At long last, we’ve seen what could be the building of memories lighting up in the brains of mice.
Although scientists have long known the construction of memories to be a sequenced pattern of neurons replaying over and over again, the pattern in which these neurons fired was a murky unknown. The notoriously mysterious process of building memories had become somewhat like a legendary Lego set with a missing instruction manual – where you knew what the end structure looked like, but had no way of knowing how to build it.
To get a look at this hidden ‘instruction manual’ or the pattern of memory formation, Rosa Cossart and her team at The Institut de Neurobiologie de la Méditerranée, in Marseille, France, added a fluorescent protein to the neurons of four subject mice. The specific protein would fluoresce, or glow, when calcium ions flood into the neuron- a major sign that the neuron was actively firing. The team used this fluorescence to map neuron activity with a broad range, allowing for a much easier method of understanding exactly how the memories of mice were being formed.
Using the florescent proteins, the team analyzed the activity of over 1000 nuerons per mouse, as the mice walked on a treadmill or stood still. Since neurons are known to memorize the distances they have traveled, the treadmill provided a perfect “memory” that the mice would memorize and the scientists could watch.
As expected, when the mice were running, the neurons that traced the distance the mouse traveled fired in a simple sequential pattern, keeping track. But intriguingly, these same cells lit up later when the mice were resting – only in a swifter pattern. Instead of a single neuron lighting up and transmitting it’s light to the next one, the neurons were “memorizing” in entire chunks of neurons, separating and retracing their experience on the treadmill in segments. Furthermore, these neurons corresponding to each “segment” of memory weren’t located next to each other – but were instead scattered throughout the brain – suggesting that the memorization was not only carried out in segments, but also in a multifarious facet of different locations.
While Cossart and her team believe the activity of these grouped neurons are highly plausible as the “primary building blocks of memory”, Dr. Dragoi at Yale University is ambivalent. “It’s not clear if the mice actually formed the memories while they were running”, he quoted to New Scientist, “the groups of neurons that fired may have simply been default brain activity.” Kamran Diba of the University of Wisconsin agreed, quoting “The cells essentially fired in order throughout the run..So why would they break down into discrete assemblies later?”
However, despite the uncertain scrutiny of other scientists, it is undeniable that the study has great importance in the still nebulous world of neuroscience. And with just enough research, the hopeful path to finding that legendary Lego manual could now be a few steps closer.

Photo Credits: By UNI Düsseldorf (C. & O. Vogt-Institut) [CC BY 2.5 (], via Wikimedia Commons