Research shows that your mind reinterprets events from the past with a nod to the present.
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 makes your memory quite unlike the video camera you may imagine it to be. But new research in the Journal of Neuroscience suggests it's very effective for helping us adapt to our environments, said co-author Joel Voss, a researcher at Northwestern University's Feinberg School of Medicine.
Voss' findings build on others and may also explain why we can be thoroughly convinced that something happened when it didn't, and why eyewitness testimony is notoriously unreliable.
The new research also suggests that memory problems like those seen in Alzheimer's could involve 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 17 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 new 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 that the part of the brain that retains memory is the same as the part that brings 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.
Addis said she also thinks the research has implications for understanding imagination and our social interactions.
"Being able to be cognitively flexible allows us to build an up-to-date understanding of the people around us and to navigate the social world," she said.