What scientists know about infantile amnesia

Whenever I teach about memory in my child development class at Rutgers University, I begin by asking my students to recall their earliest memories. Some students talk about their first day of Pre-K; others talk about a time when they were hurt or upset; some cite the day their younger sibling was born.

Despite the large differences in detail, these memories do have a few things in common: they are all autobiographical, or memories of significant experiences in the person’s life, and usually did not occur before age 2 or 3. Most people can’t remember events from the first few years of their lives, a phenomenon researchers have called infantile amnesia. But why can’t we remember the things that happened to us when we were babies? Does memory begin to work only at a certain age?

Here’s what researchers know about babies and memory.

While people can’t remember much before age 2 or 3, research shows that babies can form memories — just not the memories you tell about yourself. In the first few days of life, babies can remember their own mother’s face and distinguish it from the face of a stranger. A few months later, babies can demonstrate that they remember very familiar faces by smiling the most at those they see most often.

How learning happens in the brains of sleeping babies

There are many different types of memories besides those that are autobiographical. There are semantic or factual memories, such as the names of different varieties of apples or the capital of your home state. There are also procedural memories, or memories of how to perform an action – think of opening the front door or driving a car.

Research from psychologist Carolyn Rowe-Collier’s lab in the 1980s and 1990s showed that babies can form some of these other types of memories from an early age. Of course, babies can’t tell you exactly what they remember. So the key to Rovee-Collier’s research was designing a task that was sensitive to babies’ rapidly changing bodies and abilities to evaluate their memories over a long period of time.

In the version for 2- to 6-month-old babies, researchers place a baby in a crib with a cell phone hanging from the top. They measure how much the baby kicks to get an idea of ​​his natural tendency to move his legs. They then tie a string from the baby’s leg to the end of the mobile so that when the baby kicks, the mobile moves. As you can imagine, babies quickly learn that they are in control – they like to see the mobile device move and so they kick more than before the string was attached to their leg, showing that they have learned that kicking causes the mobile device to moves.

Sleep training can benefit some babies—and their parents

The version for children 6 to 18 months is similar. But instead of lying in a crib — which this age group refuses to do for very long — the baby sits on its parents’ lap with its hands on a lever that will eventually make the train move around the track. At first, the lever does not work, and the experimenters measure how much the baby naturally presses. Then they turn on the lever and every time the baby pushes it, the train moves along its track. Babies learn the game again quickly and push the lever significantly more when it makes the train move.

What does this have to do with memory? The cleverest part of this study is that after teaching the babies one of these tasks for several days, Rovee-Collier later tested whether they remembered it. When the pups returned to the lab, the researchers showed them the cell phone or train and measured whether they still kicked or pressed the lever.

Using this method, Rovee-Collier and colleagues found that at 6 months, if babies were trained for one minute, they could recall an event a day later. The older the babies were, the longer they remembered. She also found that teaching babies for longer periods of time and reminding them — for example, showing them the cell phone moves very briefly on its own — helps them remember events longer.

Why not autobiographical memoirs?

If babies can form memories in the first few months, why don’t people remember things from this earliest stage of their lives? It is not yet clear whether people experience infantile amnesia because we cannot form autobiographical memories, or we simply have no way to recover them. No one knows for sure what’s going on, but scientists have a few guesses.

Is my memory deteriorating or is it just normal aging?

One is that autobiographical memories require you to have some self-confidence. You must be able to think about your behavior in terms of how it relates to others. Researchers have tested this ability in the past using a mirror recognition task called the blush test. This involves marking the baby’s nose with a smear of red lipstick or rouge – or “rouge” as it was called in the 1970s when the task was created.

The researchers then placed the baby in front of a mirror. Babies under 18 months simply smile at the cute baby in the reflection, showing no sign of recognizing themselves or the red mark on their face. Between 18 and 24 months, toddlers touch their noses, even look embarrassed, suggesting that they associate the red dot in the mirror with their own face—they have some sense of self.

Another possible explanation for infantile amnesia is that because babies don’t have language until later in their second year of life, they can’t form narratives about their own lives that they can later recall.

Finally, the hippocampus, which is the area of ​​the brain largely responsible for memory, is not fully developed in infancy.

Scientists will continue to study how each of these factors may contribute to why you can’t remember much, if anything, about your life before age 2.

This article was originally published on theconversation.com.

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