main aim of the research is to be able to eliminate troublesome non-associative memories that have been embedded in the brain during stressful situations, without inflicting any harm on the complementary associative memories from the same situations.

Understanding the Research

Our brain functions, owing to the vast interconnected networks of *synapses.

*Quick Fact:

Synapse is a structural entity that allows a neuron to transmit information to another neuron.


*Synaptic plasticity
refers to the strengthening or weakening of synapses over the time, that works as a mechanism to carry out the maintenance of memories; and consequently, forming the foundation of learning and memory in the brain. (The weakening of synapse connections results in memory losses).

Former research had implied that an increase or decrease in synaptic plasticity for associative and non-associative memories would have the same properties, that is, both kinds of memories would either be maintained or lost if experimented with; that selective deletion would be impossible since it was considered that a single mechanism governs all the memories.

This hypothesis was tested by applying two different stimulations to two *sensory neurons connected to the same *motor neuron of Aplysia (one to induce an associative memory and another to induce a non-associative memory).

*Quick Fact:

Sensory neurons are those which sense and transfer signals from the outer parts of the body to the central nervous system.

Motor neurons are the ones that transmit signals from the central nervous system to the outer parts of the body.


The Inferences

When researchers began to determine the strength of the two connections mentioned above (in Aplysia), they noticed that both the stimuli caused an increase in strength of the synaptic connection. Further, they found out that this increase in strength was caused by a particular form of a protein molecule called PKM – Protein Kinase M. (PKM is a protein that is, in general, found to be involved in the formation and maintenance of a long-term memory).

However, there are two different forms of PKM involved in the two cases. For the associative memory, the PKM strengthening the connection was a type called PKM Apl III; and for the non-associative memory, it was PKM Apl I. This led to the discovery that any of these two memories could be erased by blocking the respective PKM molecule which took part in their strengthening, leaving the other untouched.

The researchers are hopeful that this study would help in comprehending the human memory as well since vertebrates and Aplysia have similar versions of PKM proteins.

In the words of Jiangyuan Hu, Ph.D., an associate research scientist in the Department of Psychiatry at CUMC and co-author of the paper, “Memory erasure has the potential to alleviate PTSD (Post Traumatic Stress Disorder) and anxiety disorders by removing the non-associative memory that causes the maladaptive physiological response. By isolating the exact molecules that maintain non-associative memory, we may be able to develop drugs that can treat anxiety without affecting the patient’s normal memory of past events.”

Dr. Schacher is of the opinion that this collective study will provide therapists with better ways to tackle trauma patients in the future, as they will be able to erase the non-associative memories by administering newly developed drugs.

For researchers to create or assign drugs that can weaken or erase non-associative memories, an extensive research on PKMs is still required.

Sources:

CUMC Newsroom
Current Biology