Try to think back to your second birthday. Almost no one actually succeeds. What we think we remember, in most cases, is a construction made up of stories heard a thousand times and images seen in family albums. Childhood amnesia, that is, the inability to remember the first years of life, is a condition common to almost all human beings. And today science is starting to explain why.
For a long time it was thought that forgetting the early years was a sort of technical limit of the immature brain. A temporary problem, destined to be resolved with growth. The new research tells a different and, in a certain sense, more fascinating story: the brain doesn’t lose those memories out of inability, it puts them aside on purpose.
In the first few years of life we learn a lot. Language, relationships, social rules, emotions. It is a phase of intense and continuous learning. Precisely for this reason, neuroscientists explain, the brain needs to make space, reorganize, simplify. And to do this, a little-known but fundamental mechanism comes into play.
Microglia, the “scavenger” cells of the brain that decide what to remember
Special cells called microglia live in our brain. They are part of the immune system and have the task of maintaining the balance of the brain environment. During childhood, when the brain is in full construction, these cells work tirelessly to refine the connections between neurons, eliminating the least useful ones and strengthening the others.
A group of researchers from Trinity College Dublin observed that this very “reordering” activity seems to be linked to the disappearance of the oldest memories. Under experimental conditions, when the action of microglia is temporarily attenuated, memory traces remain more accessible. Not because they get stronger, but because they aren’t stored as deeply.
The key point is this: childhood memories are not erased as useless files, but silenced, put into the background to allow the brain to adapt to a rapidly changing world.
Memories don’t really disappear
Thanks to increasingly refined observation techniques, researchers have been able to identify so-called “memory traces”, groups of neurons that preserve a lived experience. Even when a memory can no longer be consciously recalled, those traces continue to exist.
The areas involved are the same ones we use every day to remember places, emotions and situations: the hippocampus and the amygdala. The difference is that, as time passes, access to those tracks is regulated, as if the brain decides to no longer make them central to our adult lives.
According to Erika Stewart, now a researcher at Columbia University, microglia behave like real “memory managers”, helping the brain decide which memories to keep active and which to leave in the background.
An interesting aspect of this research concerns the link between the immune system and brain development. Under some conditions, this balance can change, also influencing the way memory is organized in the first years of life.
Scientists underline that for harmonious development a sort of “middle ground” is needed: an activity of the microglia that is neither excessive nor too reduced. It is a delicate balance, which could also help us better understand individual differences in the way we remember, learn and perceive the world.
Forgetting to grow
Childhood amnesia is probably the most widespread form of forgetfulness that exists. And precisely because it unites us all, we rarely stop to ask ourselves what sense it makes. Today we know that forgetting is an integral part of learning, a way to make the brain more flexible, ready to face new experiences without being overloaded by the past.
As Tomás Ryan, senior author of the study published in PLOS Biology, explains, memory is not a static archive, but a dynamic system, which changes with us throughout our lives.
And perhaps this is precisely the most reassuring thought: if we don’t remember our first steps or first words, it’s not because something went wrong. It’s because our brains were silently making room for what we would become.
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