A new study reveals that our memories of familiar places are not stored fixed in our brain, contrary to what scientists have thought for 50 years. The neurons that code this spatial information constantly “derives”, transporting our mental cards from one neural network to another. This major discovery upsets our understanding of memory and opens up unprecedented perspectives to fight against its age -related decline.
The fall of a scientific dogma
For decades, the scientific community was convinced of having pierced the mystery of our mental navigation. In the hippocampus, a crucial region for memory, specialized “place cells” were supposed to create a stable mental map of our environment. Each familiar place owned its dedicated neurons, trusted faithfully to each visit as unchanging headlights in the ocean of our conscience.
This reassuring vision struck in 2013 when a revolutionary study observed that these alleged mental cards constantly fluctuated. The neuroscientists then discovered a disturbing phenomenon: the “hippocampal representational drift”, where our memories of places literally migrate from one group of neurons to another.
The experience that changes everything
Daniel Dombeck and his Northwestern University team wanted to definitively decide this controversy. Their approach? Create the most controlled environment as possible thanks to virtual reality. Mouses have been placed on treadmills in front of screens, sailing in a virtual labyrinth identical to each session.
The researchers pushed control to the extreme: same odor diffused in a cone placed on the muzzle of each animal, constant white noise, identical movement speed. Meanwhile, a window open in the skull of mice made it possible to observe in real time the activity of their neurons thanks to fluorescent markers.
Dombeck was convinced that this perfect control would finally stabilize the mental cards. He was wrong.
Nomadic memory
The results, published in Nature
Neuroscience, confirmed the unthinkable: our space memories are in perpetual movement. Only 5 to 10% of observed neurons behaved like traditional place cells, constantly activating for specific places. These rare stable cells shared a common characteristic: high excitability, making them more reactive to stimuli.
Conversely, less excitable neurons showed a constant drift, changing their spatial “specialization” over the days. This discovery reveals that our brain does not store places as frozen GPS coordinates, but rather as fluid memories, constantly rewritten.
Why does our brain sabotage our mental cards?
This apparent instability actually hides remarkable intelligence. Dombeck proposes that this drift is used to distinguish our different visits from the same place. Thanks to this neuronal “update”, your brain can separate your lunch from yesterday to today’s restaurant, creating distinct episodic memories rather than a confused mass of similar experiences.
The drift would thus work as a biological clock, allowing the brain to mark the passage of time and organize our experiences in distinct chapters of our personal history.
Credit: ISTOCK
Credits: Metamorworks/Istock
Vertiginous implications
This research illuminates the mysteries of brain aging by a new day. With age, our neurons lose their excitability, which could explain why our memories become less precise and more confused. If the few stable cells that anchor our memories lose their responsiveness, our whole mental navigation system is crumbling.
This understanding opens fascinating therapeutic perspectives. Dombeck speculates that by now or in restaurants neuronal excitability, we could preserve our memory capacities in the face of the passing time.
A more complex brain than expected
Although conducted on mice, this study probably reveals a universal mechanism in mammals. It reminds us that our brain, far from being a organic hard drive storing fixed data, rather resembles a dynamic system in perpetual reorganization.
Every day, without us being aware of it, our brain rewrites the history of our familiar places. This instability, far from being a defect, could well be one of the keys to our extraordinary ability to navigate in a constantly evolving world while keeping traces of our past.