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Scientists Find Evidence That Memories in Brain Are Physically Moving Around

Anyone who makes a habit of losing their keys has a new excuse: you didn’t forget — your memory just moved.

That’s courtesy of neuroscientists at Northwestern University, who recently published a study looking into the brain patterns of mice.

The new research explores how the hippocampus — a crucial part of the brain for spatial memory — changes over time. The paper sheds new light on a phenomenon first uncovered in 2013, when a study in the journal Nature Neuroscience found that neurons in the hippocampus can change their patterns over time — that memories related to place, in a meta twist, are literally moving around in the brain.

To conduct the experiment, mice were set on a treadmill flanked by screens on all sides. The screens showed the innards of a maze, which the mice were able to explore based on how they navigated the treadmill. A familiar scent was likewise pumped in, while white noise was played in the background.

Though the mice were subjected to a number of cardio sessions over several days, the layout of the maze, the scent, and the noise for the control group remained the same throughout.

Using high-tech imaging devices to track brain activity in real-time, the Northwestern researchers observed changes in the mouse’s brains as they navigated the virtual environment.

Interestingly, the researchers found that this recently-uncovered neuron-shifting phenomenon, termed “representation drift,” occurred regardless of changes to the mouse’s environment.

The results would seem to dispel the idea that representation drift has mostly to do with a mouse’s surroundings — the exact opposite hypothesis the researchers went in with.

“I was sure we were going to reduce this representational drift,” Daniel Dombeck, the lead author of the study told Live Science. “I was sure that the memory was going to look more stable over days — and that’s not what we found.”

Instead, the study authors hypothesize, representation drift could just be the brain’s way of sorting new but familiar information as it collects it — like a return visit to your favorite restaurant.

Still, there are some limitations, and as is usually the case, and further research is needed to expand on this fascinating finding. For one thing, these are mice, and though both mice and humans are mammals, human brains are vastly larger and more sophisticated in ways both large and small. (That said, the study’s authors note that representational drift has been recorded across many parts of the brains of many species, including humans.)

Another notoriously difficult factor to control for is scent, as the study notes that “mouse behavior can be strongly affected by even small changes in the sensory environment.”

Going into it, the team reasoned that “the olfactory environment —particularly surface odors, which are difficult to clean, could change over days and be detected by the mice — was a significant uncontrolled sensory feature in previous mouse… representational drift studies.”

Nonetheless, the team found that their observed drift rate was comparable regardless of whether odor was controlled, and even when it was purposefully made to fluctuate over several days. In essence, they write, “only sensory modalities with behavioral relevance have a strong influence on the cognitive map.”

It’s currently unclear how this kind of internal neuron moving affects our understanding of memory — but it’s certainly a study to remember.

More on neuroscience: The Microplastics in Your Brain May Be Causing Mental Health Issues



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