Why we can't seem to forget traumatic events

Washington, May 12 : Emotional memories of a traumatic episode in life often persist in our minds. Now, researchers from Switzerland claim that they have identified the molecular bases behind these strong memories.

The team led by Isabelle Mansuy, Professor of Cellular Neurobiology at ETH Zurich and of Molecular and Cognitive Neurosciences at the University of Zurich, has now shown that the enzyme calcineurin and the gene regulation factor Zif268 play a role in the signal processing of memories and learning.

These two decisively determine the intensity of emotional memories.

Calcineurin is a negative regulator of learning and memory, so its activity needs to be reduced to enable strong memorisation.

The generation of very persistent memories in the shortest possible time needs molecules in the brain that are not only activated rapidly but which also efficiently control the signalling pathways of long-term information storage in the brain.

The study was conducted using mouse model, as their learning processes are very similar to those in humans.

For the study, the researchers conditioned the mice to associate a sugar solution with nausea. This association persists for many months. The mice avoid the sugar solution during this period.

The researchers found that amygdala, a part of the brain, which is important for emotional perception, showed reduced activity of the enzyme calcineurin in conditioned mice compared to mice in which no association with nausea had been generated.

To understand the role of calcineurin in the memory process the researchers used transgenic mice in which they were able to selectively activate or deactivate the enzyme in nerve cells of the brain.

Inactivating calcineurin strengthened the memory of the association between sugar solution and nausea, whereas the memory was weakened by increased calcineurin activity.

The researchers were also able to demonstrate that the period of time needed to suppress the negative memory by a purely positive memory could be prolonged or shortened respectively by intervention.

"Emotional memories are not simply erased. Oppressive negative memories need to be actively replaced by positive memories," Science Daily quoted Mansuy, as saying.

She said that the negative memories do not disappear, they merely slide down in a kind of priority list and are outweighed by the newly learned positive memories.

"This process is not final and absolute, since the priority list can change again." Karsten Baumgartel, a post-doctoral researcher in Mansuy's group,

Baumgartel said that this is a big difference between emotional memories and learned knowledge.

"It is entirely possible for facts to vanish completely from the memory, whereas in extreme cases emotional recollections remain stored for a whole lifetime. Active intervention is necessary to reduce the priority level of negative memories," Baumgartel added.

We hope that our research has made a small contribution to enabling the same situation also to apply in the future to psychological traumas or brain diseases with memory weakness such as Alzheimer's, Parkinson's and strokes," said Mansuy.

ANI