How traumatic memories get hidden in brain

Scientists have discovered the mechanism in our brain that makes stressful or fear-related memories inaccessible.

The result could eventually lead to new treatments for patients with psychiatric disorders, the researchers said.

"The findings show there are multiple pathways to storage of fear-inducing memories, and we identified an important one for fear-related memories," said principal investigator professor Jelena Radulovic from Northwestern University.

Some stressful experiences - such as chronic childhood abuse - are so overwhelming and traumatic that the memories hide like a shadow in the brain.

A process known as state-dependent learning is believed to contribute to the formation of memories that are inaccessible to normal consciousness.

The best way to access the memories in this system is to return the brain to the same state of consciousness as when the memory was encoded.

Two amino acids, glutamate and gamma-aminobutyric acid (GABA), direct its emotional tides and control whether nerve cells are excited or calm.

However, scientists discovered another critical role -- these receptors also help encode memories of a fear-inducing event and then store them away, hidden from consciousness.

"The brain functions in different states, much like a radio operates at AM and FM frequency bands. It's as if the brain is normally tuned to FM stations to access memories, but needs to be tuned to AM stations to access subconscious memories," Radulovic said.

"If a traumatic event occurs when these extra-synaptic GABA receptors are activated, the memory of this event cannot be accessed unless these receptors are activated once again, essentially tuning the brain into the AM stations," the researcher said.

It is difficult for therapists to help these patients because the patients themselves can not remember their traumatic experiences that are the root cause of their symptoms.

"This could eventually lead to new treatments for patients with psychiatric disorders for whom conscious access to their traumatic memories is needed if they are to recover," Radulovic said.

The study was published in the journal Nature Neuroscience.