The strongest memories are created by very rewarding and demanding experiences, new research reveals.
However, we make these memories still stronger by replaying them repeatedly in our minds.
Each time a memory is recalled and re-lived, the neuronal activity that sustains it is strengthened.
This means that we actually edit our memories by what we choose to recall and replay.
Keep running over distressing incidents and these become stronger.
Remembering happier times, though, makes these memories stronger.
Most people (but not all) have a tendency to forget the negative and replay the positive.
This bias is sometimes called ‘the psychological immune system’.
Our minds ‘fight off’ negative memories automatically to leave us feeling happier — or at least, that is the theory.
Professor Fabian Kloosterman, study co-author, said:
“One of the ways in which our brains consolidate memories is by mentally reliving the experience.
In biological terms, this boils down to the reactivation or replay of the neuronal activity patterns associated with a certain experience.
This replay occurs in hippocampal-cortical brain networks during rest or sleep.”
For the study, rats were trained to remember where food was located in a maze.
Mr Frédéric Michon, the study’s first author, explained the results:
“Perhaps unsurprisingly, we found that rats remembered better the location where they found the large reward.
But we also observed that this reward-related effect on memory was strongest when the food pellets were located in places that required more complex memory formation.”
The scientists then disrupted the rats’ memories before they could be consolidated.
This is the human equivalent to winning the lottery, but never thinking about it again.
The effect was to impair the rats’ memory.
If they couldn’t replay the memory to themselves about where the food pellet was, they found it harder to remember.
Professor Kloosterman said:
“Our results demonstrate that replay contributes to the finely tuned selective consolidation of memories.
Such insights could open future opportunities for treatments that help to strengthen memories, and could also help us understand memory decline in diseases such as dementia.”
The study was published in the journal Current Biology (Michon et al., 2019).