In joint research between the RIKEN Brain Science Institute in Japan and MIT, positive and negative memories were shown to interact in mood disorders and provided a specific brain circuit for future clinical interventions.
The , which was published in Nature, addresses the long-asked question of whether a positive memory can overwrite a negative one. To answer this question, the team of scientists used genetic engineering to create mice in which memory cells in an area of the brain, called the dentate gyrus (DG), could be tagged as memories are formed, and subsequently reactivated with an optical fiber that emits blue light and is implanted in the DG. The team would then be able to turn on memory cells created during the previous experiences.
To test the system, male mice were exposed to a positive experience (specifically, exposure to a female mouse) and a memory of the event was formed. Subsequently, they were exposed to a stressful situation that led to a state similar to depression. While they were depressed, lights were used to stimulate the DG of some mice and reactivate the cells from the positive experience. Surprisingly, the result was a robust recovery from depressed mood. Brain circuit mapping for this effect revealed two other brain areas that cooperate with the DG.
To learn whether this type of recovery from depression could include persistent changes in brain circuitry that are maintained even in the absence of light stimulation, the researchers provided chronic light therapy to the DG for 5 days, ensuring prolonged reactivation of the positive memory. . Mice receiving this therapy were resilient to the negative effects of stress-induced depression, suggesting that storing memories of positive experiences in the DG can be used to suppress or overwrite the harmful effects of stress on behavior, a new concept. in mood control.
These findings have important implications for the persistence of memories in coping with stress and depression. The interplay of positive and negative experiences and their corresponding memories is poorly understood, but the findings open the way to new therapy approaches in mood disorders that could be useful to patients in the future. The authors say it is too early to conclude that generally positive memories can mitigate the effects of stress-induced depression. However, it is clear that DG cells are promising targets for new therapeutic approaches regarding maladaptive mood states.
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