Distant memories of fear lurk in your brain, and we may have found their hiding place: ScienceAlert

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

While there is a clear 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 a ‘remote memory’ remained elusive.

In a new study in mice, scientists from the University of California, Riverside, in the US, described some of the key mechanisms by which remote fear memories are consolidated and identified the physical embodiment of remote fears 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 from them.

The researchers used mice engineered with nerve cells that could be easily identified during the fear response, 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.

Electric shock served as a fear memory event in transgenic mice. When the test subjects returned to the shock site a month later, they froze, indicating that remote fear memories stored somewhere in the brain had indeed been recalled.

Close observation of 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.

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

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 relevant to the traumatic event, the researchers showed.

“It is the prefrontal memory circuits that progressively strengthen after traumatic events, and this strengthening plays a key 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 memories unrelated to fear 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 selectively weakening the PFC memory circuits will suppress the recall of remote fear memories, which could then affect treatment in humans.

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

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

About 6 percent The US population is expected to experience some form of PTSD in their lifetimes, and knowing how these memories are stored and then retrieved will be crucial in figuring out how to treat individuals with fear and trauma-based disorders.

The research was published in The neuroscience of nature.