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Post 3: Memory Engrams

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The complex yet multifunctional organization of systems in the brain allows us to use the same techniques and knowledge for seemingly distinct purpose. Papers published by Ramirez in 2013 and 2015 demonstrate this by using optogenetics to artificially activate memories in the hippocampus to determine whether false fear memories can be generated for a context in which there was no fear induction and to determine whether activation of positive memories can suppress depression and anxiety-related behaviors, respectively. Ramirez et al. (2015) were able to repurpose the techniques first used in their 2013 paper to investigate whether their techniques could be useful for reducing the behavioral effects of mood disorders.

One thing I am most curious about after reading these papers is how humans would experience reactivation of previous memories if this technique were adapted for humans for therapeutic purposes. In mice, we can measure only behavioral outcomes and physical changes in the brain, and behavioral results suggesting memories of the fear associated with foot shocks (Ramirez 2013) and of the happy state associated with positive memories (Ramirez 2015) are seen. However, in humans we can also assess thoughts and mental state; I would be interested to know whether artificial activation of neurons active in the dentate gyrus during a positive memory, for example, elicit the positive memory itself, or simply the positive emotions associated with it. While such an investigation is not ethically or logistically possible now, its results seem crucial to determine the breadth of influence such technologies could have for mood disorders and many other functions.

Another thing I found interesting about the Ramirez (2015) paper in particular was that there was distinction between anxiolytic behaviors and depressive behaviors, both in their classification in the methods and the results yielded. Often, anxiety and depression are grouped together in animal research, so it was interesting to see results that consistently showed depressive, but not anxiety-like behaviors, to be ameliorated by a technique. Such differentiation points to a possible way to specifically target depression.

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