Week 5: Herry and Courtin

This week, I started by reading the Herry paper, which identified distinct fear and extinction neurons in the BLA. I was most interested by the findings summarized in figure 3, where researchers were able to outline the order of the events leading up to extinction: extinction neuron activity increasing, followed by fear neuron activity decreasing, followed by visible behavioral changes (decreased freezing). I think it would have been interesting if researchers used the methods to take the findings in figure 4 a step further, and analyze the sequence of events during fear renewal as well. Overall, I think the order of experiments made a lot of sense and they all tied together really nicely, with the exception of figure 6, which felt a bit out of place to me. It seems like a great starting point for a completely new paper. In that case, I would be more interested in seeing how targeted inhibition of either fear or extinction neurons at various points throughout the experiment would affect fear conditioning, extinction recall, or fear renewal. I am curious about the location of these two distinct neuronal populations in the BLA (are they clustered together or evenly distributed?). Finally, I would love to see how activity of these neurons deviates from the norm in PTSD patients. Are their extinction neurons less active, are their fear neurons more active, is it a combination of the two, is it circuitry damage between these neurons and the brain regions they communicate with, or something else entirely?

The Courtin paper was far more challenging for me, mostly due to my initial unfamiliarity with the significance of theta firing and the importance of neuronal synchronization. While I did eventually come to understand their findings, I am still a bit perplexed about the importance of synchronized neuronal firing. I wish we could have seen some side-by-side data of theta phase resetting and freezing behavior. Specifically, I would have liked to see how turning the light responsible for the inhibition of PVIN on and off would impact freezing behavior in a fear conditioned mouse (in figure 4).