According to Jelena Radulovic, principal investigator and Dunbar Professor in Bipolar Disease at Northwestern University’s Feinberg School of Medicine, “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 turned to FM stations to access memories, but needs to be tuned to AM stations to access subconscious memories.”
She related that two amino acids that function as the “yin-and-yang” of the brain, glutamate and GABA, normally control the “tides” of emotions. However, the independent agent known as the extra-synaptic GABA receptor can itself change the state of the brain, from fatigued to sedate, drunk or psychotic. The extra-synaptic GABA receptors also encode the memories of events that are scary or stressful.
As Radulovic explained, “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.”
In mouse experiments used to test the chemical pathway, the researchers infused the mice hippocampuses with gaboxadol, a drug that stimulates the receptors. When the mice were put in a box and shocked, they showed fear. The next day, when they were put in the box without the drug, they moved around without remembering the shock. When they were given the drug and put in the box again, they froze in place.
“It’s an entirely different system even at the genetic and molecular level than the one that encodes normal memories,” said Vladimir Jovasevic, the lead author and a postdoctoral researcher at Northwestern at the time of the work.
The entire system is governed by a micro RNA known as miR-33 – and could be the brain’s protective mechanism, they added.
“State-dependent learning” is a theory that memory formed in a particular mood can best be recalled when the brain is back in the same state – whether that is aroused, drugged, happy or sad, according to experts. A British study of the phenomenon published in 1997 found that recall was superior, based solely on the emotional mood of the subjects.
Researchers debate the use of repressed memories because of its importance as evidence of childhood abuse and other traumatic experiences. A 2001 study published in Applied Cognitive Psychology (https://onlinelibrary.wiley.com/doi/10.1002/acp.766/abstract) found that traumatic memories were special and differentiated from normal memories, but did not find a pathway to create those memories.