Remote fear memories of past traumatic events are permanently stored in the prefrontal cortex of the brain, a new study conducted by the University of California, Riverside, found.
Remote fear memory is intended to be a memory of a traumatic event that occurred months or decades ago. Neuroscientists have long known that the part of the brain responsible for storing recent fear memories is the hippocampus. Now, thanks to this recent study conducted on mice, they found that as memory matures with time, it becomes stored in the prefrontal cortex.
“It is the prefrontal memory circuits that are progressively strengthened after traumatic events and this strengthening plays a critical role in how fear memories mature into stabilized forms in the cerebral cortex for permanent storage,” said Jun-Hyeong Cho, co-author of the study.
In the research, mice received an "aversive stimulus"—usually an unpleasant occurrence that triggers a behavioural change—and associated it with a context. When mice were exposed to the same context a month later, they froze in fear, indicating that they could recall the remote memory. In addition, scientists also found that when the mice were exposed to the same context, but without the aversive stimulus, they were less scared.
“We found a small group of nerve cells or neurons within the PFC [prefrontal cortex], termed memory neurons, were active during the initial traumatic event and were reactivated during the recall of remote fear memory.”
“When we selectively inhibited these memory neurons in the PFC, it prevented the mice from recalling remote but not recent fear memories, suggesting the critical role of PFC memory neurons in the recall of remote fear memories,” said Dr Cho.
The recent study was published in Nature Neuroscience and was funded by grants from the National Institute of Mental Health. The implications of this discovery could in fact become a hallmark for the treatment of fear-related mental health disorders, such as PTSD.
“Considering that PTSD patients suffer from fear memories formed in the distant past, our study provides an important insight into developing therapeutic strategies to suppress chronic fear in PTSD patients,” Dr Cho stated.
PTSD is more common than people estimate: 70% of people will go through a traumatic event throughout their life, and 20% of those will develop PTSD. The National Institute of Mental Health states that this disorder can appear at any age, although it is more likely to affect war veterans, children, and people who have gone through a serious traumatic event, such as abuse or a disaster.
Now that the center of remote fear memories has been located, studies can focus on developing targeted treatments for PTSD-like disorders. Cho’s team, in particular, is planning to examine whether manipulating the prefrontal cortex will eliminate remote fear memories.
Photo credit: meo: https://www.pexels.com/photo/photo-of-head-bust-print-artwork-724994/
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