Week 4: Herry (2008) and Reznikov (2015)

Both papers this week discussed fear and extinction training. Herry et al. (2008) focused on learning more about the pathways involved in these processes. This paper looked at differential fear and extinction neurons in the BA, and examined how these neurons have both specialized functions and unique pathways that contribute to fear conditioning and extinction training. Reznikov et al. (2015) focused on demonstrating the strengths of a new animal model for PTSD.

I thought that Herry et al. (2008) was a very interesting paper, in that it showed that there are specialized neurons in the BA that are responsible for fear and extinction learning. Fear neurons in the BA are activated during and after fear conditioning, while extinction neurons are silenced. After extinction training, however, extinction neurons begin to activate. One part of this that I thought was especially fascinating was that there is a sort of delay in the inactivation of fear neurons. When going through extinction training, the activity of extinction neurons increases, before fear neurons decline. The change in behavior follows this change in neuronal activity. This explains why consolidation periods are sometimes necessary to see changes in behavior after extinction training.

This idea really stuck out to me when I was reading Reznikov et al. (2015), in which the rats were given one day of fear conditioning and then just one day of extinction training (without anytime to consolidate this learning). After this, they were separated into weak-extinction and strong-extinction groups. Based on the findings of Herry et al. (2008), perhaps the weak-extinction rats were simply not yet able to demonstrate the behavioral effects of the extinction training since they did not have a chance to consolidate their learning. We know that the behavioral effects follow the change in neuronal activity, so perhaps the weak-extinction rats have a slower reversal of neuronal circuitry (activating extinction neurons and turning off fear neurons), and therefore the behavioral changes are delayed. This could be a possible reason for why some rats (and potentially people), are more prone to developing PTSD.  
 

I think that it would be interesting to use the model proposed by Reznikov et al. (2015), and look at the differential activation of fear neurons and extinction neurons in both the weak-extinction and strong-extinction animals. I think that it would be interesting to see if certain animals are more prone to having slower/delayed changes in neuronal activity, and to see if this could be a factor in the development of PTSD.