Electrophysiology. is. Everywhere.

Electrophysiology can often be a mystifying area of research for anyone who is unfamiliar. I hope that the discussion of these two papers will be enlightening, as I myself still have gaps in my understanding of the methods. However confusing it may be, electrophysiology is a powerful tool for decoding specific circuitry within the brain. Both papers have used this technique to identify key populations of principle neurons and interneurons that play a role in fear conditioning and extinction. These methods heavily relied on mathematical analysis of ephys data to identify neurons as opposed to staining of cell types like many of the previous papers we have read. To me, this raises a question of which methodology is more reliable.

After reading the first paper by Herry et al (2008), I was left wishing that they had done a few more experiments. They determined that there were two populations of neurons controlling fear and extinction. Although they did a cFos study at one point in the paper to show which neurons were recently active, it did not appear that they did any sort of staining to identify what types of neurons these were. They could have stained for NeuN to identify principal neurons and somatostatin for GABAergic interneurons. These could have provided an added level of characterization of the neurons that they were examining if these markers were co-localized with the cFos. I found the second paper to be more comprehensive in its characterization of subgroups of neurons within the dmPFC-BA-hippocampus circuitry.

Another item that I felt was missing from this first paper was in terms of the behavior in the section "BA inactivation prevents behavioural transitions". They found that "inactivation of the BA before extinction training prevented the acquisition of extinction". I was wondering if there was any way for them to have shown that this effect is specific to fear learning. Perhaps they could have completed another behavioral test/ paradigm that would have shown that the animal's ability to learn at all was still intact after being exposed to muscimol.