Every time you pull up a memory – say of your first kiss – your mind reinterprets it for the present day, new research suggests. If you’re in the middle of an ugly divorce, for example, you might recall it differently than if you’re happily married and life is going well.
This fluke of memory, reported in a paper published in The Journal of Neuroscience, makes us lousy eyewitnesses to a crime. But it’s very effective for helping us adapt to our environment, said co-author Joel Voss, a researcher at Northwestern University’s Feinberg School of Medicine.
For our hunter-gatherer ancestors, for instance, it was more important to recall the location of the current year’s hunting grounds than to remember with exact detail where the best spot was a decade ago.
The new research also suggests memory problems such as those seen in Alzheimer’s are caused by a “freezing” of these memories – an inability to adapt the memory to the present, Voss said.
Our memories are thus less a snapshot of the past, than “a record of our current view on the past,” said Donna Rose Addis, a researcher and associate professor at the University of Auckland in New Zealand, who was not involved in the research.
Using brain scans of 20 healthy volunteers as they were taught new data and recalled previously learned information, Voss and his colleagues were able to show for the first time precisely when and where incorrect information gets implanted into existing memories.
When you build a new memory, you gather little bits of information – what the room looks like, who’s talking, what they’re wearing – and store them together. When you bring up an old memory, the bits of information get melded with new bits relevant to your present life, Voss said.
“A memory isn’t a static thing that you bring in and it slowly gets moved out and stuck somewhere in the brain,” he said. “Every time you retrieve it, you have the ability to modify it.”
He and his team are studying the role the part of the brain called the hippocampus plays in this modification process.
We tend to imagine that once we commit a fact to memory, it is shuttled into a warehouse somewhere in the brain and brought out only when needed, said Sam Gandy, a professor of neurology and psychiatry at the Icahn School of Medicine at Mt. Sinai in New York City. This study suggests instead the part of the brain retaining memory is the same as the part bringing it back up.
In post-traumatic stress disorder and depression, where this normal process gets disrupted, our memories may get stuck in one place or we become unable to imagine a different future, Addis said. She said she also thinks the research has implications for understanding imagination and our social interactions.
“Being able to be really flexible allows us to get a better understanding of the people around us and to navigate the social world,” she said.
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