New study finds positive memories can reduce negative effects of work-related stress

The findings open a path to new mood disorder therapies

Recalling good memories of the past can reduce work-induced stress, a new study has found. Scientists found that artificial reactivation of memories stored during a positive experience can suppress the effects of stress-induced depression

The research, conducted by scientists at the RIKEN-MIT Center for Neural Circuit Genetics, shows how positive and negative memories interact in mood disorders, and provides a specific brain circuit for future clinical interventions.

The research 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 of the event was formed. 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. This resulted in a robust recovery from the depressed state, the researchers said. Mapping the brain circuit for this effect revealed two other brain areas — BLA and NAcc — that cooperate with the DG.

To examine whether this type of recovery from depression can include persistent changes in brain circuitry that remain even in the absence of light stimulation, the researchers supplied chronic light therapy to the DG over 5 days, ensuring sustained reactivation of the positive memories.

Mice that received this therapy were resilient to the negative effects of stress-induced depression, suggesting that memory storage of positive experiences in the DG can be used to suppress or overwrite the effects of stress on behaviours, a new concept in mood control.

The findings open a path to new approaches in mood disorder therapy that might be helpful for patients in the future, the researchers said.

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