10/24 fear papers

This week’s papers further discussed fear expression and expanded on the topic by performing experiments revolving around switching it on and off by neuronal circuits and how some PVIN interneurons shape activity to drive fear expression.

The Courtin et al. 2014 paper in particular left me with a few questions. First of all, they kind of lost me when they started discussing theta phase resetting and oscillations in Figure 4 and Figure 5. Maybe it’s just my lack of knowledge in that particular subject matter, but I feel like they could have introduced it and discussed it better since it appears to be a vital aspect of their experiments. If they just touched upon the basics then that would have made it a lot easier for readers like me to follow.

In that same paper, I was a bit confused on Figure 2d. They stimulated PVINs via ChR2, which would ultimately inhibit freezing since PVINs (such as Type 2 PVINs) are inhibited during freezing. The results show that there was a “significant” decrease in freezing in mice injected with ChR2 over the GFP control mice, which makes sense, but in those ChR2 mice, there was still a 60% freezing rate (in the Post FC graph). Not to mention, when you shine no light (thus you do not see effects of ChR2), it’s still about a 60% freezing rate. When you compare that number to Figure 3c, in which PVINs were stimulated with the inhibiting ArchT which would increase freezing, the numbers aren’t too far off. I would have liked to see, however, another graph in Figure 3c showing Post FC (like in Figure 3d) to have a better comparison.