Why our brain "erases" memories from childhood: scientific explanation

No one in the world can remember the first few years of their life. At best, we remember some vivid fragments, and these cannot be events that happened before we turned 2-3 years old. In science, the inability to retain these memories is called childhood amnesia. But have you ever wondered why nature has put this mechanism in us and does not "record" what happens to us at the dawn of life?

Live Science asked neuroscientists what they already know about this topic. After all, we don't keep extremely emotional moments in our memory, such as our first steps and words, the time when our relationship with our parents is full of unconditional love, and so on.

Science shows that young children are actually able to memorize a lot of information. This is how they instantly learn who their parents are and how they learn to say "thank you" to a candy gift, even when they don't speak very well. Scientists call this semantic memory. However, at the age of about 2-4 years, children lack another type of memory - episodic memory. It is responsible for memorizing details of specific events. Such memories are stored in several parts of the brain's surface - its cortex. Thus, sounds are processed by the auditory cortex on the sides of the brain, and visual memory is controlled by the visual cortex at the back. An area of the brain called the hippocampus ties all the disparate parts together.

But the brain of a young child is not yet able to combine information into complex neural structures, which is essentially what memories are. So, memorization does occur at this age, but it does not form a complete picture.

"If you think of your cerebral cortex as a flower bed, then the entire top of your head is covered with flowers," Patricia Bauer, a professor of psychology at Emory University, explained to the publication. "The hippocampus, which is very neatly located in the middle of your brain, is responsible for putting them all together and tying them into a bouquet." A memory is a bouquet, a neural pattern of connections between parts of the brain where memories are stored," she added.

And it is the immaturity of the hippocampus that is responsible for the lack of early memories. It is only at the age of 2-4 that it begins to link fragments of information together. As Nora Newcomb, a professor of psychology at Temple University in Philadelphia, explained, episodic memory can be incredibly complex in children under this age. The child is exploring the world and absorbing a huge amount of information. "I think the main goal of the first two years of learning is to acquire semantic knowledge, and from that perspective, episodic memory can be really distracting," Newcomb said. "That is, in the first years of life, we collect a certain 'collection' of disparate facts from which we create a picture of the world later.

However, there is another theory. According to it, we still retain the earliest memories of childhood, but it is difficult for us to retrieve them from memory as adults. This may be evidenced by the results of a study published in 2023 in the journal Science Advances. The study showed that "lost" childhood memories can be restored in adult mice by stimulating the neural pathways associated with specific memories with light.

The authors of the study aimed to examine developmental factors that can affect childhood amnesia. They found that mice with autism spectrum disorders (ASD) were able to recall some things from their early childhood.

Autism has many causes, but it was previously linked to the overactivation of the mother's immune system during pregnancy. Therefore, in order to develop mice with ASD, researchers stimulated the immune system of females during pregnancy. It turned out that this activation helped prevent the loss of early memories in their cubs. It affected the size and plasticity of specialized memory cells in their brains. When these cells were optically stimulated in adult mice without signs of autism, forgotten memories could be recovered.

"These new findings show that immune activation during pregnancy leads to a change in brain state that alters our innate but reversible 'forgetting switches' that determine whether childhood memories are forgotten," said co-author Thomas Ryan, an associate professor of biochemistry at Trinity College Dublin in Ireland, in a statement about the study.

At the moment, the scientists point out that they studied only mice and cannot say for sure whether the same mechanisms work in humans. However, they argue that their work is important for improving our understanding of memory and forgetting during child development. In addition, they shed some light on understanding general cognitive flexibility in the context of autism.

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