week 5

I’m glad I’m not the only one to say this, but like many others, I found the paper by Courtin et al (2013) extremely difficult to follow simply because they addressed various subtypes of neurons, their correlation with freezing, and various oscillation procedures that I am not familiar with. Even though I spent a lot of time trying to dissect and make sense of the paper, I still feel completely lost. Because of this limitation, I was not able to fully understand the depth of research or the take home message associated with it. Hopefully, after tomorrow’s discussion that won’t be the case.

Compared to the 2013 paper, Herry et al (2008) was much easier to follow as their approach was simplistic and I am familiar with the concepts of fear conditioning and extinction. Additionally, their experiments seemed to have a logical flow and seemed to build off each other, which makes it easier to understand. It was interesting to learn about the distinct types of neurons (fear and extinction neurons) and how they represent functionally different classes that have the ability to distinguish between the contexts the animal is in. I also found the concept of emotional perseveration to be quite cool – wish they had more to say about it. Having said that, I was not fully convinced with some of the conclusions made in the paper. For example, in the section titled “rapid reversal of activity during fear renewal’’, the authors found that - After successful recall of extinction memory (Fig. 4b), mice were transferred to the context in which they had been initially fear conditioned. Changing context resulted in a modest, but significant, increase in baseline freezing levels owing to contextual fear conditioning (Supplementary Fig. 3), and in a full renewal of the original cued fear memory. I was a little confused after reading this because isn’t fear extinction carried out in the same context as the one in which the animal was fear conditioned in? So why would they carry out extinction in a different context? Another point in the paper that left me puzzled was - Comparing the averaged time courses of CS-evoked activity of fear and extinction neurons during the acquisition of behavioural extinction indicated that significant behavioural changes occurred after the activity scores of the two populations of neurons crossed over. What do they mean by “crossed over”?