A new study shows that microglial cells function as memory managers, obsessively erasing our earliest memories to make room for new ones. It’s not a defect, it’s a characteristic: they function as “file organizers” in our brain.
Try to remember your first birthday party. You’ll probably be able to conjure up a vague image based on a photo your parents have shown you thousands of times. This mental image is very probably false.
The truth is that most people barely remember anything before 3 years of age. It’s a phenomenon called childhood amnesiaand is considered one of the great paradoxes of the human being.
We spend our first few years absorbing information like sponges, but our brains seem determined to Press the “delete” button on almost everything.
For a long time, neuroscientists treated this forgetting as a cognitive failure or a simple lack of brain maturity. But a new study suggests that childhood amnesia is actually a feature and not a defect — and is being managed by an unexpected team of “cellular caregivers”.
The results of the study, published Tuesday in the journal PLOS Biologyshow that the microglial cellsimmune cells from the neuralgic tissue of the central nervous system, may be actively erasing our first memories.
Memory managers
We typically think of the immune system as our body’s defense force, hunting pathogens and eliminating waste. But in the brain, the immune cells have an everyday function which is much more similar to the computer systems management.
Microglial cells are specialized macrophages which represent about 10 to 15% of the cells found in the brain. During rapid early childhood development, are busy pruning synapses — the connections between neurons — to refine brain circuits, explains .
In the new study, a team of researchers from Trinity College Dublin wanted to know whether this “pruning” process was responsible for the loss of first memories. They worked with baby mice that, like humans, forget their scary experiences they learned as babies.
The team, led by Erika Stewart e Thomas Ryantrained 17-day-old mice to associate a specific box with a slight shock legs.
Under normal conditions, these mice would forget this experience scary when they reach the 25 days old. Essentially, they would leave the memory behind as they grow up.
But when researchers gave mice minocyclinean antibiotic that inhibits the activity of microglia, something remarkable happened. The mice have not lost their memories.
Even eight days later, a lifetime in a mouse’s childhood, the mice treated they were paralyzed with fear when placed back in the box. By telling the immune system to take a break, researchers had effectively stopped childhood amnesia.
Luminous traces of the past
To prove that the memories were still physically there, the team used a technique called genetic “marking” to make the specific neurons that hold the memory — known as “engramas” — glow with a fluorescent protein (EYFP).
The technique allowed them literally see the memory trail in the brain. In mice with active microglia (those that forgot), memory engrams were less active during recall. But in mice treated with the inhibitor, the memory engrams in the amygdala lit up with activity.
The memory files had not been corrupted; they had just been protected crusher.
When the researchers looked more closely at the cellular level, they saw that inhibiting microglia changed the way these immune cells interacted with memory neurons. In treated mice, there were fewer points of contact between microglia and engram cells. Essentially, by keeping the “memory managers” at bay, the memory was preserved.
“Microglia, the resident immune cells of the central nervous system, can be considered the ‘memory managers in the brain“, explains Erika Stewart in a statement published on .
“Our paper highlights its role specifically in childhood amnesia and indicates that there may be common mechanisms between childhood amnesia and other forms of forgetfulness — both in everyday life and in illness”, adds the first author of the study.
A feature, not a defect
Why would evolution design a brain that erases its own data? Tomás Rya, suggests that forgetting is a crucial part the way we learn.
“Childhood amnesia is possibly the most ubiquitous form of memory loss in the human population,” notes Ryan. “Most of us don’t remember anything from the first few years of our lives, despite having so many new experiences during these formative years.. This is a neglected topic in memory research, precisely because we all accept it as a fact of life.”
“But What if those memories are still present in the brain? Increasingly, the field of memory views forgetting as a ‘feature’ of the brain rather than a ‘defect,’” adds the study’s lead author.
“It seems that the brain is archiving neural units which store memory, engrams, for later use. Microglia appear to be functioning in the brain to help organize the way engrams are stored and expressed throughout life,” concludes Ryan.
The implications here are huge. If we can chemically switch the ability to access early memories in mice, we are one step closer to understanding how memory persistence works in humans.
For now, if you can’t remember your second birthday, don’t worry. It just means that your microglia were doing their jobdiligently sculpting your brain to be ready for the world.
