Lost memories and Alzhemiers

    In September of 2025, Stephanie Grella, a neuroscience faculty member at Loyola University Chicago, gave a talk about engrams and her research relating to engrams. One of the types of engrams she spoke about was silent engrams, which are memories that are formed but can't be retrieved. Another type is dormant engrams, which are memories that are formed but forgotten until a cue is presented. She spoke about Alzheimer's disease and how memories that are supposedly destroyed by Alzheimer's disease could actually still be there. These memories could be brought back from artificial stimuli, triggering the memory. 

    "Memory engram stability and flexibility" by Zaki and Cai, they looked through former literature on the encoding, consolidation, and recalling of episodic-like memory (Zaki & Cai, 2025). In one of the articles they reviewed, it was showcased how false long-term memories can be artificially created in mice by stimulating their neural circuits that represent conditions and unconditioned stimuli. They also spoke about how DNA repair pathways can help with learning, therefore also helping with strengthening memory. 

    "Optogenetic stimulation of dentate gyrus engrams restores memory in Alzheimer's disease mice" by Perusini et al. is another article that explores engrams and how they relate to Alzheimer's disease. In this article, the researchers utilize optogenetics and rat models that have Alzheimer's symptoms to determine if stimulating the dentate gyrus can treat memory loss. Through their research, they were able to find that optogenetics is a promising method that could be used to treat memory loss. They also found that within the mouse they were researching, some created false memories, which is known to be a symptom of Alzheimer's disease. Optogenetics was able to help with this. 

    

    These articles, along with Dr. Grella's talk, profoundly showcase the amount of research that still needs to be done when it comes to memory. It is very clear why memory is such a hard thing to understand and study; studies on memory loss can either be done on animals or with humans who already have a brain lesion (ex, patient H.M.). This makes it more difficult to understand how memory could be functioning in humans with healthy brains. While optogenetics can be used to treat memory loss, it is an invasive treatment. Much work still needs to be done to find a solution to the memory loss with non-invasive methods. I find memory research to be very important, not just because it is nice to always have our memories, but also because of the emotional impact it has on the people around us.

References:

Perusini, J. N., Cajigas, S. A., Cohensedgh, O., Lim, S. C., Pavlova, I. P., Donaldson, Z. R., & Denny, C. A. (2017). Optogenetic stimulation of dentate gyrus engrams restores memory in Alzheimer’s disease mice. Hippocampus, 27(10), 1110–1122. https://doi.org/10.1002/hipo.22756

Zaki, Y., & Cai, D. J. (2024). Memory engram stability and flexibility. Neuropsychopharmacology, 50(1), 285–293. https://doi.org/10.1038/s41386-024-01979-z