Week V

          I found this week’s set of papers quite difficult to understand, particularly Courtin et al. I am not familiar with electrophysiology so when the researchers were talking about theta waves and theta wave resetting I did not know what that meant. I was not sure if theta waves were specific to fear circuits or if they had any unique significance to the research question being asked. Regarding theta wave resetting, reading the text alone was insufficient for my comprehension. My first impression was that theta wave resetting had something to do with the presentation of the conditioned stimulus causing the neurons to reset their firing pattern and ultimately cause the neurons to start firing synchronously. This assumption was validated when looking at the LFP traces in Figure 4. The overall message the results in Figure 4 are trying to convey is that when the mice heard the CS+ tone their neurons began firing synchronously compared to when they heard the unpaired tone and their neurons continued to fire asynchronously.

As a side not, I also thought it was interesting that it is the inhibition of PVINs that induces theta phase resetting rather than the activation. Generally speaking, I found the fact that Type II INs  (PVINs) inhibit PNs and that it is the disinhibition of PNs that results in the animals freezing.

I really liked how the Courtin et. al paper was organized. I felt like each experiment built on the results of the previous one and formed a sort of narrative that once understood was relatively easy to follow. For example, the researchers first identified two types of populations of neurons in the dmPFC, putative PNs and INs. The researchers hypothesized that Type II INs were PVINs and so the next experiment set out to discover if they were correct. Once the researchers confirmed Type II INs were indeed PVINs they wanted to know if the inhibition of PVINs caused fear expression. Each successive experiment proceeded in a similar pattern of the next one building off of the conclusions reached from the previous one. I believe the researchers were successful based on their experiments and their results in their findings that persistent fear behavior is modulated by specific prefrontal inhibitory circuits.