July 29, 2025
The Main Idea
‘Mental time travel’ can restore memories to their former state, new study finds
By Krystal Kasal from Phys.org, edited by Lisa Lock, reviewed by Robert Egan
What We Know About Forgotten Memories
Several studies have shown that forgotten memories might not be as impossible to get back as we once thought. Memory seems to be closely connected to the situation in which it was made. This means that remembering smells, sounds, and other things from the environment, as well as any feelings you had when the memory was formed, can help you recall the memory. However, these memory studies haven’t really figured out how this kind of memory recall is forgotten after you remember it.
Most people know that remembering something usually gets harder and harder as time goes on. But the rate at which we forget actually slows down over time in an uneven way because our brains keep working on organizing memories. In other words, humans will forget an event faster within the first few days or weeks, and then the forgetting levels off somewhat and less of the memory is lost over longer time periods.
What the Scientists Wanted to Find Out
In a new study published in the Proceedings of the National Academy of Sciences, a group of German scientists wanted to find out if remembering memories with “mental time travel” can restore how well you can remember them and how fast you forget them to how they were shortly after you first learned them.
To do this, they recruited 1,216 people to do two different memory experiments.
How the Experiment Worked
The participants were split into four groups for each experiment. In the first experiment, the groups had to remember a list of words, and in the second experiment, participants were given a passage to read.
One group from each experiment was asked to recall the material without any form of mental time travel (called “context reinstatement”). The other groups used context reinstatement by remembering their thoughts and feelings during the time they first learned the material. These groups were asked to recall the materials at different times: either 4 hours, 24 hours, or 7 days after initially learning the materials.
What the Scientists Expected
The scientists expected to see a kind of rejuvenation (refreshing) of the memories. “The rejuvenation hypothesis assumes that mentally traveling back to the time when the older memories were originally learned reverses these effects: It makes the memories easier to remember right after the mental time travel as well as makes them fade away at the same rate as they did originally, effectively creating a copy of how the memories were at an earlier point in time.”
What They Found
And that is basically what the experiment showed. The researchers found that after context reinstatement, the participants’ forgetting pattern reversed course and closely matched the original forgetting curve right after the memory was first made. But this didn’t happen with the participants who did not use the mental time travel methods.
However, this method worked better when the time between learning the memory and doing the reinstatement was shorter – at 4 or 24 hours – compared to the longer time of 7 days. The chance of bringing back the memory through context reinstatement and how much of the memory came back got weaker at longer time intervals.
The Sisyphus Comparison
The study authors compare the idea of memory resurrection to the myth of Sisyphus rolling his boulder up a hill, only for it to fall back down again. They say, “The reversal made the memories similar again to how they were at an earlier point in time, with forgetting after mental time travel following the very same path as forgetting after first learning.”
“This picture of a Sisyphus-like resurrection of memories is different from the idea that context reinstatement caused by mental time travel is just a temporary thing. If it were temporary, the memory improvement should have disappeared shortly after trying the reinstatement, and how well you could remember things would quickly become the same as if you hadn’t tried reinstatement at all.”
What This Means for Real Life
The study offers some hope that old memories can be brought back, but there are some differences between memories made in real life and those used in this experiment. It’s possible that the richer, real-life situations in which memories are often made may create stronger rejuvenation effects, but more research is needed to find out how this effect might be different outside the lab and whether some memories might be rejuvenated after longer periods of time.
How Mental Time Travel Works
Mental time travel, or context reinstatement, works by having you remember:
- What you were thinking when you first learned something
- How you were feeling at that time
- What the environment was like (sounds, smells, sights)
- Any other details from when the memory was first formed
When you do this, your brain essentially “resets” the memory to act like it’s fresh again, making it easier to remember and causing it to fade at the same rate it did when it was new.
The Bottom Line
This research shows that there might be ways to make old memories work like new ones again, at least for a while. By using mental time travel techniques, you might be able to remember things better, especially if you try this method within the first day or two after learning something.
However, scientists still need to do more research to understand how well this works with real-life memories and whether it can help with memories that are much older than a week.
More information: The full study is called “Reinstating memories’ temporal context at encoding causes Sisyphus-like memory rejuvenation” and was published in the Proceedings of the National Academy of Sciences in 2025.
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