Context plays a big role in our memories, both good and bad. For example, there's probably a song that reminds you of your first love - a song you used to like, but now seriously can't stand.
Sometimes these memories can be pleasant. But equally they can be particularly painful and something you want to forget.
Thanks to new research, people may soon be able to forget past experiences by changing how they think about the context of those memories.
Scientists believe the finding could help provide better treatments for people with post-traumatic stress disorder (PTSD).
For some time, memory theorists have known that we use context - such as sights, sounds and smells - to organise and retrieve memories.
But researchers wanted to know whether and how people can intentionally forget past experiences.
They designed a functional magnetic resonance imaging (fMRI) experiment to specifically track thoughts related to memory contexts.
Usually in memory studies, subjects are asked to memorise and recall a list of unrelated words.
In this particular study, however, researchers showed participants images of outdoor scenes - such as forests, mountains and beaches - as they studied two lists of random words, manipulating whether they were told to forget or remember the first list prior to studying the second list.
"Our hope was the scene images would bias the background, or contextual, thoughts that people had as they studied the words to include scene-related thoughts," explained lead author Jeremy Manning, an assistant professor of psychological and brain sciences at Dartmouth.
"We used fMRI to track how much people were thinking of scene-related things at each moment during our experiment.
"That allowed us to track, on a moment-by-moment basis, how those scene or context representations faded in and out of people's thoughts over time."
Participants were told to either forget or remember the random words presented to them interspersed between scene images.
Right after they were told to forget, the fMRI showed that they "flushed out" the scene-related activity from their brains.
"It's like intentionally pushing thoughts of your grandmother's cooking out of your mind if you don't want to think about your grandmother at that moment," Manning said.
"We were able to physically measure and quantify that process using brain data."
When the researchers told participants to remember the studied list rather than forget it, this flushing out of scene-related thoughts didn't occur.
Additionally, the amount that people flushed out scene-related thoughts predicted how many of the studied words they would later remember, which shows the process is effective at facilitating forgetting.
Researchers said the study's findings could aid people with PTSD - for example soldiers who wanted to forget traumatic events - by helping them to intentionally forget.
"Or we might want to get old information 'out of our head', so we can focus on learning new material,"explained Manning. "Our study identified one mechanism that supports these processes."
The study was published in the journal Psychonomic Bulletin and Review.
