Navigating Through the Engrams

In the first talk of the semester, Loyola's very own neuroscience faculty member, Dr. Stephanie Grella, presented a talk about engrams and their navigation through synaptic and neural connectivity. Engrams are described as the "footprint" of memory retention and storage. They undergo continuous chemical and physical changes to strengthen their synaptic connectivity every time you try to retrieve and reconstruct a memory. In one of the studies in the research paper that we had to read before the seminar, they wanted to evaluate how important synaptic activity is in memory retrieval, secondly, how studies support the existence of engrams in learning while inducing long-lasting not only synaptic but also cellular modifications, thirdly, how the loss and gain of function shows that engram cells can retrieve "lost memory", and lastly how an artificial engram can guide behavior (Josselyn & Tonegawa, 2020). This shows that engrams can eventually retrieve certain memories that were "lost" if given internal cues; a memory always comes back.  

In the article by Tomas J. Ryan and colleagues, "Engram Cell Connectivity: An Evolving Substrate for Information Storage," they discuss how not only is the brain capable of retaining new information, but also how the brain changes based on the information that we are first introduced to. A study in this article is the engram labelling technology, which helps identify and manipulate certain engrams and neurons that store a particular memory (Ryan et al., 2021). In the experiment, they used mice and an internal cue by shocking the brain of the mice; they were able to distinguish the different parts of the brain that are used to recruit their connectivity and engrams. After the tagging of the engram is established, they use a Green Fluorescent Protein (GFP). With this type of technology, they were able to manipulate engrams in vivo, a technique known as Optogenetics. Optogenetics has helped us control the activity of certain neurons and how they influence behavior and learning. Now that the mice are used to being shocked, that certain cue will activate a behavioral response, which will create a new pathway in the brain, forming new connections between the cells. 

When comparing the article with Dr. Stephanie Grella's talk, both explain and reinforce the idea that when engrams are being influenced by certain cues, the brain can manipulate its connectivity to retain the new information, but also remember the old memories from past experiences. I found it very interesting how our brain can change and manipulate itself to a certain extent to influence our behavior and our learning based on the brain's wiring and its connectivity. Memories are never forgotten but rather stored in the brain until a cue and/or stimulus is presented that triggers the brain and brings back that "lost" memory. 

 

References

Josselyn, S. A., & Tonegawa, S. (2020). Memory engrams: Recalling the past and imagining the future. Science, 367(6473). https://doi.org/10.1126/science.aaw4325

Ryan, T. J., Ortega-de San Luis, C., Pezzoli, M., & Sen, S. (2021). Engram cell connectivity: an evolving substrate for information storage. Current Opinion in Neurobiology, 67, 215–225. https://doi.org/10.1016/j.conb.2021.01.006
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