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Positive memories can help to cope with stress-induced depression

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Posted June 19, 2015

We have already written that paying more attention to angry faces can lead to a greater risk of getting depression later in life. Now we have to write about a way to reduce such risk. Scientists at RIKEN-MIT Center for Neural Circuit Genetics have showed that artificial reactivation of memories stored during a positive experience can suppress the effects of stress-induced depression. In other words, recalling nice memories may reverse depression.

Positive emotions. Image credit: geralt via Pixabay, CC0 Public Domain

Positive emotions. Image credit: geralt via Pixabay, CC0 Public Domain

The researchers have conducted this study in order to tackle a question that has been puzzling scientists for a long time – can a positive memory overwrite a negative one. Team had to use genetic engineering to figure it out. They created mice, in which memory cells from a brain area called the dentate gyrus could be tagged while memories formed, and later reactivated with a blue light-emitting optical fibre implanted in that particular brain area. Using such setup, scientists were able to turn on memory cells created during previous experiences.

“Depressed mouse”, after “Sorrowing Old Man” by Van Gogh. Experiments with mice provided good knowledge about brain circuits involved in recalling positive experiences and depressive state of mind. Image source: riken.jp (Tonegawa Lab/Julian Wong)

“Depressed mouse”, after “Sorrowing Old Man” by Van Gogh. Experiments with mice provided good knowledge about brain circuits involved in recalling positive experiences and depressive state of mind. Image source: riken.jp (Tonegawa Lab/Julian Wong)

Then scientists had to create such positive experience that mice could remember. They relied on simple things. Male mice were exposed to a female mouse and formed a memory of the event. Later scientists had to put mice into stressful environment to induce a depression-like state. Because of properties created during genetic engineering, the researchers could use light to stimulate the dentate gyrus to reactivate the memory cells for the positive experience. This simple experiment resulted in a quick and stable recovery from a depressive state. Scientists also wanted to get a specific brain circuit for future clinical interventions.

The researchers found that two other brain areas, called the BLA and NAcc, cooperate with the dentate gyrus the brain circuit for such effect. This is important knowledge, seeking to create new therapies to treat depression. That is why scientists wanted to know whether this type of recovery from depression can include persistent changes in brain circuitry that remain even in the absence of light stimulation.

They continued the light therapy for over 5 days, ensuring sustained reactivation of the positive memories. These mice who received this therapy quickly recovered from the negative effects of stress-induced depression, which suggests that memory storage of positive experiences in the dentate gyrus can be used to suppress or even overwrite the damaging effects of stress on behaviour.

Despite decades of behavioural studies and advancements in science of psychology, the interaction of positive and negative experiences and their corresponding memories is still poorly understood. These new findings, however, open a path for new approaches to treat mood disorders in the future. Scientists still cannot say for sure if positive memories in general can mitigate the effects of stressful depression, but the dentate gyrus brain cells already look like promising targets for new therapeutic approaches to treat such maladaptive mood states.

Depression is not just a sad mood. It is a mental disorder that may even claim lives of those who suffer from it. Stress induced depression is not a rare feature of our contemporary lifestyle as stress became integral part of our rapid everyday life. That is why scientific discoveries that are seeking to treat depression are always greeted with excitement and hope.

Source: Riken

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