Courtesy of PexelsFear is deeply ingrained in our memory. We associate bad memories with fear and condition ourselves into being afraid of the potential outcomes. The University of California, Riverside conducted a study in which they demonstrate how remote fear memories formed in the distant past are permanently stored in our brains. The subject of these studies? Mice.

Contextual memory is the basic process in long term memory which allows us to remember the circumstances of an event. These circumstances involve but aren’t limited to the five senses, emotions, and social situations. Their formations are made possible by hippocampal circuits. The progressive and synapse-specific strengthening of the prefrontal cortex (PFC) circuits can ensure that these memories can be stored in the long term, and the standard model suggests that long term storage involves synaptic changes, whose substrates have not been identified yet. 

Studies from some time ago suggest that the neurons in the medial prefrontal cortex (mPFC) and the anterior cingulate cortex (ACC) play a role in preserving these contextual memories, but only of the remote variety. The PFC memory engram neurons are created during learning and mature over time, and then are reactivated during remote memory recall. They are not very well understood, and scientists are still trying to figure out if and how the synaptic strength of neocortical circuits change during consolidation.

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A study of mice showed that during contextual fear conditioning (CFC) certain neurons activate inside the mice’s brain and that they would then associate the situation and context they were just in with aversive unconditioned stimuli. After CFC exposure, the mice showed freezing behavior, and it was noted that certain neurons were more active during that certain memory recall. The results of the study suggest that certain mPFC neurons that were active during CFC were reactivated during recall, which caused the neurons to stimulate memory recall, thus sending the mice into a state of fear.

Overall through the studies that were conducted for this research a few conclusions can be drawn out. The first being that system consolidation strengthens the mPFC circuit whereas memory extinction weakens it. And the other that the retrieval of remote contextual fear memory can be suppressed by preventing a certain group of mPFC neurons from firing up. From the later conclusion it is suggested that by doing so it can be used to potentially treat chronic maladaptive fear memory in PTSD.