When you save a piece of data to a spinning disk drive, it is physically ‘written’ onto that disk in a specific place. While it can be moved, saved information will generally remain where it is unless there is a reason to rewrite it somewhere else.

Most people intuitively assume that our brains are the same. When you make a memory, it is ‘written’ somewhere in our brain so that it can be accessed and used again in the future. According to a a new study published by a team of neuroscientists at Northwestern University, however, that doesn’t seem to be the case.

The researchers looked into the hippocampus, which is the part of the brain primarily used for spatial memory. The study itself was based off a 2013 study from the journal Nature Neuroscience, which showed that neurons in the hippocampus are able to change patterns over time. To put it simply, that memories are physically moved around in the brain.

In this new study, the researchers placed mice on a treadmill where they controlled what they saw by using display screens all around it. They also played white noise to control for sound, and pumped in smells to attempt to minimize the impact that the olfactory sense would have on the experiment.

The screens displayed the inside of a maze, which remained the same for each session on the treadmill. During the experiment, the mouse was monitored using imaging devices that are able to track brain activity in real time, which was observed by the neuroscientists.

Going into the experiment, the researchers thought that the neuron’s would only shift if and when the mouses experience changed. For example, if the maze were adjusted. They assumed that by making sure that each experience the mouse had was as similar as possible, the ‘representation drift’ (what the movement of neurons has been called) would be minimal. The lead author of the study, Daniel Dombeck, told Live Science:

“I was sure we were going to reduce this representational drift. I was sure that the memory was going to look more stable over days — and that’s not what we found.”

The representation drift was instead significant, showing that the memories in the brain are being moved around, even when they are very similar to what they had already experienced. Additional study will undoubtedly be needed on this to try to figure out how often memories are shifted and why.

One theory could be that the more the mouse experiences something, the more important its brain will treat it, so the memory gets moved to a part of the brain for longer term storage, or possibly for accessing it more rapidly. Another could be that it is necessary to access and move the memory as often as possible to keep it active in the brain. Or it could be something else entirely.

The researchers do acknowledge some limitations in their study, especially when it comes to the smells in the experiment since they are extremely difficult to control for. Future studies will be needed to further confirm what these scientists found.

It would also be helpful to perform a similar study on humans (or at least other mammals) to see how similarly our brains work to the mice.

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