Memory is an essential part of our existence. Who we are, what we know and what we think can all be derived from our ability to remember. How reliable, though, are our memories?
A study, published in the Journal of Neuroscience today, suggests that the answer is “not nearly as much as we once thought”.
The researchers, based at Chicago’s Northwestern University Feinberg School of Medicine, conducted a test in which they showed participants an image of an object placed in front of a background. They were then shown a different background and asked to move the object to the same location as before.
In each case in the second exercise, the participants failed to place tho object correctly. They were then asked to return to the first background and place the object in its original spot. When faced with the choice, all selected the second, incorrect location. The participants’ memories had, essentially, been “edited”.
It is now increasingly being established that our memories are susceptible to modification. Indeed, recent research has shown that we rewrite memories each time we recall them. In some cases, recollections can even be entirely fabricated.
Jee Hyun Kim from the Florey Institute of Neuroscience and Mental Health in Melbourne said this study adds a new dimension to our understanding of memory.
“We knew from animal studies that memories update and incorporate new information, to the extent of having false memories,” she said.
“However, the memories formed were based on emotionally significant events.”
The experiment, Dr Kim noted, proved that memory adaptation was not limited to traumatic events.
“Even benign episodes can ‘update’ to incorporate new information,” she said.
Kristyn Bates, from the University of Western Australia, agreed on the significance of the study.
“Traditionally, we have learned much about brain function from people who suffer brain injuries and disease by relating their symptoms and deficits to the [affected] sites in the brain,” she said.
“But now with brain imaging techniques, we can study these processes in living, healthy volunteers.”
To better understand the neurological side to this process, the researchers directed participants to complete the test within an MRI scanner.
They found the memory-rewriting process was a result of activity in the hippocampus, a part of the brain affected in dementia cases.
The tests also helped show how memory was capable of being manipulated. Dr Kim said children “are highly susceptible to external suggestions”, as are hypnosis patients.
So why are our memories so susceptible to change? The authors of the study suggest this process is a means of enabling our brains to adapt to changing environments. By inserting new data into old recollections, our memories retain relevance to our current situation.
Some types of memories may be more flexible than others. Semantic memories — the recollections that comprise our conceptual understandings — are relatively stable, but episodic and experiential memories can be much more unreliable.
Fiona Kumfor, research officer at Neuroscience Research Australia, said we should not automatically dismiss memories as untrustworthy. The results of the study “highlight some of the shortcomings of our memories”, she said, but they “shouldn’t make us doubt the truth” of what we recall.
In some cases the recollection process can have the opposite effect.
“Each time you reminisce about a past event, that memory will strengthen and be reinforced,” she said.