Synapse-specific plasticity governs identity overlapping memory traces

on 27 July 2018
A study of anxiety by memory

Anxiety, as a disorder, and its many types of behaviour are progressive by nature and seemingly store traces of similar memories of separate but similar events . . . 

The brain works on algorithmic processes!

Anxiety is best described as the anticipation of danger, be it in a minute or a year. Its purpose is to prepare us for the unknown but expected arrival of danger. It does this by initiating the fear response (fight or flight); seemingly putting us ahead of the curve! However, it is useful to look at fear in two ways: 1) the activation of the fear response by the detection of fear-related stimulus and 2) the conscious awareness of the feelings we know as fear. The brain/mind can detect and respond to fear totally outside of our awareness, we can detect something and initiate an evasive action with no awareness of fear. However, upon reflection, the awareness of the danger we were in can retrospectively stimulate feelings of fear. The system that detects and responds to a fear stimulus is separate from the one that creates the feeling we call fear (Joseph LeDoux - Anxious 2015).

This research is interesting because it moves us closer to finding alternative solutions to anxiety disorders. In the meantime, hypnotherapy, as an alternative to mainstream medicine, provides sufferers of anxiety with an exceptional opportunity to combat this deleterious condition. How it does that is by creating alternative memory traces, which are most likely akin to the effects related to retrograde amnesia in this study?

As a solution to unwarranted and unnecessary anxiety, hypnotherapy offers sufferers respite in the short term, leading to more permanent healing over time. Why is this important? It's because anxiety-type behaviours are linked to survival responses and, as such, the habits they form are not so easily let go. The respite gives the brain/mind time to adjust and eventually to form new behavioural responses. In some sense it's similar to having stitches to a deep wound, the stitches create a temporary situation that allows the wound to heal, much more quickly than without the stitches. Hypnotherapy creates the equivalent of mental stitches that allow the brain/mind to effect a slightly more permanent solution. Slightly more permanent solution? Yes, anxiety is an important facet of everyday life and we cannot totally eliminate it. In that sense, another anxiety type disorder could develop again in the future but it would not necessarily be the return of the older, treated, condition, merely a newer and, more likely than not, different condition; albeit the feelings would likely feel the same!

My objective here is to help people understand how and why we become illogically trapped into emotional experiences that may actually be happening but for reasons different to what we would imagine! If you want to know more about how Hypnotherapy why not make an appointment for a Free Consultation?

For more information on the Free Consultation - Go Here Or, to book your Free Consultation today, you can do so here

The Research: 

Memories are formed through long-term changes in synaptic efficacy, a process known as synaptic plasticity, and are stored in the brain in specific neuronal ensembles called engram cells, which are activated during corresponding events. When two memories are associated, cell ensembles corresponding to each memory overlap. However, each memory has its own identity. How the brain stores and defines a specific memory identity when two memories interact and are encoded in the shared ensemble was elusive. Here, a research team led by Dr Kaoru Inokuchi at the University of Toyama shows that synapse-specific plasticity represents specific memory entities, and that synaptic plasticity between specific engram assemblies is both sufficient and crucial for information storage.

We exposed mice to auditory fear conditioning, in which a tone was associated with a foot shock. Synaptic plasticity between the auditory cortex (AC) and the medial part of medial geniculate nucleus (MGm) neuron terminals and the lateral amygdala (LA) neurons mediates this association. After complete retrograde amnesia, optogenetic stimulation of the activated ensemble terminals of the AC and the MGm in the LA failed to induce fear memory recall, indicating that the memory engram no longer existed in that circuit. This result was correlated with the resetting of synaptic strength and functional connectivity between engram assemblies.

Next, mice were fear conditioned to two different tones, separated by 5 hours. Therefore, the two memory traces interacted and overlapped in LA. Complete retrograde amnesia of a given fear memory did not affect the linked fear memory encoded in the shared ensemble, indicating that memories are stored in specific synapses.

Then, we addressed the question of how each memory reserves its individual identity within the shared ensemble. We used optical long-term depression (LTD) to depotentiate the synaptic efficacy in synapses specific for certain memory. Depotentiation of the plasticity at synapses specific to one memory deconstructed the specific connectivity between engram assemblies, thereby affected the recall of only that memory without influencing the linked memory in the same population of neurons. Thus, sharing of engram cells underlies the linkage between memories, while synapse-specific plasticity guarantees the identity and storage of individual memories.

Our findings demonstrate that synapse-specific plasticity is necessary and sufficient for associative fear memory storage, and it guarantees uniqueness to the memory trace, advocating the plasticity as a substrate for the fear memory engram. Furthermore, we achieved selective and total erasure of fear memory from an engram network without affecting other memories stored in the shared ensemble by resetting the plasticity in a synapse-specific manner. This leads to a better understanding of the mechanisms underlying memory storage and may give insight into therapeutic ways to treat post-traumatic stress disorder.

Story Source:

Materials provided by the Japan Science and Technology AgencyNote: Content may be edited for style and length.

Journal Reference:

  1. Kareem Abdou, Mohammad Shehata, Kiriko Choko, Hirofumi Nishizono, Mina Matsuo, Shin-ichi Muramatsu, Kaoru Inokuchi. Synapse-specific representation of the identity of overlapping memory engramsScience, 2018; 360 (6394): 1227 DOI: 10.1126/science.aat3810