Ramirez et al. (2013) and Yiu et al. (2014)

Ramirez et al. (2013) addressed what I think is a very interesting topic: can memories be artificially manipulated?  They used optogenetics to create false fear memory in the hippocampi of mice.  They compared the behavior of these mice to those that underwent regular fear conditioning.  The researchers narrowed their investigation to the dentate gyrus neurons that were activated while the mouse was in the first novel environment.  While undergoing fear conditioning in a second novel environment, these neurons were artificially reactivated.  When the mouse was placed in the first environment again, it reacted with more fear than the first time it was in there, thereby supporting that Ramirez et al. (2013) were able to implant false fear memory into the mouse.

Yiu et al. (2014) studied neurons in the amygdala rather than in the hippocampus.  I think that it would have been good if Ramirez et al. (2013) also tested how artificially activating lateral amygdala cells would have affected fear memory, just to see the difference.  According to Yiu et al. (2014), each memory activates its own memory trace, and therefore, the same particular group of cells.  Yiu et al. (2014) showed that neurons do have a biochemical specificity for which cells become part of a memory trace or not.  Those that express more neuronal excitability, as increased by CREB, are more likely to be allocated to the engram.  Also, CREB excites the cell only during fear memory formation as shown by how neurons with CREB that were not conditioned did not show a fear response to the tone.  I think that Yiu et al. (2014) should really explore more about how these engrams are related to each other.  Are they all interconnected or are some segregated?  Is the engram changed if the allocation process is prevented?  They should also look into how increasing CREB between memory traces might link or uncouple memories.

Falsifying memory is another representation for PTSD in a way because many fear symptoms still plague people who are not even experiencing the source of that fear anymore.  It is important to study the basis of how false memories are formed in order to possibly reverse the emotional symptoms they cause.  Understanding the connection between engrams would probably be very applicable to schizophrenia considering how that condition is characterized by inappropriate associations.