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Post 3: Ramirez et al. (2013 & 2015)

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            In the first paper published by Ramirez and collaborators, the researchers outlined how they created false memories in mice using fear conditioning. In brief summary, mice were taken off Dox and allowed to explore context A so that their cells could be labeled with ChR2-mCherry. After, the mice were put back on Dox and fear conditioned via shocks in context B while the cells labeled in context A were activated. When placed in either context A or a novel context C, it was shown that the mice froze significantly more in context A, not C, than background levels. This discovery of creating false memories artificially could give us insight into how humans form false memories. I’ve watched several videos of people falsely recalling what a criminal looks like based on external input. I’m also very curious about the psychological phenomenon of rosy retrospection – looking back at past experiences in a disproportionally positive manner. Does this same population of DG cells play a role in that? How do these false memories occur naturally?
            In Ramirez’s second paper, researchers explored an application of these memory circuits to try to suppress depression-like behavior. One of the main findings was that activating dentate gyrus cells that were labeled by a positive experience was able to reverse the effects of stress in the tail suspension test, sucrose preference test, and novelty-suppressed feeding test. The experiment that I found the most interesting was when the researchers explored the long-term rescue of depression-like behaviors. The five days of stimulation of positive memories lead to an increase in struggling in the tail suspension test and an increase in sucrose preference. However, the chronic activation did not ameliorate anxiety-related behaviors as measured by the open field test and elevated plus maze test. The paper speculates that this is due to the fact that the circuitry for these anxiety-related behaviors must be different. As discussed in class, everyone experiences depression differently, and there are many ways in which it can manifest. This difference in circuitry could explain why last week’s papers came to differing conclusions and why people do experience depression differently.

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