Washington, June 18 (IANS): Revealing the curative power of memory, scientists have established that artificial reactivation of memories stored during a positive experience can suppress the effects of stress-induced depression.

The research, published in the journal Nature, shows how positive and negative memories interact in mood disorders and provides a specific brain circuit for future clinical interventions.

The study tackles the long-standing question of whether a positive memory can overwrite a negative one.

"The interaction of positive and negative experiences and their corresponding memories is poorly understood but the findings open a path to new approaches in mood disorder therapy that might be helpful for patients in the future," said Susumu Tonegawa, professor at the Massachusetts Institute of Technology, who received the 1987 Nobel Prize for Medicine for his discovery of the genetic mechanism that produces antibody diversity.

The team used genetic engineering to create mice in which memory cells from a brain area called the dentate gyrus (DG) could be tagged while memories formed and later reactivated with a blue light-emitting optical fibre implanted in the DG.

The team could then turn on memory cells created during previous experiences.

To test the system, male mice were given a positive experience -- exposure to a female mouse -- and a memory formed of the event.

They were then exposed to a stressful experience that led to a depression-like state.

While they were depressed, light was used to stimulate the DG of some mice and reactivate the memory cells for the positive experience.

Surprisingly, this resulted in a robust recovery from the depressed state.

The results have important implications for the persistence of memory in coping with stress and depression.

"It is too early to conclude whether positive memories in general can mitigate the effects of stressful depression. However, it is clear that DG cells are promising targets for therapeutic approaches to maladaptive mood states."