The mechanism that allows certain memories to stick in the memory for a long time does not depend on a single switch, but on multiple “timers” in the brain.
Some memories fade away like meteors, others stay with us for a few weeks, and others for a lifetime. How does the brain decide which ones to fix or let go of? How do the tracks deemed “worthy” become indelibly imprinted in the memory? It is one of the key questions in neuroscience and the answer is still far away. However, a study published in Nature proposes an advanced and convincing model of this process.
Progressive skimming
According to the conclusions of scientists at Rockefeller University in New York, the process that allows a memory to remain fixed for a long time in the brain is gradual, involves different brain regions and is managed by multiple molecular signals that act as timers, to regulate the duration of that trace in the memory.
In short, it would not be a single on-off switch, as proposed in the past, that would transform a memory from a momentary flash into personal baggage; but a series of subsequent steps in which, several times, the relevance of that memory is evaluated. In these passages, as if due to progressive barriers, the less significant memories are labeled as to be abandoned, while the important ones progress towards forms of long-term memory.
Memory manipulators
The authors of the study created an experimental model in virtual reality in which, by varying the frequency in which certain experiences were proposed and repeated to the mice, they managed to decide which memories should be fixed in their brains more permanently than others.
At this point, using a platform based on the CRISPR gene editing technique, they managed to demonstrate that, by manipulating certain molecules that control the expression of genes in the thalamus and cortex, two regions crucial for memory, an impact on the duration of individual memories was obtained. Each molecule studied was able to influence the duration of a memory at a different moment, and for a different time.
What scientists have discovered is a “cascade of molecular signals” that unfold over time and in different brain regions: we can imagine them as many different timers, set to different durations, which “forward” some memories and leave others behind. Those that activate immediately deactivate just as quickly, while those that activate later remain active for a longer duration of time.
These timers are, in more scientific terms, transcriptional regulators, that is, proteins that control gene expression at the level of RNA transcription. Scientists studied three in particular: Camta1 ensures that, after a memory is formed in the hippocampus, it initially remains fixed in memory.
As time goes by, another switch, Tc4activates and provides structural support to prolong the stay of that trace in the brain. Even further, the protein Ash1l it can make that memory even more persistent.
If one of these steps does not happen, that memory is destined to be lost. As we can see, becoming fixed in long-term memory is a matter of subsequent evaluations and continuous adjustments. The discovery could contribute to research into diseases that involve memory loss, although much remains to be clarified: for example, what tells the brain which memories are worth carrying forward and which to forget?
