Distant Memories of Fear Lurk in Your Brain, And We May Have Found Their Hiding Place : ScienceAlert

Memories of traumatic events can continue to resurface in the brain long after the moment has passed, leading to conditions such as post-traumatic stress disorder (PTSD).

While it is clear that an area of ​​the brain called the hippocampus plays a central role in memory formation, the physical nature of long-term fear storage as a “remote memory” has remained elusive.

In a new study on mice, scientists from the University of California, Riverside, in the US, have described some of the key mechanisms through which distant fear memories are consolidated and identified the physical embodiment of distant fear in a prominent part of our brain. .

By understanding more about how these traumatic flashbacks are embedded, we may be able to improve therapies and treatments for those who suffer them.

The researchers used mice engineered with nerve cells that could be easily identified during fear responses, along with a mixture of viruses that cut important neural pathways thought to be involved in memory consolidation, or helped identify key connections between neurons. .

An electric shock served as a fear memory event for the transgenic mice. When the test subjects returned to the shock site a month later, they froze, indicating that distant fear memories stored somewhere in the brain were indeed being recalled.

Looking closely at different brain samples revealed a steady strengthening of connections within a small group of memory neurons in what is known as the prefrontal cortex (PFC) – an area responsible for decision-making and cognitive behavior.

Fear memory neurons in red among other prefrontal cortex neurons in blue. (Cho Lab/UCR)

Further tests showed that when these special memory neurons were severed, the mice were unable to recall the distant fear while still retaining the recent trauma. In other words, PFC memory neurons form the physical structures, or engrams, for distant fear memories.

The rats were then exposed to the same locations, but this time without an aversive stimulus. This was sufficient to reduce the fear response and alter the circuitry of these neurons associated with the traumatic event, the researchers demonstrated.

“It is 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,” says neuroscientist Jun-Hyeong Cho.

“Using a similar mechanism, other distant non-fearful memories can also be permanently stored in the PFC.”

There is more work to be done to look more closely at these mechanisms. The researchers plan to see if a selective weakening of PFC memory circuits will suppress recall of remote fear memories, which could then inform treatments in humans.

“Interestingly, the extinction of the remote fear memory weakened the prefrontal memory circuits that had previously been strengthened to maintain the remote fear memory,” says Cho.

“Furthermore, other manipulations that blocked the strengthening of PFC memory circuits also prevented remote fear memory retrieval.”

About 6 percent of the American population is expected to experience some form of PTSD in their lifetime, and knowing how these memories are stored and then retrieved will be crucial to understanding how to treat individuals with fear and anxiety-based disorders. in trauma.

The research is published in Nature Neuroscience.