Sunday, October 23, 2016

10/24 Herry et al. and Courtin et al.

            Herry et al. discovered that different groups of neurons in the BA are involved in fear learning and extinction. They used electrophysiology to isolate these different groups of neurons. When recording these neurons during extinction, they discovered that once extinction neurons began to increase in activity, fear neurons began to decrease one extinction block afterwards. After the neuronal changes, the behavioral changes began to occur; freezing began to decrease. The changes were measured with the change point analysis algorithm. I had never heard of the change point analysis algorithm before, and I thought it was an interesting approach to see if the neuronal changes actually corresponded with the behavioral changes. After fear renewal, extinction neurons were active 7 days after extinction. It would be interesting to test these neurons after a longer period of time to see if the activation of extinction neurons was more chronic. Also, after fear renewal, the extinction resistant neurons were not shown. I was curious why the authors chose not to show the data. Some additional data I would like to see is the raster plot for the rest of the experiments in the data set. It was present in the first figure but not for the rest of the experiments in the paper.

            Courtin et al. used an auditory fear conditioning paradigm that was similar to Herry et al., but used different techniques to look at populations of neurons. They recorded interneurons and principal neurons in the dmPFC that were responsive to CS+. The researches silenced type 2 (PVINs) interneurons using a cre-recombinase AAV. They were shown to have a large role in fear behavior. Optical silencing of PVINs by ChR2 before fear conditioning transiently induced freezing. The researchers also discovered that principal neurons (PNs) disinhibited during CS+ presentations preferentially targeted the BLA. This is because theta phase reseting by PVINs synchronizes PNs after CS+ presentations, and dmPFC PNs preferentially target the BLA to drive fear responses.

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