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).

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

In a new mouse study, scientists from the University of California, Riverside, USA, have described some of the key mechanisms by which remote fear memories are consolidated and identified the physical embodiment of fears at distance in an important part of our brain.

By better understanding how these traumatic flashbacks fit in, we may be able to improve therapies and treatments for those who suffer from them.

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

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

Careful examination of various brain samples revealed a steady strengthening of connections within a small cluster of memory neurons in what’s called the prefrontal cortex (PFC) – an area responsible for decision-making and cognitive behavior.

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

Further tests showed that when these particular memory neurons were severed, the mice were unable to remember distant fears, while remembering more recent trauma. In other words, the PFC memory neurons form the physical structures, or engramsfor remote fear memories.

The mice were then exposed to the same locations but this time without the aversive stimulus. This was enough to reduce the fear response and change the circuitry of these neurons in relation to the traumatic event, the researchers demonstrated.

“It is the prefrontal memory circuits that are progressively reinforced after traumatic events and this reinforcement 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 fearless remote memories could also be permanently stored in the PFC.”

There is still work to be done to examine these mechanisms more closely. The researchers plan to see if selective impairment of PFC memory circuitry will suppress remote fear memory recall, which could then inform treatments in people.

“Interestingly, the extinction of remote fear memory weakened prefrontal memory circuitry that was previously enhanced to store remote fear memory,” Cho says.

“Furthermore, other manipulations that blocked reinforcement of PFC memory circuitry also prevented remote fear memory recall.”

About 6% of the US population is expected to suffer from some form of PTSD in their lifetime, and knowing how these memories are stored and then brought back will be crucial in determining how to treat people with fear-related disorders. and trauma.

The research has been published in Natural neuroscience.

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