The mystery of infantile amnesia

Those who remember their first years of life are extremely rare. Armed with latest -crying medical imaging devices, researchers are trying to know why. Their discoveries on infantile amnesia are surprising.

Babies

A team of researchers from Yale University, in Connecticut, have measured what is happening in the brain of 3 -year -old toddlers when one of their own memories, and when we present a memory belonging to another child.

“Everyone experiences infantile amnesia, the fact that we do not remember our first years of life,” notes the neurobiologist Nick Turk-Browne. But the idea that these memories have never been recorded in our brain, that babies have no long -term memory, is wrong. We have shown that when babies are reminded of memories, their hippocampus is stimulated, but not when we show them the memories of another baby. The hippocampus is a region of the brain involved in memory.

How long do babies from 18 to 24 months old keep memories? And does this capacity vary according to individuals? This is what an Irish neuropsychologist at the Max-Planck Institute for Human Development is trying to measure in Berlin.

Sarah Power’s data could help see whether individual variations in infantile amnesia are linked to future characteristics, for example academic success or disorders such as hyperactivity with or without attention deficit.

“We have built an immersive environment for our 360 small subjects,” explains M^me Power. For example, when a jungle is projected on the walls of the room, the object they must find is in the box A. But when an underwater environment is on the walls of the room, the object is in the B box. We look at if they remember after one, three and six months. »»

The mice

Another generalized idea is wrong, demonstrated Sarah Power, following his research on the mice during his doctorate at the Trinity College in Dublin. “We often consider that infantile amnesia means that memories of the first years are erased from the brain at a certain point,” she notes. At the mouse, we have shown that they are there, but that we do not have access to it. However, it is possible to reactivate these memories. »»

The instigator of this work at Trinity College, Thomas Ryan, had shown in 2014, during his doctorate at the Massachusetts Institute of Technology (MIT), that it was possible to create and block memories in mice, thanks to an invasive technology called “optogenetics”. The biological traces of these memories in the brain are called “engrams”.

“Sarah has shown that you can block a specific engram and then restore access to this memory to the mouse,” said Mr. Ryan. But we do not know if it is a general memory, for example knowing how to press a lever, or the memory of a particular event. The mice do not tell us. It is for this reason that we must continue studies on babies. Obviously, we cannot use optogenetics, it’s too invasive. »»

The next step in animal studies on infantile amnesia is to determine whether “microglial” cells, which protect the brain from infections, play a role in infantile amnesia, as several studies suggest.

“There could be an influence of the immune system, in any case microglial cells, on memory,” says Mr. Ryan. There is also work showing that autism, which can be considered as a difficulty in learning social codes and controlling certain obsessions, could be caused by inflammation during pregnancy, which would cause an immune response. »»

Hypotheses

Human has too big head, observes Thomas Ryan. Babies are therefore born before their brain is completely developed, because they could not stay in their mother’s belly any longer. But most mammals, giraffes for example, can behave like adults a few days after birth, because they have almost finished their development when they come to the world.

The years of human infantile amnesia correspond to this additional development period that mammals pass through their mother’s belly, while babies must finish their development after getting out of it.

The first learnings require a virgin soil. “There is always a tension between memories and the ability to learn new things,” said Mr. Turk-Browne. If we trust too much about our past experiences, we learn less. Infantile amnesia perhaps reflects the need to acquire the most new knowledge in the first years of life ”, which leaves less room to store memories.

The baby does not understand what he sees. “Imagine a 1-year-old baby who visits his grandfather with his parents. He does not understand the conversation, he may not recognize that he is in a kitchen because there is a fridge and a stove. But the 3 -year -old child has developed more experience in language and social environments. »»

When a 1 year old baby “encodes” his memories, he does not do so in the same way as a 3 -year -old child who begins to master language. So at 3 years old, a child may no longer understand the memories stored before. “He becomes unable to understand how he thought when he was a baby,” observes Nick Turk-Browne. Once you master language, “when you create a memory, you create it with words”.

The baby does not understand his emotions either. “Emotions are inseparable from memories,” says Ciara Greene, specialist in memory disorders at the Dublin university college. “We are born with the ability to feel emotions, but not necessarily that of defining them. There may be a misunderstanding of the emotions felt when you were a baby, who were badly cataloged by memory.