A good raconteur is able to bring to life the vivid details of a story, painting an intricate picture in the minds of the listeners. The problem is that although humans are quite good at remembering the broad nature of events, they are bad when it comes to the specifics. Worse still, we are often not even aware of this. Studies have shown a propensity to make up details we can’t remember unconsciously, a habit which causes problems in courts.
A new study, published in eLife, helps explain why this is the case. Researchers from the University of Toronto observed how rats’ brains coded information when given two memories which shared a common stimulus relationship, and how these codes changed over time. Their study found that neurons in the medial prefrontal cortex (mPFC) of the brain were responsible for the loss of detail.
"This experiment revealed that groups of neurons in the mPFC initially encode both the unique and shared features of the stimuli in a similar way," explained first author Mark Morrissey. "However, over the course of a month, the coding becomes more sensitive to the shared features and less sensitive to the unique features, which become lost."
This may force people to ad-lib from time to time when retelling old stories, but in other ways generalising memories is useful. Further research finds that our brains are able immediately to apply these generalised memories to entirely new situations. Whereas the unique details of a memory may not prove useful later on, details which are shared across multiple memories are more likely to be applicable in the future.
Small details may give stories their depth, but it is the lessons to be learnt that give them their meaning.